John Orchard Adjunct Associate Professor, Sydney Medical School, University of Sydney. - Hamstrings are most susceptible to injury during the late stance phase of sprinting

1. Hamstrings are most susceptible to injury during the early stance phase of sprinting
John Orchard, MBBS BA MD PhD FACSP FACSM FASMF FFSEM (UK)
Ass Prof, School of Public Health, University of Sydney
October 13, 2014
6th MuscleTech Network
Workshop, Barcelona
Delivered remotely
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2. When do muscles strain?
Muscle strains are amongst the most common injuries in football players and sprint athletes although little is proven about the time of occurrence of strains
Strains can be recreated in the laboratory, but in vivo occur so rapidly that the forces resulting in strain are very hard to assess
An implanted force transducer into hamstring tendon could measure forces in the various phases
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3. Clinical occurrence of strains
Hamstring
Football, sprints
Full pace
?swing ?stance
Quadriceps
Soccer, ARF
Kicking
?ball/swing/ ground
Calf
Tennis, squash
Take-off
Ground contact
Groin
Soccer, ARF
Change direction
Ground contact
Upper limb
clinically rare
tackling
Player contact
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4. Laboratory occurrence of strains
Strain model simulated in lab by over- stretch of isolated rabbit muscle (i.e. not rabbit muscle during a running activity)
Strain in this fashion occurs at musculotendinous junction (MTJ)
Real life: MTJ (most common) as well as tendon, muscle belly, myofascial
Presumably similar pathology, but in real life activities (e.g. sprinting) maximal range of motion of muscle groups is not reached
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5. When do muscles strain?
In real life activities, highest range of motion (stretch) generally occurs during swing phases (most susceptible phase)
However, highest external joint moments generally occur during ground phases
Does low(er) force in a high(er) risk phase cause the injury or high(er) force in a lower risk phase cause the injury?
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6. Forces on muscles and joints
Change of movement of a joint is determined by a sum of net muscle moment and net external moment
Mann (1981): muscle moments for knee flexion and hip extension were both highest in the early ground phase of sprinting
He concluded that this is when hamstring strains occur (initial contact)
Recent supported by Takashi Ono (biomechanics, Waseda Uni, Tokyo)
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7. Clinical paradigm
Teaching of Garrett et al. suggests that 2- joint muscles strain when undergoing an eccentric contraction
This suggests that hamstring muscles may strain in late swing phase (eccentric phase) rather than early ground contact (when already contracting concentrically)
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8. Forces responsible for strain
Leiber et al. (1993, JAP) showed that in the laboratory strain model, muscle strain damage correlated with external force applied rather than over activity of the muscle.
Suggests that Ralph Mann’s explanation of muscle strain pathogenesis was wrong, but phase (early stance) could be correct
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9. Wrong for right reasons?
However, muscle force correlates strongly with degree of stretch (i.e. eccentric contractions are much stronger than concentric contractions)
Therefore maximal net muscle moments probably coincide with maximal external moments in the other direction
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10. Eccentric or isometric?
Kurokawa et al. (JAP, 2001) have shown that there is a phase after eccentric contraction where musculo-tendinous unit as a whole is isometric
However, using realtime U/S of gastroc during jumping have shown that initially the muscle component contracts while the tendon component continues to lengthen
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11. Kurokawa et al. sequences
Muscle
Tendon
M/T Unit
Eccentric contraction
Lengthening
Lengthening
Isometric contraction
Lengthening
Lengthening
Concentric contraction
Lengthening
Constant
Concentric contraction
Shortening
Shortening
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12. Joint Moments
Stance
Swing
Peak Hip
Extension*
Peak Knee
Flexion*
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13. Quad strains - dominant kicking leg in football codes
Quadriceps strains more common in dominant kicking leg (RR 2.13, 95% CI 1.59-28.6)
Hamstring and calf fairly evenly distributed
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14. Quadriceps strains?
Anecdotal description of occurrence during ball contact
But, this would clearly be when shortening
Why wouldn’t triceps strain when serving or spiking in volleyball if ball contact can strain a shortening muscle?
Could quadriceps strain occur in back- swing or even ground contact?
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15. Type of kicks at risk for QdStr
Running kicks rather than standing kicks
Rare on kicking out from goal, or kicking after a mark (Aust football) or goalkeepers (soccer)
Very rare in punters in NFL
Rare in goalkickers in rugby codes
Related to speed of running rather than distance of kick
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16. Biomechanics: calf strains
Occur during push-off phase
Presumably ground contact
Video – one calf strain available of Steve Waugh from StumpCam
Occurs during second step of take-off towards end of ground contact cycle
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17. Before and after frames
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18. Biomechanics: calf strains
Occur during ground contact phase
Occur during close to full range (increased stretch) but not maximal range
Close to an isometric phase (moving from eccentric to concentric)
Occur during push-off (acceleration) of second step
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19. Biomechanics: hamstring
Hamstring strains are likely to occur during overstriding when close to maximum speed and trying to maintain speed
Again near maximum stretch but not at maximal length
Again moving from eccentric to concentric
?Start of ground contact
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20. Biomechanics: quadriceps strains
Can occur when running (slowing down) not just kicking
Related to dry weather rather than wet weather (?ground contact)
Mechanism: perhaps caused by under- striding of kicking leg during final step (when slowing down) before the kicking motion
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21. Can force in a tendon be directly measured?
Answer – Yes; but it has only been done to date by one research group and for Achilles (calf) and patella (quadriceps) tendons in taking off and landing.
Finni T. et al. “In Vivo…” Eur J Appl Physiol (2000). 83: 416-26 and Eur J Appl Physiol (2001). 85: 170-76
Forces in tendons in swing phases negligible compared to ground contact
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22. Forces in PT/AT (arrow = stance/swing phase change)
Take-off
Landing
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23. Conclusion
Lower limb muscles prob. strain during stance phase, when external joint moments (& muscle reactive moments) are high
These instances probably are in situations of relative overstretch (but not maximum)
In gait cycle hamstring probably early stance (?phase of eccentric tendon/concentric muscle if an overstride)
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