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Intro Muscle Strength Assessment.pptx

  1. Muscle Strength Assessment
  2. Muscular Strength The ability of a muscle group to develop maximal contractile force against a resistance in a single contraction. Muscular Endurance The ability of a muscle group to exert submaximal force for extended time periods.
  3. Concentric Force exerted by muscle or muscle group exceeds external resistance or load  Joint angle decreases  Muscle shortens Eccentric Isometric Contraction Types Braking mechanism to decelerate body segment movement (resist gravity)  Joint angle increases  Muscle lengthens Force exertion and external resistance equal  Static Joint angle  Static muscle length
  4. Isometric Contraction Both concentric and eccentric contractions are sometimes called isotonic (“iso,” same; “tonic,” tension). The term “isotonic contraction” is a misnomer because the tension produced by the muscle group fluctuates greatly even though the resistance is constant throughout the range of motion (ROM).
  5. The fluctuation in muscular force during isotonic contractions is due to the change in muscle length and angle of pull as the bony lever is moved, creating a strength curve that is unique for each muscle group. For example, the strength of the knee flexors is maximal at 160° to 170°. Isometric Contraction
  6. Isokinetic Contraction  Maximal contraction of muscle or muscle group at a constant velocity throughout entire range of motion (ROM).  Specialized machines control velocity of contraction and adjust external resistance to match the force produced at degree in the ROM.  Resistance is variable, velocity is constant) (Electromechanical devices vary the resistance to match the muscular force produced at each point in the ROM. Thus, isokinetic exercise machines allow the muscle group to encounter variable but maximal resistances during the movement.)
  7. Muscle Strength Assessment Tools
  8. Muscle strength is typically measured isometrically. This limits variability due to muscle length (sarcomere size) and movement ability Isometric strength = the maximum force exerted in a single contraction against an immovable resistance (i.e., maximum voluntary isometric contraction or MVIC)
  9. • Isometric dynamometer • Measures static grip strength • Advantages: easy protocol, portable, inexpensive, common testing method • Disadvantage: doesn’t equate well to performance, limited to 1 movement Grip Dynamometer
  10. Hand-Held Dynamometer • Isometric dynamometer • Measures isometric muscle strength in a variety of muscle groups and motions • Advantages: wide variety of tests can be done, portable, accurate data, better mimic common movements • Disadvantage: more tester error, errors due to site placement, more expensive
  11. Large Frame Dynamometer • Isometric dynamometer • Measures isometric muscle strength in one motion, but at varying joint angles • Advantages: very accurate data, isolates specific joint angles • Disadvantage: very expensive, not portable, requires space and user training
  12. Isokinetic Dynamometer • Isokinetic dynamometer • Contriols speed of joint movement and measures force throughout a joint range of motion. • Advantages: very accurate data, isolates joint angles for better data • Disadvantage: very expensive, not portable, requires space and user training
  13. Dynamic Strength • One-repetition maximum (1RM): maximum weight that can be lifted for one complete repetition of the movement • Advantages: Easy of use, movements are common to many subjects, comparable data available • Disadvantages: Trial and error, not precise data, machines differ
  14. Dynamic Endurance • Perform multiple reps with weight that is set submaximal load (%1RM) or set %body mass. • The YMCA (Golding 2000) and ACSM (2010)
  15. Issues with Muscle Assessment Tests
  16. Test/retest reliability is the biggest issue with muscle strength assessment
  17. Test/retest reliability issues