Final Submitted Dissertation

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Faculty of Health and Social Care
School of Health Sciences
Applied Sport and Exercise Science
Research Project
A COMPARISON OF UNILATERAL AND BILATERAL
LOWER BODY RESISTANCE AND PLYOMETRIC
TRAINING EFFECT ON SOCCER RELEVANT FITNESS
By David J Kidd
Supervisor: Dr Katherine Burgess
Word Count - 8492

MatriculationNumber:1203784
i
BSc (Hons) Applied Sport and Exercise Science
Assessment Submission
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1. All material in this assessment is my own work and that which is not my
own work has been identified. DK
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been changed to protect confidentiality of information. DK
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have completed an extenuating circumstances form and submitted it
along with the accompanying evidence to my course leader.
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Module number: HS4101
Module title: Research Project
Module leader: Dr Paul Swinton
Date of hand-in: 03 May 2016
Student number: 1203784
Word count: Main Content - 8492; References - 4509; Appendices - 4805; All
Other Content - 1542
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Table of Contents Page
Number
Declaration of Intellectual Ownership I
Table of Contents II
Tables and Figures IV
Table of Abbreviations V
Acknowledgements VI
Abstract VII
1 - Introduction 1
1.1 - Background 1
1.2 - Review of Literature 1
1.2.1 - Resistance Training 2
1.2.2 - Plyometric Training 4
1.2.3 - Combined Resistance and Plyometric Training 7
1.2.4 - Unilateral versus Bilateral Training 8
1.3 - Research Aims and Hypothesis 10
2 - Methodology 12
2.1 - Experimental Design 12
2.2 - Participants 12
2.3 - Testing Procedures 13
2.4 - Intervention 15
2.5 - Data Analysis 15
3 - Results 18
3.1 - Performance Variables 18
3.1.1 - Vertical Jump Height and Rate of Force Development 18
3.1.2 - Sprint Speed and Change of Direction 21
3.1.3 - Maximal Strength 23
3.2 - Comparison of Unilateral and Bilateral Training Effect 24
3.2.1 - Vertical Jump Height, Rate of Force Development and
Maximal Strength
24
3.2.2 - Sprint Speed 25
3.2.3 - Change of Direction Ability 26
4 - Discussion 27
4.1 - Jump Parameters 27
4.2 - Maximal Strength 29

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4.3 - Sprint Performance 29
4.4 - Change of Direction Ability 31
5 - Conclusion 34
6 - References 36
7 - Appendices 55

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Tables and Figures
Table/Figure Description Page
Number
Table 3.1 Baseline and Post Intervention Vertical Jump
Heights.
19
Table 3.2 Intervention Effect Sizes of both Experimental
Groups for VJH and MS data
24
Figure 1.1 Relative Improvement in Maximal Leg Strength
following RT intervention in soccer players.
3
Figure 1.2 Forest Graph of PT intervention effectiveness on VJH 5
Figure 1.3 Comparison of Effect sizes across Studies of PT
effect on Soccer Specific Sprint Distances.
6
Figure 2.1 Jump Height Calculation 13
Figure 2.2 Rate of Force Development Calculation 13
Figure 2.3 Diagram of 5-0-5 COD drill 14
Figure 2.4 20 meter Sprint (5 meter acceleration) testing set
up
14
Figure 2.5 Cohen’s d calculation of Effect Size 16
Figure 2.6 Correctional equation for ES in low sample size
studies
17
Figure 3.1 Baseline and Post Intervention 5m Acceleration
Speed.
21
Figure 3.2 Baseline and Post Intervention 20 meter Sprint
Speed
22
Figure 3.3 Baseline and Post Intervention Change of Direction
Speed
22
Figure 3.4 Baseline and Post Intervention half back squat 1RM. 23
Figure 3.5 Intervention Effect Size on 5 and 20 meter sprint
speed
25
Figure 3.6 Intervention Effect Size for Change of Direction
ability
26

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List of Abbreviations
1RM One Repetition Maximum
BT Bilateral Training
BTG Bilateral Training Group
CG Control Group
CMJ Countermovement Jump
COD Change of Direction
CODA Change of Direction Ability
DJT Drop Jump Training
EG Experimental Group
EMG Electromyography
ES Effect Size
MS Maximal Strength
NSCA National Strength and Conditioning Association
PT Plyometric Training
RT Resistance Training
SLCMJ Single Leg Countermovement Jump
SP Sprint Performance
SSC Stretch Shortening Cycle
UT Unilateral Training
UTG Unilateral Training Group
VJH Vertical Jump Height

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Acknowledgments
At this point I would like to thank a number of people who have made this
project possible, through their support, advice and encouragement. Firstly, I
would like to thank my fellow researchers David Boor, Keiren Cruickshank and
Michael Watson, with whom it has been my pleasure to work alongside for the
duration of this project. Good luck with your futures lads, you will all be missed.
In addition I would like to acknowledge the Applied Sport and Exercise Science
lecturing team, who have supported me through my development, providing me
with 4 brilliant years of education. Special mention must go to Dr. Katherine
Burgess, who as my project handler and personal tutor has guided and
supported me immensely throughout this piece of work, and indeed all four
years of university, for which I am extremely grateful.
Thanks must also go to the participants who sacrificed their time to undertake
this project, for which I am extremely grateful, particularly when considering the
interest and passion with which you all carried yourselves throughout. Special
mention must also go to Simon Hall in this regard, who as technical services
officer was always on hand to assist with equipment set up and technical
difficulty, making the running of this project far easier in the process.
Thanks must also go to Andrew Maclaren, whose interest in the project and
advice throughout were much appreciated.
Furthermore, a special thanks must go to my mother Kathleen, father Michael
and sister Claire. Your unconditional love and support throughout this degree
and in particular this year has meant a very great deal to me, and without which
none of this would have been possible.
Lastly, I would like to thank my partner Chloe, whose love, support and sacrifice
throughout my time at university have not gone un-noticed or un-appreciated. I
dedicate this work to you.

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Abstract
Continual increases in professionalism within sport have led to a heightened
understanding of the importance of training specific to the requirements of
competition. Soccer has been identified as a sport which is primarily unilateral in
its nature, but given the limited understanding regarding the effects of training
in this manner on certain performance aspects, it is possible that it is largely
under-utilised with this population group. The purpose of this study therefore,
was to establish and compare the effects of unilateral and bilateral combined
resistance and plyometric training on soccer related fitness.
A between groups repeated measures study design was implented, with nine
collegiate mens soccer players randomly allocated to a unilateral training group
(n=3), bilateral training group (n=3) or control group (n=3). All participants
were assessed using unilateral and bilateral countermovement jumps, as well as
20 meter sprint speed, 5-0-5 change of direction ability and bilateral half back
squat one-repetition maximal lift, either side of a six week training intervention.
This required the experimental groups to carry out one session per week of
training specific to their discipline, but which shared comparable movement
patterns and muscle loading requirements.
Following the intervention, both experimental groups attained improvements
across all variables, with all but a few of these improvements being signifcant
(p<0.05) in relation to the changes observed in the control group. In addition,
the results indicated that the unilateral training groups post intervention
improvements were larger than those of bilateral training group in movements
which are unilateral in nature, although at time this differences did not reach
statistical significance.
The findings of this study tentatively indicate the value of training specificity,
and imply that when aiming to improve the unilaterally dominant movements of
soccer performance, the replacement of some bilateral training exercises with
unilateral alternatives has the potential to produce more significant
enhancements. However, further research is required in this field to attain more
confident findings, primarily through the use of a larger sample of participants,
and longer intervention period.

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1- Introduction
1.1 Background
Professional soccer has changed dramatically in recent times, with increased
financial investment causing a heightened professionalism as teams compete for
more valuable accolades. (Stolen et al., 2005; Norton and Olds., 2001; Maughan
and Gleeson., 2010). This is perhaps most evident in the form of specialist
training, to the point that the best teams across the world 30 years ago had
fitness levels comparable to some of the lowest ranked professional clubs today
(Stolen et al., 2005; Bush et al., 2015).
The main reason for these fitness enhancements is enhanced understanding
when designing training, recovery and nutritional intake for athletes, with
several key principles for effective conditioning dictating the planning and
execution of training in the modern game (Gamble., 2013). One such principle is
specificity (Kraemer et al., 2002) which describes the degree to which training
overloads a bodily system used in the sport, and in the manner most
comparable to the way which it will be required in competition (Baechle and
Earle., 2008). The importance of this principle is made clearer still by the
indication that little or no progression is observable in systems not adequately
engaged by training (Gamble., 2013).
As a result, an abundance of literature has strived to identify the specific
movement patterns and fitness demands of soccer, allowing coaches to plan
more effective training (Stolen et al., 2005). One key aspect of soccer specific
fitness identified is sprint performance (SP) over short distances (Fletcher.,
2009). Ten percent of all movements in soccer take this form, with short sprints
occurring every 90 seconds, which according to literature have a significant
impact on the outcome of a match (Mohr, Krustup and Bangsbo., 2003;
Bangsbo, Norregaard and Thorsole., 1991). Also identified as important is
vertical jump height (VJH) (Rampinini et al., 2007) because its execution affects
the outcome of games (Matsuda et al., 2014; Arnason et al 2004). Change of
direction ability (CODA) has been deemed to be of importance (Reilly, Bangsbo
and Franks., 2000; Reilly et al., 2000; Chaouachiet al., 2012). This is well
evidenced by Stolen et al (2005) who note the vast majority of the 1500
movementsin an average soccer game are off-ball, and therefore reactive in

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response to opponents and team mates (Rampinini et al., 2007). Finally,
considering the strong correlations observed in literature between each of these
variables and maximal leg strength (MS), it could be argued this too is a key
performance indicator with regards to soccer (Wisloff et al., 2004; Ronnestad et
al., 2011; Chaouachiet al., 2012). As a result of these findings, an abundance of
literature has been published regarding methods of improving these key
performance variables.
1.2 Review of Literature
The following section reviews previously published literature regarding the
effects of resistance and plyometric training individually and when combined on
the performance variables relevant for soccer performance outlined above,
followed by a comparison of the effect of carrying out such training bilaterally
and unilaterally.
1.2.1 Resistance Training
Resistance training (RT), is most simply defined as a type of physical activity
designed to increase muscle fitness by applying resistance external to the body
to a movement involving a specific muscle or group thereof (ACSM., 2013). The
relative improvements in MS following RT have been reported in an array of
studies, and are portrayed in figure 1.1 (e.g. Los-Arcos et al., 2014; Bogdanis et
al., 2011; Helgerud et al., 2011; Keiner et al., 2014).

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A strength of these studies, which are summarised in appendix 1, is their use of
a half back squat one-repetition maximum (1RM) to assess strength, based on
research recommending it to be both valid and relevant to soccer movement
because of its restricted depth (Chelly et al., 2009). These findings are
unsurprising, given the significant increases in strength RT is capable of due to
neural and physiological adaptations it causes within muscle (Baechle and Earle.,
2008). However, increases are significantly larger in studies using sets,
repetitions and loads which fall under the strength training category of RT
(ACSM., 2013). This is particularly well evidenced by Bogdanis et al. (2013)
when comparing the efficacy of strength and hypertrophic training for soccer
performance. This findings is of particular value to coaches because of the
significant increases in mass hypertrophic training produces, which can limit
power production and therefore force applicability to sports specific movement
(Baechle and Earle., 2008).
Regarding VJH, consistent improvements of 4-6% are visible following heavy RT
interventions in a selection of studies (Helgerud et al., 2011; Los-Arcoset al.,
2014; Shalfawi et al., 2013), which is consistent with comparable literature
which examined similar interventions on participants out with the field of soccer
(Stone et al., 1981; Stowers et al., 1983; Baker., 1994). A shared strength of
these studies, summarised in appendix 1, is the inclusion of back squats in the
Figure 1.1 - Relative Improvement in Maximal Leg Strength following RT intervention in soccer
players. STG=Strength Training Group; HTG=Hypertrophic Training Group; VS=Vertical Strength;
VHS=Vertical Horizontal Strength; *p=0.05.

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respective training interventions, based on the conclusion in literature this
particular exercise is significantly more effective than alternatives such as leg
press when developing VJH, which allows researchers to better understand the
value of the training modality in question (Sylvester et al., 1982).
In terms of SP, previous studies using soccer players of varying ability levels
have demonstrated improvements of 1.6-6% following heavy RT (Sander et al.,
2013; Helgerud et al., 2011; Keiner et al., 2014; Wong et al., 2010). It is a
strength of these studies, summarised in appendix 2, they have monitored sprint
ability over 30 meters or less given the finding by stolen et al (2005) that 96%
of sprints in soccer are of comparable distance, increasing the validity of these
authors findings. However, one study carried out by Shalfawi et al. (2013) found
RT ineffective for improving SP. This limited effect may be due to the timing of
the intervention falling in the competitive season, in which research suggests
athletes suffer a dip in fitness, as training volume severely lessens (Ronnestad,
Nymark and Raastad., 2011). The overall success of these interventions however
has been proposed to be due to the extremely high force generation it develops,
which is necessary when accelerating to overcome inertia (Gamble., 2010; Lentz
and Hardyk., 2005).
Finally, regarding CODA, RT has been deemed ineffective in an array of studies
(Fry et al., 1991; Cronin et al., 2003; Tricoli et al., 2005). This limited effect is
potentially because of the limited transference of vertical force production to the
horizontal plane in which most COD movement takes place (Brughelli et al.,
2008), as is implied by the findings of the above articles, in which all
interventions used vertically oriented exercises such as the back squat, and no
exercises focused on horizontal force generation.
1.2.2- Plyometric Training
Plyometric Training (PT) refers to exercises which aim to develop muscle power
capabilities, involving an initial eccentric loading phase, followed by a brief pause
(or amortization phase) and finally a rapid concentric contraction, with the
stretch shortening cycle (SSC) used to generate force (Saez De Villarreal et al.,
2009; Potach and Chu., 2008).

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As visible in figure 1.2, studies have found improvements in VJH following PT
intervention, for example Tricoli et al (2005), Herrero et al (2006) and Holcomb
et al (2006), with effect sizes varying from d=0.46 to d=0.86. From these
studies and others similar to them, which have been summarised in full in
appendix 3, it can be seen that the method of PT impacts on the degree of effect
observable following intervention. An example of this comes from the
improvements obtained when using a combination of different jumping
protocols, as was done by Markovic et al. (2007; Effect Size (d)=0.92), and
Drop Jump training (DJT) as used by Matvulj et al. (2001; d=1.42) compared to
countermovement jump training, which Dvir (1985)found provided less
significant improvement. The reason for the higher effect of combination PT is
potentially down to the multitude of different training stimuli the SSC is exposed
to, including fast SSC provided by bound like activity, and isolated concentric
contractions provided by activity such as squat jumps. This would imply future
interventions should include a combination of jumps, including primarily drop
jumps, when one of the goals of training is VJH improvement.
Figure 1.2 - Forest Graph of PT intervention effectiveness on VJH

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Furthermore it is visible in figure 1.3 that studies aiming to improve SP over
soccer relevant distances, for example Saez De Villarreal et al. (2008), Meylan et
al. (2009) and Salonikidis et al. (2008), have found effects varying from
insignificant to large.
A potential reason for the variation in effect observable in these studies, a full
summary of which can be found in appendix 4, comes from the exercises
implemented. For example, the study carried out by Markovic et al. (2007)
involved a combination of jumps, all of which focussed on vertically oriented
movements, and found minimally significant improvements (d=0.2), while
Impellizzeri et al. (2008) used bounding movements, and found improvements
of a very large significance (d=1.01). This is potentially explained by the
proposal by Young (1992) that bounding movements are highly effective for
sprint training because they are similar in nature to the movements required in
sprinting.
Less literature has been published examining the effects PT has on CODA,
however one study (Malisoux et al., 2006) which has aimed to establish its effect
in this regard found a very large effect size (d=2.1) when testing with the T-test
and following a combination of vertical and horizontal jumps. However, caution
must be taken interpreting this result because of the studies inability to match
experimental groups in terms of fitness at baseline, which potentially limits the
studies validity by making results appear to be more or less significant than they
Figure 1.3 - Comparison of Effect sizes across Studies of PT effect on Soccer Specific Sprint
Distances. Adapted from Saez de Villarreal, Requena and Cronin (2012).

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are (Brughelli et al., 2008). A potential justification for the effect of PT is that it
accurately reflects the ground reaction forces, muscle stiffness and eccentric
loading required for an efficient COD, with the conclusion of the review stating
PT is one of the most efficient methods of COD improvement for this reason.
In terms of strength gains following PT, studies found moderate–large (d=0.57
to 1.0) effect size following intervention (Fatouros et al., 2000; Lyttle et al.,
1996), but have all concluded these improvements are notably smaller than
those attained when PT was combined with additional forms of training, as is
also suggested to be the case in a comprehensive meta-analysis (Saez de
Villarreal et al., 2010) of twenty-five intervention based studies of PT effect on
strength.
1.2.3- Combined Resistance and Plyometric Training
This refers to interventions in which both RT and PT are provided to participants
concurrently. With regards to effect on VJH, Adams (1992) found this form of
training to be highly effective, increasing absolute jump height by over 7
centimetres more than either training method in isolation. These findings are
reflective of those in a systematic review of over 80 experimental groups finding
an average effect size for combined training (d=0.76), and only one of 0.65 for
PT alone (Saez de Villarreal et al., 2012).
With regards to SP, it was concluded in a meta-analysis of intervention studies
that PT combined with RT was less effective with regards to improving SP than
PT alone, albeit this difference was concluded to be insignificant (Saez de
Villarreal, Raquena and Cronin., 2012). This could be largely due to the type of
resistance training provided in a number of these studies, in which components
of the training fell under the hypertrophic repetition frequency and intensities set
out by the ACSM (2013) (Siegler et al., 2003; Lyttle et al., 1996; Fry et al.,
1991), thereby limiting the transference of any increased strength to sport
specific movement, as highlighted in section 1.1.
In terms of CODA, research regarding the effects of traditional RT and PT in
combination is limited (Brughelli et al., 2008). Furthermore, this limited research
has yielded largely contrasting findings, with a study by Fry et al. (1991) finding
a significant decrease in CODA (3.6%), and another by Faigenbaum et al. (2007)
concluding that CODA improved by 3.5%, despite the studies using interventions

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of comparable length and content. A potential explanation for this variance
comes from the variance in assessment method between the tests, given the use
of the T-test by Fry et al. and pro-agility shuttle time by Faigenbaum and
colleagues. This is based on the small inter-test correlations with regard to
agility assessment, proposed to be due to the wide ranging types of COD
movement and the different elements thereof assessed by different protocols
(Little and Williams., 2005). Additionally, Brughelli et al. (2008) stated in review
that COD movements are highly sports specific, the effects of combined RT and
PT on COD using a soccer specific assessment, such as the 5-0-5 test (Mirkov et
al., 2008), warrants further research.
In summary, the combination of PT and RT is an effective method of improving
the results each form has on VJH, as well as SP and potentially CODA, although
this remains unclear. A possible reason for this comes from the previously
suggested ability of RT to enhance muscle force production, and of PT to
improve the rate at which this force can be applied, as well as its applicability to
the movementsunder assessment (Kyrolainen., 2005; Kukric., 2012; Saez de
Villarreal et al., 2013), which in turn would imply when aiming to improve these
variables, future interventions should implement a combination of RT and PT to
be optimally effective.
1.2.4- Unilateral versus Bilateral Training
Bilateral training (BT) consists of exercises in which the applied resistance is
shared between both limbs working concurrently (Zatsiorsky and Kraemer.,
2006), and it is this form of training that is the key component of the majority of
traditional RT and PT training interventions (McKurdy et al., 2005).
The alternative to this form of practise is unilateral training (UT), wherein each
limb is trained individually. Previous literature suggests significant benefits can
be attained through this form of training (Luiz et al., 2013), with a potential
reason for this coming from the training’s ability to lessen the ‘Bilateral Deficit’
which describes the lesser force producible bilaterally compared to that
achievable as a combination of each limb individually (Pinto et al., 2012;
Khodiguian et al., 2013). Primarily, UT is used in high level sport as an
assistance exercise (McCurdy et al., 2005), potentially explaining the limited
research regarding its effect on performance variables (McCurdy et al., 2005).

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This limited research uses participants from an array of backgrounds including
physical education students (McCurdy et al., 2005) rugby (Fisher and Wallin.,
2014) and handball players (Jansson., 2013) and finds certain notable
similarities and contrasts to BT effects in relation to the fitness variables
discussed throughout this review. Firstly, it has been suggested UT in the form
of PT only (Delcore et al., 1998; Makaruk., 2011) and PT combined with RT
(McCurdy et al., 2005) can provide equal improvements in VJH to BT in
participants of a range of ability levels. Additionally to this, the above studies
found a significant difference in single leg jump improvement (+2.68cm in the
case of McCurdy et al (2005)), in favour of the UT group, suggesting this form of
training is capable of improving a players single leg jump height notably, without
limiting bilateral performance.
In terms of SP, while moderately significant correlations have been found
between bilateral VJH and SP (Chamari et al., 2005; Kukolj et al., 1999; Young,
Hawkin and McDonald., 1996), it has been concluded by a number of studies
(McCurdy et al., 2010; Nesser et al., 1996; Maulder, Bradshaw and Keogh.,
2006) that unilateral VJH correlated significantly more so with SP (-0.71 in the
case of McCurdy et al (2010)). These studies share the strength that they have
used interventions in which the unilateral and bilateral training groups carry out
interventions in which the movement patterns and muscle loading are
comparable, which allows for a valid and accurate comparison of the efficacy of
the training, and would indicate the significant value of UT when improving
soccer relevant SP.
In terms of CODA, there is a distinct lack of literature regarding the effects of UT
(Fisher and Wallin., 2014). A potential reason for the scarce evidence on this
topic comes from the fact that much research carried out in this area has gone
un-published, as observed by Sheppard and Young (2006) in review. From the
limited research though, notable conclusions have been reached. Initially,
studies observed that muscles which show far higher levels of activation when
exercised unilaterally are vital to the execution of effective COD (Young, James
and Montgomery., 2002; Young and Farrow., 2006). However, with no
intervention directly establishing the effects carrying out such unilateral
movementsrepetitively had on CODA, this was theoretical. Following these
findings, a range of studies observed significant improvement in CODA in team

10
sport athletes following a PT intervention containing of combined BT and UT
(Vaczi et al., 2013; Thomas et al., 2014; Meylan and Malatesta., 2009).
However, the aim of these studies was not to establish UT effect in comparison
to BT, and therefore with a lack of UT and BT experimental groups (EG), the
effects of UT alone remained unclear.
Latterly, Fisher and Wallin (2014)and Ramirez-Campillo et al. (2015a)
compared UT and BT effectiveness on CODA in physical education students and
soccer players respectively, with the finding that UT had a moderate to very
large positive effect size on COD, while BT was relatively ineffective, adding to
the evidence that UT is largely superior to BT for COD ability. However, Fisher
and Wallin (2014) did not test force production or MS of the legs at any point,
and in the absence of such data, the physiological reason behind UT’s superiority
remains unclear. Furthermore, the lack of any RT in the intervention
implemented by Ramirez-Campillo et al. (2015a) suggests, given the findings
above in section 1.3, that the effects attained could potentially have been more
significant still.
1.3- Research Aim and Hypothesis
In summary, given the evidence presented above regarding the effects of UT on
MS, SP and VJH, as well as the suggested unilateral nature of CODA, it is
possible that it is a highly beneficial method of training for sports in which these
are key performance indicators, such as soccer, considering the sport is
primarily unilateral in nature (Jones et al., 2012). However, given the lack of
comparative research between the two methods using soccer players as
participants in which a combination of RT and PT is implemented, and the limited
generalisability of findings regarding training effectiveness from other sports
because of the variances in body mass and the effects this have on SP and
CODA (Arin, Jansson & Skarphage., 2012), this remains unclear.
The purpose of the current study was to:
1. Establish the effect of unilateral and bilateral lower body combined
resistance and plyometric training interventions on soccer specific
performance variables, and

11
2. Compare these forms of training to determine which would be more
effective for the improvement of each of key performance indicators
highlighted in the above introduction.
It was the hypothesis of the researcher that while both UT and BT would
positively impact on the soccer specific fitness variables under inspection, the
training most specific to the movements associated with the variable would be
the most influential in their improvement.

12
2- Methodology
2.1- Experimental Design
In order to address the research question, a between groups repeated measures
design was implemented, with participants randomly allocated to one of the
experimental conditions, following suggestion this design is both valid and
reliable when aiming to establish intervention effect (Rubin and Babbie., 2009).
This design involved testing all participants twice, with the EG’s (Unilateral
Training Group (UTG) and Bilateral Training Group (BTG)) completing a six week
intervention between testing days, and the Control Group (CG) carrying out
regular training only.
2.2- Participants
Participants were randomly sampled from a local university mens soccer team to
minimise selection bias (Salkind., 2010). Inclusion criteria consisted of a
minimum of 2 years experience playing at collegiate level or similar, which
served the purpose of standardising the populations ability level to increase
study validity (Rubin and Babbie., 2009). Additionally, participants were required
to have a minimum of 12 months RT experience and have been injury free for in
excess of 6 months, to mirror the previously suggested criteria for an ‘advanced
athlete’ (Rhea and Alderman., 2004; Baechle, Earle and Wathen., 2008), which
was deemed neccessary given the highly demanding nature of intervention
exercises (Potach and Chu., 2008). In terms of exclusion criteria, participants
results were not included if they failed to attend 80% of intervention sessions, or
either of the testing days, following the negative impact failing to meet this
adherence rate has been suggested to have on study validity (Hoos et al.,
2012).
A sample of 9 students meeting the above criteria were accepted for the study
(Age=21.47 years(+1.26); Height=181.03cm(+6.93);Mass=78.89Kg(+7.06)),
and were briefed in full through an information sheet, before giving informed
consent and filling out a phyical activitity readiness questionnaire prior to study
commencement (Appendicies 5 and 6).

13
2.3- Testing Protocol
Baseline and post-intervention testing sessions took place in a single day with
participant clothing standardised (Winter et al., 2007). Two familiarisation trials
preceeded the recorded attempts to lessen the learning effect commonly seen
when participants are tested using measures they are unfamiliar with (Petersen
et al., 2015). Testing took place in the same order as each variable is discussed
below, to limits the negative impact tests have those subsequent (Harman and
Garhammer., 2008).
Initially, height was recorded using a stadiometer and weight with digital scales.
This was carried out with participants being encouraged to stand upright and
breathe naturally, as recommended in guidelines for recording (ACSM., 2013),
detailed in full in appendix 7. Following this, a standardised warm up (appendix
8) was carried out, based on recommendation that it improves performance and
minimises injury risk (Jeffreys., 2007).
VJH was assessed using the countermovment jump (CMJ), because of its
relevance in soccer (Wisloff et al., 2004). These jumps were initially completed
unilaterally for each leg (SLCMJ), then bilaterally (McKurdy et al., 2005), with
vertical ground reaction force recorded using a portable force platform
(Accupower, AMTI, Watertown, Massachusetts, USA). The data from this was
then used to attain VJH and rate of force development (RFD), using the
equations in figure 2.1 and 2.2 respectively, which were suggested to be highly
valid and reliable by Moir (2008).
Figure 2.1- Jump Height Calculation, where g=gravitational acceleration (9.81ms-2) and t=Time in
Air.
Figure 2.2- Rate of Force Development Calculation. Δ=Change.

14
For all jumps, three trials were recorded with 10 second rest intervals (Read and
Cisar., 2011) and no arm swing permitted, to isolate leg extensors (Lees,
Venrenterghem and De-Clercq., 2004).
Next CODA was tested using the 5-0-5 test illustrated in figure 2.3. The protocol
for this test, visible in appendix 9, had participants sprint 15 meters, before
completing a 180° turn and sprinting 5 meters back, with the last and first 5
meters of these runs the recorded time (Tanner and Gore., 2013). Three trials
were performed with three minure rest intervals (Plisk., 2008) and times
recorded using gates (Brower timing systems, Draper, Utah).
Thirdly, MS was tested using the half back squat 1RM. This was carried out using
the National Strength and Conditioning Association (NSCA) protocolfor 1RM
assessment. This protocol, a full version of which is included as appendix 10,
involved gradual increases in load with strategically prolonged rest periods, and
is proposed to be the gold standard measure of assessment for reliability and
safety (Baechle, Earle and Wathen., 2008).
Lastly, SP was assessed over 5 and 20 meter distances (Stolen et al., 2005)
using timing gates positioned as shown in figure 2.4, and participants starting 1
meter behind the first gates to avoid starting the timer accidentally (Green et
al., 2010). Three trials were recorced, with three minute rest intervals (Plisk.,
2008).
Figure 1.3- Diagram of 5-0-5 COD drill (Tanner and Gore., 2013).

15
2.4- Intervention
Intervention sessions followed by the BTG and UTG, which are outlined in full in
appendicies 11 and 12 respectively, included a combination of lower body
resistance and plyometric exercises with comparable movement patterns and
loading, for example bilateral drop jumps versus unilateral drop jumps, and
lasted approximately 60 minutes per session. All exercises were selected based
on the previously successful comparison of UT and BT when exercises were
similar in this regard (Fisher and Wallin., 2014; McCurdy et al., 2005), and
following suggestion all were relevant to the movements in soccer (Baechle,
Earle and Wathen., 2008; Gatz., 2009). All RT sets, repetitions and intensities
fell under the guidleines for strength training proposed by the NSCA (Baechle
and Earle., 2008) and participant intensities were determined using the
regression equations Wong et al (2010) demonstrated to be valid. Plyometric
jumps took place first, following the recommendations of Baechle and Earle
(2008), and from boxes of a standardised height used succeessfully in previous
comparison of UT and BT (Fisher and Wallin., 2014). Intensities for all exercises
were increased at the mid-point of the intervention, to avoid a limiting training
effectivness (Baecle and Earle., 2008).
2.5- Data Analysis
The Statistical Package for Social Sciences (SPSS, v.20) was used for all analysis
(Hicks., 2004). Both EG’s post intervention changes were analysed using the
Mann-Whitney U test (Mann and Whitney., 1947) to establish the significance of
differences in realtion to the CG, given its suggested reliability (Nachar., 2008).
This process was then repeated comparing the change in performance between
Figure 2.4- 20 meter Sprint (5 meter acceleration) testing set up.

16
the EG’s in cases when both showed signifcant differences to the control, to
determine is significant differences in effect existed. Non-parametric analysis
was prefered to parametric alternatives because of their requirement that data
be normally distributed (Hicks., 2004), which cannot be guarenteed in research
using small samples (Whitley and Ball., 2003). Furhermore, post intervention
effect sizes (ES) were attained using the Cohen’s D equation detailed below in
figure 2.5 (Cohen., 1988), to allow researchers to establish the extent to which
the intervention was was responsible for any changes observed (Nakagawa and
Cuthill., 2007).
Relative change in performance was used for this calculation following
recommendation that this allows an increased chance of identifying changes and
accurately interpreting their significance than absolute change in performance
settings (Richeldi et al., 2012), with CG ES calculated using baseline and post
intervention averages and standard deviations. Finally, given that low sample
sizes negatively effect the reliability of ES values (Hedges and Olken., 1985) the
correctional equation visible in figure 2.6 was used in an attempt to limit the
degree to which this would impact on study validity, and this value used as the
ES for all data collection (d).
Figure 2.5– Cohen’s d calculation of Effect Size (Cohen., 1988). d=ES; X1=Relative Change in
Performance of Experimental Group; X2=Relative Chance in Performance of Control Group;
s=Pooled Standard Deviation; n1=Number of Participants in Experimental Group; n2=Number of
Participants in Control Group; s1=Standard Deviation of relative change in Experiment Group;
s2=Standard Deviation of Relative Change in Control Group.

17
Figure 2.6- Correctional equation for ES in low sample size studies. Adapted from Hedges and
Olken (1985). ES=Effect Size; g=ES; n1=Number of participants in group 1; n2=Number of
participants in group 2.

18
3.0- Results
Initially, baseline to post-intervention changes across all groups will be
presented, followed by a comparison of the effect of each training intervention.
3.1- Performance Variables
3.1.1- Vertical Jump Height
VJH and RFD at both baseline and post intervention for all jumps and training
conditions is portrayed in table 3.1. Both the UTG and BTG demonstrated
significant increases in their CMJ VJH (8.23%, U=0.000, p=0.05, d=1.02 and
13.86%, p=0.05, d=1.71 respectively) in relation to the CG (1.6%, d=0.09).
Left leg SLCMJ height increased significantly in the UTG (23.48%, p=0.05,
d=1.74) and the BTG (15.03%, U=0.000, p=0.05, d=1.21) relative to the
changes in CG height (1.1%, d=0.04). The right leg SLCMJ heights attained
significantly increased in the UTG (11.26%; U=0.000; p=0.05, d=1.02) and by
9.62% in the BTG (U=0.000, p=0.05, d=1.27) in relation to the CG change
(3.37%, d=0.08).
The BTG demonstrated significant improvements in CMJ RFD (14.95%;
U=0.000; p=0.05; d=1.57) in relation to the CG (1.98%; d=-0.04), and while
the UTG also demonstrated improvements (6.76%; U=3.000; d=0.32) they
were insignificant (p=0.655). Left leg SLCMJ RFD was significantly improved by
both the UTG (10.73%;U=0.000; p=0.05; d=1.4) and BTG (4.56%; U=0.000;
p=0.05; d=1.29) in relation to the CG (-1.64%; d=-0.01). In terms of right leg
SLCMJ RFD, the UTG significantly improved (17.44%; U=0.000; p=0.05;
d=0.83) in relation to the CG (0.46%; d=-0.05), while the BTG also improved
(16.96%; U= 3.000; d=0.41) albeit insignificantly (p=0.655).

19
Table 3.1- Baseline and Post Intervention Vertical Jump Heights. m=Meters; SD=Standard
Deviation; UTG=Unilateral Training Group; BTG=Bilateral Training Group; CG=Control Group;
SLCMJ=Single Leg Countermovement Jump; RFD=Rate of Force Development; n.s-1=Newtons per
second; *=Significant Change (p=0.05).
Jump Variable Baseline
Mean(SD)
Post Intervention
Mean(SD)
Countermovement
Jump Height (m)
UTG 0.33(0.04) 0.35(0.04)*
BTG 0.35(0.02) 0.40(0.01)*
CG 0.35(0.03) 0.35(0.04)
Left SLCMJ Height
(m)
UTG 0.23(0.02) 0.29(0.01)*
BTG 0.23(0.04) 0.26(0.04)*
CG 0.23(0.03) 0.23(0.04)
Right SLCMJ (m)
UTG 0.23(0.01) 0.25(0.01)*
BTG 0.20(0.01) 0.22(0.01)*
CG 0.21(0.03) 0.22(0.02)
Countermovement
Jump RFD (n.s-1)
UTG 2225.58(276.77) 2372.97(344.85)
BTG 3380.30(547.58) 3868.64(502.41)*
CG 2567.98(646.82) 2617.88(656.45)
Left SLCMJ RFD
(n.s-1)

20
UTG 3013.53(1366.72) 3383.37(1706.28)*
BTG 3105.71(844.95) 3242.50(860.04)*
CG 3810.26(646.31) 3876.37(718.21)
Right SLCMJ RFD
(n.s-1)
UTG 2485.77(367.71) 2907.72(466.46)*
BTG 2881.36(1412.90) 3120.15(703.21)
CG 4654.68(1498.91) 4669.20(1473.07)

21
3.1.2- Sprint Speed and COD
Both the UTG and BTG decreased their 5m sprint speed (figure 3.1) significantly
(-7.62%, U=0.000, p=0.05, d=1.62; and -2.06%, U=0.000, p=0.05, d=1.24
respectively) in relation to the control group (0.1%, d=0.024). Additionally, the
UTG decrease in time was significantly larger than that of the BTG (p=0.05). In
terms of 20 meter sprint speed (Figure 3.2), the UTG time was significantly
decreased (5.17%, U=0.000, p=0.05, d=2.12) in relation to the change in CG
(0.6%, ES=0.256) while the BTG observed an insignificant (U=1.000, p=0.127)
decrease of 2.14%. COD speed, portrayed in figure 3.3, significantly decreased
in both the UTG (6.48%, p=0.05 U=0.000, d=3.03) and BTG (3.28%, U=0.000,
p=0.05, d=2.66) in relation to the CG (0.5%, ES=0.096).
Figure 3.1- Baseline and Post Intervention 5m Acceleration Speed. Significant Differences found in
Unilateral and Bilateral Training Groups compared to Control Group (p=0.05) and Unilateral
Training Group compared to Bilateral *p=0.05.

22
Figure 3.3- Baseline and Post Intervention Change of Direction Speed. Significant Differences
found between both Unilateral and Bilateral Training Groups compared to Control Group Post
intervention *p=0.05.
Figure 3.2- Baseline and Post Intervention 20 meter Sprint Speed. Significant Differences found in
Unilateral Training Group compared to Control Group *p=0.05.

23
3.1.3- Maximal Strength
Figure 3.4 portrays baseline and post intervention values for the Half Back squat
1RM across all training groups. The UTG significantly increased their 1RM by
8.38% (SD=1.49, U=0.000, p=0.046, d=2.25) in relation to the changes in CG
strength (1.19%, ES=0.024) while the BTG average increase was also significant
(15.59%, SD=7.59, U=0.000, p=0.046, d=1.08).
Figure 3.4- Baseline and Post Intervention half back squat 1RM. Significant Differences found
between both Unilateral and Bilateral Training Groups compared to Control Group Post
intervention. *p=0.05

24
3.2– Comparison of UT and BT Effect
3.2.1– VJH, RFD and MS:
Table 3.2 displays the intervention effect sizes of both EG’s and the CG for all
jumps and maximal strength variables. There were no significant differences in
the degree of effect between EG’s for the CMJ or SLCMJ on either leg (U=1.000-
3.000, p=0.127-0.513) or for the Half Back Squat (U=2.000, p=0.127).
However, with regards to RFD, there were significant differences in the
effectiveness of the training interventions for the CMJ, as well as left and right
leg SLCMJ’s (U=0.000; p=0.05).
Table 3.2-Intervention Effect Sizes of both Experimental Groups for VJH and MS data.
CMJ=Countermovement Jump; SLCMJ=Single Leg Countermovement Jump, 1RM=1 Repetition
Maximum; EG=Experimental Groups; *p=0.05; **p=0.046.
Intervention Effect Sizes for Both Experimental Groups
Performance
Variable
Unilateral
Effect Size
Bilateral
Effect Size
Control
Group
Effect Size
Between
EG’s p-
value
CMJH 1.02* 1.71* 0.09 0.127
SLCMJH Left 1.74* 1.21* 0.04 0.127
SLCMJH
Right
1.02* 1.27* 0.08 0.513
CMJ RFD 0.32 1.57* -0.04 0.05*
Left leg
SLCMJ RFD
1.42* 1.29* -0.01 0.05*
Right Leg
SLCMJ RFD
0.83* 0.41 -0.05 0.05*
Half Back
Squat 1RM
2.25** 1.08** 0.02 0.275

25
3.2.2- Sprint Speed
The ES of the UT and BT interventions, as well as the CG, on 5m and 20 meters
sprint times are presented in figure 3.5. The UTG 5 meter SP was improved
significantly more so than the BTG (U=0.000, p=0.05). This was similar over 20
meters, with the UTG attaining significant decreases in average time (U=0.000,
p=0.05) while the BTG’s changes were insignificant (U=0.000, p=0.127).
Figure 3.5- Intervention ES on 5 and 20 meter sprint speed. *=Significant difference in effect
between groups (p=0.05)

26
3.2.3- Change of Direction Ability:
Figure 3.6 demonstrates the ES on CODA attained in the UTG, BTG and CG, in
which it was found that there was a significant (U=0.000, p=0.05) difference
between the changes in both
Figure 3.6- Intervention Effect Size for Change of Direction ability. *=Significant Difference in
effect between experimental groups (p=0.05)

27
4- Discussion
The purpose of this study was to establish and compare the effect of unilateral
and bilateral combined resistance and plyometric training interventions on
physical performance variables relevant to soccer, with the research hypothesis
being that the training most specific to the movements associated to the
individual variable would be most effective. Our results indicate that both UT and
BT carried out concurrently with regular training are more beneficial than soccer
training alone. Furthermore, the above findings indicate the hypothesised
importance of training specificity to an extent, with the UTG improving more
than the BTG in all unilaterally dominant movements, albeit at times these
differences did not reach significance. This was also the case with the larger BTG
improvements in bilaterally oriented performance variables.
However, these results must be interpreted with caution, given the low sample
sizes used when attaining them, and the negative effects on reliability of
statistical findings such as effect size this has been suggested to have, even
after implementing correctional equations such as those detailed in the
methodology (Hedges and Olken., 1985). This is further evidenced by the
implication that to attain an acceptable statistical power of 0.8 (Murphy, Myors
and Wolach., 2014), and a moderately-high ES (d= 0.65), a sample of 30
participants per group would be required, in comparison to the 3 attained in this
study (Faul et al., 2007). This being acknowledged, there are several other
potential reasons for the current study’s findings, which are discussed below
using relative change in performance to better relate the findings to comparable
research, given the similar nature of the baseline findings in this study to that in
recent literature, as can be seen in appendix 13.
4.1– Jump Parameters
Both EG’s showed significant improvements in CMJ height compared to the CG
(8.2-23.4% vs 1.06-3.37%). This improvement is comparable to previous
studies of the effect of combined PT and RT on vertical CMJ height in soccer
players, in which improvements range from 3.2 to 18% (Faude et al., 2013; Los-
Arcos et al., 2014; Kotzamanidis et al., 2005), all of which were found to be
statistically significant (p<0.05). A potential reason for the variance here comes
from the performance level of participants. This is based on the suggestion that,

28
despite all studies using similar minimum required RT experience as the current
research, players of higher levels have superior fitness (Stolen et al., 2005) and
in turn, that this makes performance improvements harder to attain (Baechle
and Earle., 2008), as evidenced by the improvements of 3.2% and 6.4% observed
in the studies by Los-Arcos et al (2014), and Kotzamanidis et al (2005), in which
participants were professionals and national collegiate representatives
respectively.
Furthermore, as was hypothesised there was a potentially practical difference in
improvement in favour of the UTG for unilateral jumps and for the BTG for
bilateral jumps. This is again comparable to recent literature regarding the
difference in effect of unilateral and bilateral PT only (Ramirez-Campillo et al.,
2015a; Delcore et al., 1998) and PT combined with RT (McCurdy et al., 2005), in
which similar differences were discovered. A potential methodologicalreason for
this difference in effect is the lack of time for participants to practise the jumps
out with their training modality before post-intervention testing. This is based on
the suggestion in a study of mechanical control and muscle strength on VJH
(Bobbert and Van Soest., 1994) in which it was suggested that for optimal
jumping performance, participants need to practise the movement with their
post-intervention muscle properties.
Potential physiological reasons for the difference in improvements attained
between groups in this study also exist, with the primary cause likely to be the
neuromuscular adaptations achieved by both forms of training. This is based on
the suggestion in literature that the improvements in stiffness, RFD, segmental
coordination and eccentric loading capabilities of muscle following RT and PT are
highly specific to the training the participant carries out (McCurdy et al., 2005;
Ramirez-Campillo et al., 2015a; 2015b; Adams 1992). Further support of this
comes from the increases in RFD found in the current research, in which
significant (p=0.05) differences in training effectiveness are visible for both the
CMJ and SLCMJ’s in favour of the BTG and UTG respectively, highlighting the
value of training specific to the movements required in competition, as
hypothesised.

29
4.2– Maximal Strength
Both the BTG and UTG significantly improved bilateral squat strength (15.5%
and 8.3% respectively). This finding is in agreement with recent comparable
studies on the effect of combined RT and PT on maximal strength, in which
improvements ranged from 8.6 to 51.7% (Helgerud et al., 2003; Maio-Alves et
al., 2010; Kotzamanidis et al., 2005). While the large variance in effect here is
likely due at least in part to the highly individualised potential for adaption from
short term strength training interventions (Sale., 2008), it may also be partially
caused by the number of sessions per week each intervention group underwent.
This is based on the implication that to be optimally successful an intervention
aiming to improve back squat 1RM must contain a minimum of two sessions per
week (Kraemer and Ratamess., 2004), which is supported by the current
research attaining a maximal improvement of 15% from one session a week,
while Helgerud et al. (2003) found larger improvements using three.
It was hypothesised that the BTG would improve their strength more so than the
UTG. While this was the case this difference was insignificant (p=0.275), with a
potential reason for this coming from the significant improvements attained by
the UTG in bilateral 1RM strength. While this may be considered surprising, a
number of studies comparing the effects of UT and BT have found similarly high
effects of UT on bilateral strength (McCurdy et al., 2005; Spiers et al., 2016;
Janzen et al., 2006), with a potential justification for this coming from the
distribution of resistance on working muscles in the single leg squat. This is
based on the implication by Hefzy et al (1997), that when carrying out a single
leg exercise with the front knee at approximately 100° flexion, up to 75% of the
load is on this leg, which the researchers proposed, due to the significantly
higher intensity required in the working leg despite the lower absolute load,
made this method of training similarly effective to bilateral strength training.
4.3– Sprint Speed
Both EG’s in the current study attained improvements in both 5 and 20m sprint
speed (2.06%-7.62%), with all of these except the improvement in BTG 20m
sprint being statistically significant. This may be considered surprising given the
lack of horizontally oriented exercises in either intervention, and the suggestion
in an abundance of literature that these are required to improve SP over this

30
distance (Adams et al., 1987; Fry et al., 1991; Wilson et al., 1993). However,
comparable studies have discovered similar improvements using only vertically
oriented PT, (Thomasian., 2015; Rimmer and Sleivert., 2000), proposing that
these exercises are adequately effective because of their ability to elicit higher
force related adaptation than horizontally directed exercises, while still
maintaining a degree of movement specificity. Further support of this comes
from the comparable findings of the current research with recent literature
regarding the impacts of vertical and horizontal PT (Rimmer and Sleivert.,
2000), and combined PT and RT (Ford et al., 1983; Ronnestad et al., 2008) on
5-20 meter SP, which found effect significances ranging from small to large
(d=0.13 to 0.93).
It was hypothesised that the UTG would attain significantly larger improvements
in performance over both distances than the BTG, which was the case (p=0.05).
This is contradictory of recent studies comparing UT and BT effect on SP using
RT only (Speirs et al., 2015) in which no significant differences were observed,
and PT only (Fisher and Wallin., 2014), in which BT was considered significantly
more beneficial. A reason for these contrasting findings may come from the
indication in literature that combined RT and PT are more effective that RT alone
when improving sprint speed (Saez de Villarreal, Raquena and Cronin., 2012),
potentially justifying the lack of difference in effect between EGs in the study of
Speirs et al (2015). Furthermore, it is a common finding that novice participants,
such as the ones used in the study of Fisher and Wallin (2014), have a higher
capacity for improvement, making comparing results to those attained by
advanced athletes challenging (Baechle and Earle., 2008).
Furthermore, a potential reason for the significantly higher effect of the UT may
be the neuromuscular adaptations attained from the intervention, given the
significant improvements in unilateral RFD discovered in CMJ ability in the
current research, and the importance of RFD with regards to acceleration ability
(Fletcher., 2009). Another potential reason for the superior improvements here
however, comes from the implication in literature that one of the primary ways
in which sprint speed can be improved is through a reduction of time spent in
the stance phase, thus increasing stride frequency (Murphy et al., 2003). This
supports the difference in improvement attained in the current study, given that
the main method of minimising stance phase time is suggested to be efficient

31
force absorption, principally achieved through enhanced activation of the hip
stabiliser muscles and that these are more efficiently trained by UT (McCurdy
and Connor., 2003). This finding is reflective of a cross sectional study regarding
unilateral MS and linear SP in collegiate soccer players, in which it was found
that such strength correlated highly (r= -0.64) with 20 meter SP, supporting the
findings in the current study that UT is significantly beneficial when improving SP
(Arin, Jansson & Skarphage., 2012). Therefore and as hypothesised, the
difference in SP improvement in the current research was supported by the
training principle of specificity, given the findings above in relation to BT and UT
effect, and the suggestion in literature that sprinting is a unilateral movement
(McCurdy and Connor., 2003). Furthermore, it has been suggested that high
level sprinters endure compressionalforces of up to 6.5 times body weight
during the stance phase (Brand and Crowninshield., 1981). Based on this, as a
form of training which enhances activation of the muscles responsible for
absorbing this force, UT may be of more significant benefit than BT not only for
performance, but also for injury prevention in the case of sprinting, although it
was beyond the scope of the current study to establish this.
4.4- Change of Direction Ability
Both EG’s attained significant improvement (3.28% to 6.48%) in CODA in
relation to the change in the CG following their respective interventions. Previous
studies comparing the effects of PT (Meylan and Malatesta., 2009) and PT
combined with RT (Maio-Alves et al., 2010) have found wide ranging results,
from a highly significant decrease in performance (3.6%; d=0.76; Fry et al.,
1991) to comparable improvements to those obtained above (-3.6%; d=2.1;
Malisoux et al., 2006). However, caution must be taken when analysing the
variances of effect in the above literature, given the different tests used to
assess CODA. This is based on the small inter-test correlations observed in
literature regarding COD assessment (Brughelli et al., 2008) with a notable
example being the small correlation (r=0.2) between the 5-0-5 used in the
current study, and the Illinois test employed by the study by Meylan and
Malatesta (Draper and Lancaster., 1985).
It was hypothesised that UT would yield significantly higher improvements in
CODA than would BT. As discussed above in the results, this was the case

32
(p=0.05), which is contradictory of a recent comparable study (Speirs et al.,
2015) in which BT was found to be more effective than UT, albeit insignificantly.
Caution must be taken when comparing these studies to the current research
however, because of their use of rugby players as participants, and the large
difference in body mass between rugby and soccer players of a comparable level
to those in the current study (Arin, Jansson & Skarphage., 2012). This makes
comparison of findings challenging because of the high level of importance
placed on acceleration ability in effective COD, and the impact that mass has on
acceleration, since it is primarily determined by the degree of force an athlete
can produce, divided by their mass (Lockie et al., 2011).
Other studies of UT and BT have discovered a comparable differences in
effectiveness in favour of their respective UTG’s, ranging in significance from
moderate to large (Fisher and Wallin., 2014; Ramirez-Campillo et al., 2015a). A
possible reason for the superior improvements attained by the UTG in this
regard comes from the contrasting muscle adaptation achieved by both training
modalities, given the superior RFD improvements attained by the UTG in
unilateral CMJ, and the proposed importance this has when determining
acceleration ability (Brughelli et al., 2008). Another potential physiological
explanation for these results comes from the suggestion that effective COD
requires high levels of force production in the hip stabiliser muscles and that this
is more effectively trained through UT (Brughelli et al., 2008; Ayotte et al.,
2007). This is further evidenced by the limited activation of these stabilising
muscles during bilateral squats (Neuman and Cook., 1985; McCurdy and
Conner., 2003) and insignificant relationships found between bilateral squat
strength and CODA in published literature (Chaouachi et al., 2009; Markovic.,
2007). Contrastingly, significant correlations exist between unilateral MS and
CODA (r= -0.63; Arin, Jansson & Skarphage., 2012), highlighting the significant
value of training specificity when looking to achieve improvements in CODA, and
implying that unilateral exercises achieve this more so than do bilateral.
Furthermore, given the implication that COD movementsgenerate high levels of
force in the lower extremity joints, increasing the risk of injury, and that training
which improves the strength of the hip stabilising muscles responsible for the
absorption of this force, it could be argued that the superior effects of UT in
relation to CODA serve to limit injury risk as well as improve performance

33
(Alentorn-Geli et al., 2009). However, given that the current study is limited by
its lack of unilateral squat 1RM testing and EMG of muscle activation, it was
beyond the scope of this research to confirm this is the reason for larger
improvements observed following UT.

34
5– Conclusion
As well the limited sample size and methodological omissions discussed in
section 4, there are certain limitations in the current research which may have
impacted on findings. Firstly, as a result of the research design the UTG were
exposed to a training volume double that of the BTG. As acknowledged in
comparable research, this could have serve as a possible explanation for the
higher improvements in some of the performance variables (Fisher and Wallin.,
2014), meaning, it should be a priority of future research to adopt a design in
which training volumes are equal for each EG, to better understand the
difference in effect of each training protocol.
Another limitation of the current research is that while it was a requirement of all
participants to maintain their usual training schedule, neither this or nutritional
intake was monitored throughout the intervention period. Considering the
implication within literature that both training volume and quality of nutritional
intake impact on the potential effectiveness of resistance training, the lack of
monitoring and control of these factors could explain a degree of the variability
in intervention effect (Kerksick et al., 2008). Given that this limits the
comparability of the training protocols, future research in this field should
monitor these factors in order to better understand the exact reasons for
difference in performance enhancement following UT and BT.
However the current study also had a number of methodological strengths,
namely the use of highly valid testing measures of the performance variables
under inspection, as well as the standardisation of ability and fitness levels,
which enhances the generalizability of the findings. (Rubin and Babbie., 2009).
Additionally, this study adds to the scarce findings regarding the effects of
combined resistance and plyometric UT and BT in regards to soccer related
fitness, and is to the author’s knowledge the first study to compare such training
protocols using soccer players which has included an examination of COD
performance. This allows the current research to add to findings regarding the
effects of such training on these fitness aspects in general, as well as producing
preliminary findings which focus on the effects specific to soccer players, which
is of particular value given the strongly evidenced importance they have when

35
aiming to achieve optimal performance levels in such field sport athletes
(Rampinini et al., 2007).
The findings of this study indicate the value of training specificity, and as such
imply that when aiming to improve the unilaterally dominant movementswithin
soccer such as SP and CODA, the replacement of some commonly implemented
bilateral resistance and plyometric exercises with unilateral alternatives has the
potential to elicit larger performance gains. Additionally, the findings of this
study that UT improvements are insignificantly different to that of BT when
improving bilateral MS and VJH implies that such a replacement would not limit
the improvements attainable by the training intervention in this regard.
However, given the limitations of this study detailed throughout, it should be a
priority of future research to improve upon the work carried out above. This
should mainly be achieved through the adoption of a longer training intervention
and a sample size reflective of the required amount stated above to attain
suitable statistical power to achieve a more confident understanding of the
validity of findings attained. Additionally, forthcoming studies regarding the
comparison of effectiveness of these training modalities should include a method
of assessing unilateral MS, as well as EMG data from the muscles highlighted as
being instrumental in sprinting and CODA. This would allow for a clearer
understanding of the physiological reasons for UT’s superiority with regards to
unilateral performance enhancement, as well as the effect and difference therein
of each training modality with regards to injury prevention.

36
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54
7.0– Appendices
Appendix 1 – Table of review of Resistance Training Interventions and Maximal Strength/Vertical Jump Height
Authors
Name
Participants Intervention
Details
Intensity of
Resistance
Training
(SetsxReps)
Performance
Variable
Measured
Testing Method
Used
Results of Study
Bogdanis et
al 2011
20 Elite
Soccer
Players
10 in
Hypertrophy
Training
Group (H)
10 in
Maximal
Strength
Training
Group (S)
6 Weeks (Pre-
Season)
10-12 Regular
Sessions plus 3
sessions per
week of
Experimental
Group Training
Strength
Training Group
- 4x5@90%
1RM
Hypertrophy
Training Group
- 4x12@70%
1RM
Max Strength Half-squat strength
(1RM)
Half Squat 1RM:
S Group improved by 17.7%
H Group improved by 11.2%
Helgerud et
al 2011
21 Elite
Soccer
Players
One Group
Test –Retest
design
Concurrently
Training High
Intensity
Aerobic
8 Weeks (Pre-
Season)
2 sessions per
week plus
regular
training.
Strength
Training –
4x4RM
Jump Height Countermovement
Jump (CMJ)
CMJ improved by 5.2%
Maximal
Strength
Half Squat 1RM Half Squat improved by 51.7%

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