Biomechanics of Resistance Exercise

1. Biomechanics of Resistance Exercise Biomechanicsof ResistanceExercise EXSC STD. 13

2. STANDARD 13 Review the concepts of kinesiology and biomechanics from the Rehabilitation Careers course. Explain how joint and bone movement, body motion, and levers can have positive or negative effects on an athlete’s performance and development. In a presentation or speech intended for an audience of young athletes, describe the effects of overtraining on the musculoskeletal system, and relate the importance of adopting safe biomechanical practices when training.

3. Key Terms • anatomy: The study of components that make up the musculoskeletal “machine.” • biomechanics: The mechanisms through which these components interact to create movement.

4. Musculoskeletal System • Skeleton • Muscles function by pulling against bones that rotate about joints and transmit force through the skin to the environment. • The skeleton can be divided into the axial skeleton and the appendicular skeleton. • Skeletal Musculature • A system of muscles enables the skeleton to move. • Origin = proximal (toward the center of the body) attachment • Insertion = distal (away from the center of the body) attach-ment

5. Figure 4.1

6. Key Terms • agonist: The muscle most directly involved in bringing about a movement; also called the prime mover. • antagonist: A muscle that can slow down or stop the movement.

7. Musculoskeletal System • Levers of the Musculoskeletal System • Many muscles in the body do not act through levers. • Body movements directly involved in sport and exercise primarily act through the bony levers of the skeleton. • A lever is a rigid or semirigid body that, when subjected to a force whose line of action does not pass through its pivot point, exerts force on any object impeding its tendency to rotate.

8. Figure 4.2

9. Key Term • first-class lever: A lever for which the muscle force and resistive force act on opposite sides of the fulcrum.

10. A First-Class Lever (the Forearm) • Figure 4.3 (next slide) • The slide shows elbow extension against resistance (e.g., a triceps extension exercise). • O = fulcrum; FM = muscle force; FR = resistive force; MM = moment arm of the muscle force; MR = moment arm of the resistive force. • The depiction is of a first-class lever because muscle force and resistive force act on opposite sides of the fulcrum.

11. Figure 4.3

12. Key Term • second-class lever: A lever for which the muscle force and resistive force act on the same side of the fulcrum, with the muscle force acting through a moment arm longer than that through which the resistive force acts.

13. A Second-Class Lever (the Foot) • Figure 4.4 (next slide) • The slide shows plantarflexion against resistance (e.g., a standing heel raise exercise). • FM = muscle force; FR = resistive force; MM = moment arm of the muscle force; MR = moment arm of the resistive force. • When the body is raised, the ball of the foot, the point about which the foot rotates, is the fulcrum (O).

14. Figure 4.4

15. Key Term • third-class lever: A lever for which the muscle force and resistive force act on the same side of the fulcrum, with the muscle force acting through a moment arm shorter than that through which the resistive force acts.

16. A Third-Class Lever (the Forearm) • Figure 4.5 (next slide) • The slide shows elbow flexion against resistance (e.g., a biceps curl exercise). • FM = muscle force; FR = resistive force; MM = moment arm of the muscle force; MR = momentarm of the resistive force.

17. Figure 4.5

18. Musculoskeletal System • Anatomical Planes of the Human Body • The body is erect, the arms are down at the sides, and the palms face forward. • The sagittal plane slices the body into left-right sections. • The frontal plane slices the body into front-back sections. • The transverse plane slices the body into upper-lower sections.

19. Figure 4.10

20. Human Strength and Power • Basic Definitions • strength: The capacity to exert force at any given speed. • power: The mathematical product of force and velocity at whatever speed.

21. Key Term • concentric muscle action: A muscle action in which the muscle shortens because the con-tractile force is greater than the resistive force. The forces generated within the muscle and acting to shorten it are greater than the external forces acting at its tendons to stretch it.

22. Key Term • eccentric muscle action: A muscle action in which the muscle lengthens because the contractile force is less than the resistive force. The forces generated within the muscle and acting to shorten it are less than the external forces acting at its tendons to stretch it.

23. Key Term • isometric muscle action: A muscle action in which the muscle length does not change because the contractile force is equal to the resistive force. The forces generated within the muscle and acting to shorten it are equal to the external forces acting at its tendons to stretch it.

24. Joint Biomechanics:Concerns in Resistance Training • Back • Back Injury • The lower back is particularly vulnerable. • Resistance training exercises should generally be performed with the lower back in a moderately arched position. • Intra-Abdominal Pressure and Lifting Belts • The “fluid ball” aids in supporting the vertebral column during resistance training. • Weightlifting belts are probably effective in improving safety. Follow conservative recommendations.

25. Figure 4.15

26. Joint Biomechanics:Concerns in Resistance Training • Shoulders • The shoulder is prone to injury during weight training because of its structure and the forces to which it is subjected. • Warm up with relatively light weights. • Follow a program that exercises the shoulders in a balanced way. • Exercise at a controlled speed. • Knees • The knee is prone to injury because of its location between two long levers. • Minimize the use of wraps.

27. Joint Biomechanics:Concerns in Resistance Training • How Can Athletes Reduce the Risk of Resistance Training Injuries? • Perform one or more warm-up sets with relatively light weights, particularly for exercises that involve extensive use of the shoulder or knee. • Perform basic exercises through a full ROM. • Use relatively light weights when introducing new exercises or resuming training after a layoff of two or more weeks. • Do not ignore pain in or around the joints. (continued)

28. Joint Biomechanics: Concerns in Resistance Training • How Can Athletes Reduce the Risk of Resistance Training Injuries? (continued) • Never attempt lifting maximal loads without proper preparation, which includes technique instruction in the exercise movement and practice with lighter weights. • Performing several variations of an exercise results in more complete muscle development and joint stability. • Take care when incorporating plyometric drills into a training program.