Chapter 20: Muscular Fitness and Assessment

Transcription

1 Chapter 20: Muscular Fitness and Assessment American College of Sports Medicine. (2010). ACSM's resource manual for guidelines for exercise testing and prescription (6th ed.). New York: Lippincott, Williams and Wilkins Copyright 2010 Wolters Kluwer Health Lippincott Williams & Wilkins

2 Principles of Muscle Function Muscle fiber recruitment Type I muscle fibers are primarily used during sustained endurance activities. Type II muscle fibers are generally recruited for higher intensity, poweroriented resistance exercises and shorter bouts of work. Muscular fitness assessments examine a person s ability to recruit a predominant fiber type and test for endurance, power, maximal force production, or combinations. Muscular force development Cellular voltage changes (action potentials) release calcium ions (Ca 2+ ) into the interstitial space. A positive voltage change stimulates cross-bridge formation and a power stroke between actin and myosin filaments, thereby shortening the sarcomere. Process is repeated in a progressive manner for individual muscle fibers.

3

4 Principles of Muscle Function Muscular force development Additional fiber recruitment leads to more cross-bridge formations and greater relative force production, ultimately achieving the maximum voluntary contraction (MVC). The number of fibers recruited is related to the strength and frequency of neurologic stimulus from a motor neuron, termed motor unit recruitment. Mechanics of force development See Figures 20-1, 20-2, and 20-3 for information. Each system combines three separate components: force application (muscular insertion), fulcrum or center of rotation (joint center), and resistance application (center of gravity), all applied along a lever arm (bone). Anatomic levers are primarily third class because the muscle insertion is commonly distal to the joint center and proximal to the resistance application.

5

6 Classes of Anatomical Levers Classes of Anatomical Levers. Class 1 (a), class 2 (b), and class 3 (c). F, fulcrum (joint centre); M, force generation (muscle); R, resistance (centre of gravity, external load). Anatomic examples are illustrated. Recall most human examples are class 3. (a) (b) (c)

7 Mechanical Representation of Force and Torque Mechanical representation of force and torque development in the elbow, where force M is muscular force generation in response to force W and force F. Distances indicated represent moments created by the bony lever of the forearm at various points relative to the joint fulcrum. Force J represents joint reaction force produced during muscular contraction

8 Force Component Vectors Force component vectors representing rotary force (red), stabilizing force (gray), dislocating force (black), and muscle force orientation (white). Note as muscle insertion angle changes from A (45 degrees) to B (90 degrees) to C (>90 degrees), force vectors shift properties from stabilizing/rotary, purely rotary, and dislocating/rotary, respectively

9 Skeletal Muscle Response to Resistance Exercise Resistance exercise is a single bout of variable resistance exercise. Resistance Training (RT) is a long-term program of progression and overload (i.e., progressive overload principle) with subsequent adaptation. Muscle fiber adaptation Strength gains associated with RT may be the result of hyperplasia or hypertrophy or a result of neurologic adaptations. Generally, strength gains after RT are attributable to increased fibre size rather than additional fibre production. Neurologic adaptations and muscular hypertrophy to strength enhancements are largely determined by age, training status, and genetic predisposition.

10 Relative roles of neural and muscular adaptation to strength training Sale. Med. Sci. Sport Exerc. 1988, 20(5 Suppl):S135-S145

11 RT-Induced Changes in Neural Function Aagaard, 2003, Exerc. Sport Sci. Rev. 31(2):61-67.

12 Skeletal Muscle Response to Resistance Exercise RT can help to reverse or attenuate the following: Loss of skeletal muscle (atrophy) is a natural physiologic response to disuse as a result of injury, immobilization, sedentary lifestyle, and/or certain disease processes that cause reduced muscle protein synthesis. Sarcopenia is common in elderly persons and patients suffering from chronic diseases or medical conditions, congestive heart failure, chronic obstructive pulmonary disease, and liver failure. Special population and safety considerations RT is beneficial for both men and women; those with cardiac disease, cancer, metabolic diseases, and pulmonary disease; and others. High-intensity RT appears to provide a cardioprotective effect in some populations. All individuals should avoid breath holding or the Valsalva maneuver during RT.

13 indicates values increase;, values decrease;, values remain unchanged; or, small effect; or, medium effect; or, large effect. From Williams M, Haskell W, Ades P, et al. Resistance exercise in individuals with and without cardiovascular disease: 2007 update: a scientific statement from the American Heart Association Council on Nutrition, Physical Activity, and Metabolism. Circulation. 2007;116:

14 Tissue Adaptation to Training Stimulus Tissue adaptation to training stimulus. Appropriate stress on muscle or connective tissue results in remodelling and stronger tissue. Overuse injury occurs when tissue continues to be trained and damaged without adequate remodelling time.

15 S. Bird, Doctoral Thesis 2006, School of Human Movement Studies, Charles Sturt University

16 S. Bird, Doctoral Thesis 2006, School of Human Movement Studies, Charles Sturt University

17 Muscular Fitness Assessment Muscular strength is defined as peak force developed during a maximal voluntary contraction (MVC). Strength and power are assessed for four main purposes: To quantify relative significance of strength and power for athletic events and other activities To identify deficiencies in muscular function so that serial improvements can be monitored (strength diagnosis) To evaluate the potential of individuals for particular athletic pursuits To assess the effects of training and rehabilitation programs Techniques and limitations Repetition maximum (see Boxes 20-2 and 20-3) Dynamometry can be used to asses isotonic, isoinertial, and isometric force generation capabilities. Ideally any testing should be reliable, reproducible, and accurate.

18 Repetition Maximum Prediction Equation Brzycki M. Strength testing: predicting a one-rep max from a reps-to-fatigue. Journal of Physical Education, Recreation and Dance. 1993;64(1):88 90

19 Repetition Maximum Testing Procedure 1. Complete a light warm-up with muscle groups to be tested 2. 1-minute rest period 3. Estimate and complete movement with a workload that will allow three to five repetitions to fatigue 4. 2-minute rest period 5. Estimate near maximum workload and complete set to fatigue 6. 2-minute rest period 7. Increase load progressively for one to three additional sets until maximum load completed for 1RM is achieved 8. If single repetition is failed, reduce load by 2.5% to 5% for upper-body or 5% to 10% for lower-body exercises 9. Reattempt 1RM Set is completed either when two to three repetitions are completed successfully or form is compromised during subsequent repetitions; 1RM must be completed, maintaining proper biomechanical form for the exercise. Retesting should be completed using identical procedures to ensure reliability of measures

20 Muscular Fitness Assessment Testing safety and equipment considerations Warm-up is recommended and serves to increase blood flow to primary muscles and connective tissues and may reduce the risk of injury during testing. Concentric lifting time of 3 to 5 seconds is appropriate, but note that exercise intensity and overload is greater during the eccentric phase of movement. Reliability of assessment The test-retest reliability of isokinetic, isometric, and isoinertial dynamometry is normally high. Considerations to improve reliability: Individual s athletic ability Instructions provided Recent bouts of exertion to fatigue Selected testing angles Postures Standardized testing environment These considerations apply to range-of-motion assessment also.

21

22 Clinical relevance and applications If testing is performance specific and sport oriented, it may be possible to reliably predict athletic performance in a competitive environment. Can compare against normative data (see Table 20-3) to determine ability versus similar individuals If normative data is not available, can compare relative to others or to a pretraining assessment Body stature and testing Differences in lever arm lengths, musculature. and other body type differences affect the force-generating capacity.

23 Technologic instrumentation Electromyography (EMG) is the study of motor unit activity in skeletal muscle and can be used to gather a large amount of muscle fiber related information. EMG requires a skilled technician and analysis for useful information. Computer-generated animations allow practitioners to design physical conditioning programs specifically for complex, dynamic, and high-velocity movements. There are a number of other biochemical and physiologic testing procedures that are complex and under constant development that can (or may in the future) help with muscular fitness/movement analysis and help to guide training and treatment.

24

25

26 Flexibility and Range of Motion (ROM) The joint s ability to pass through a given ROM without significant impingement or restriction is its flexibility. Measurement and assessment of flexibility and ROM is particularly useful in athletic training, rehabilitation, and conditioning settings. Assessment Devices include: Goniometers: assess simple joint ROM; portable, relatively easy to use, and inexpensive; measurements are highly reproducible Inclinometers: spinal and other complex movements Video analysis with digitization: accurate but expensive and time consuming to perform Sit and reach boxes: lower back and hamstring ROM; inexpensive, easy to use; can also be performed with just a tape measure (no box)

27 Flexibility and Range of Motion (ROM) Factors influencing reliability and validity American Medical Association suggests measuring three consecutive trials and averaging results. For accuracy consider: anatomic landmark identification, positioning and stabilization of body and device, consistency in technique and protocol, accurate recording of measures Stretching Goal is to alter tendon inflexibility to enhance joint ROM. Stretching routines should be developed specific to the desired goals (e.g., athletic performance, injury reduction, balance, etc.). Consider methods of stretching: Static Proprioceptive neuromuscular facilitation (PNF) Dynamic stretching Ballistic

28 Devices Used for Measuring Joint ROM. Left: Standard Goniometer The most common instrument used for measuring joint ROM is the twoarm goniometer Spinal and other complex movements, including supination, pronation, ankle inversion, and eversion, are difficult if not impossible to assess with a traditional goniometer. Such data are more accurately measured using an inclinometer. Inclinometers use a universal center of gravity to establish a starting point that remains constant from test to test

29 Average Range of Motion Estimates from the American Academy of Orthopedic Surgeons Joint Movement Average ROM (in degrees) Shoulder Horizontal flexion 135 Horizontal Neural abduction 170 Flexion 158 Extension 53 Internal rotation 70 External rotation 90 Elbow Flexion 146 Extension 0 Forearm Pronation 71 Supination 84 Wrist Flexion 73 Extension 71 Radial deviation 19 Ulnar deviation 33 Hip Flexion 113 Extension 28 Abduction 48 Adduction 31 Internal rotation /External rotation 45 Knee Flexion 134 Extension 0 Ankle Plantar flexion 48 Dorsi flexion 18 Foot Inversion 33 Eversion 18