Biomechanics of Resistance Exercise Everett Harman, PhD, CSCS, NSCA-CPT chapter

Biomechanics of Resistance Exercise Everett Harman, PhD, CSCS, NSCA-CPT chapter www.phwiki.com

Biomechanics of Resistance Exercise Everett Harman, PhD, CSCS, NSCA-CPT chapter

Rogers, Chuck, Executive Producer has reference to this Academic Journal, PHwiki organized this Journal Biomechanics of Resistance Exercise Everett Harman, PhD, CSCS, NSCA-CPT chapter 4 Biomechanics of Resistance Exercise Chapter Objectives Identify the major bones in addition to muscles of the human body. Differentiate among the types of levers of the musculoskeletal system. Calculate linear in addition to rotational work in addition to power. Describe the factors contributing to human strength in addition to power. Evaluate resistive as long as ce in addition to power patterns of exercise devices. (continued) Chapter Objectives (continued) Recommend ways to minimize injury risk during resistance training. Analyze sport movements in addition to design movement-oriented exercise prescriptions.

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Section Outline Musculoskeletal System Skeleton Skeletal Musculature Levers of the Musculoskeletal System Variations in Tendon Insertion Anatomical Planes of the Human Body Key Terms anatomy: The study of components that make up the musculoskeletal “machine.” biomechanics: The mechanisms through which these components interact to create movement. Musculoskeletal System Skeleton Muscles function by pulling against bones that rotate about joints in addition to transmit as long as ce through the skin to the environment. The skeleton can be divided into the axial skeleton in addition to 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

Human Skeletal Musculature Figure 4.1 (next slide) (a) Front view of adult male human skeletal musculature (b) Rear view of adult male human skeletal musculature Figure 4.1 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.

Musculoskeletal System Levers of the Musculoskeletal System Many muscles in the body do not act through levers. Body movements directly involved in sport in addition to exercise primarily act through the bony levers of the skeleton. A lever is a rigid or semirigid body that, when subjected to a as long as ce whose line of action does not pass through its pivot point, exerts as long as ce on any object impeding its tendency to rotate. A Lever Figure 4.2 (next slide) The lever can transmit as long as ce tangential to the arc of rotation from one contact point along the object’s length to another. FA = as long as ce applied to the lever; MAF = moment arm of the applied as long as ce; FR = as long as ce resisting the lever’s rotation; MRF = moment arm of the resistive as long as ce. The lever applies a as long as ce on the object equal in magnitude to but opposite in direction from FR. Figure 4.2

Key Term mechanical advantage: The ratio of the moment arm through which an applied as long as ce acts to that through which a resistive as long as ce acts. A mechanical advantage greater than 1.0 allows the applied (muscle) as long as ce to be less than the resistive as long as ce to produce an equal amount of torque. A mechanical advantage of less than 1.0 is a disadvantage in the common sense of the term. Key Term first-class lever: A lever as long as which the muscle as long as ce in addition to resistive as long as ce act on opposite sides of the fulcrum. 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 as long as ce; FR = resistive as long as ce; MM = moment arm of the muscle as long as ce; MR = moment arm of the resistive as long as ce. Mechanical advantage = MM /MR = 5 cm/40 cm = 0.125, which, being less than 1.0, is a disadvantage. The depiction is of a first-class lever because muscle as long as ce in addition to resistive as long as ce act on opposite sides of the fulcrum. During isometric exertion or constant-speed joint rotation, FM · MM = FR · MR . Because MM is much smaller than MR, FM must be much greater than FR; this illustrates the disadvantageous nature of this arrangement.

Figure 4.3 Key Term second-class lever: A lever as long as which the muscle as long as ce in addition to resistive as long as ce act on the same side of the fulcrum, with the muscle as long as ce acting through a moment arm longer than that through which the resistive as long as ce acts. Due to its mechanical advantage, the required muscle as long as ce is smaller than the resistive as long as ce. A Second-Class Lever (the Foot) Figure 4.4 (next slide) The slide shows plantarflexion against resistance (e.g., a st in addition to ing heel raise exercise). FM = muscle as long as ce; FR = resistive as long as ce; MM = moment arm of the muscle as long as ce; MR = moment arm of the resistive as long as ce. When the body is raised, the ball of the foot, the point about which the foot rotates, is the fulcrum (O). Because MM is greater than MR, FM is less than FR.

Figure 4.4 Key Term third-class lever: A lever as long as which the muscle as long as ce in addition to resistive as long as ce act on the same side of the fulcrum, with the muscle as long as ce acting through a moment arm shorter than that through which the resistive as long as ce acts. The mechanical advantage is thus less than 1.0, so the muscle as long as ce has to be greater than the resistive as long as ce to produce torque equal to that produced by the resistive as long as ce. 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 as long as ce; FR = resistive as long as ce; MM = moment arm of the muscle as long as ce; MR = moment arm of the resistive as long as ce. Because MM is much smaller than MR, FM must be much greater than FR.

Figure 4.5 The Patella in addition to Mechanical Advantage Figure 4.6 (next slide) (a) The patella increases the mechanical advantage of the quadriceps muscle group by maintaining the quadriceps tendon’s distance from the knee’s axis of rotation. (b) Absence of the patella allows the tendon to fall closer to the knee’s center of rotation, shortening the moment arm through which the muscle as long as ce acts in addition to thereby reducing the muscle’s mechanical advantage. Figure 4.6 Reprinted, by permission, from Gowitzke in addition to Milner, 1988.

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Moment Arm in addition to Mechanical Advantage Figure 4.7 (next slide) During elbow flexion with the biceps muscle, the perpendicular distance from the joint axis of rotation to the tendon’s line of action varies throughout the range of joint motion. When the moment arm (M) is shorter, there is less mechanical advantage. Figure 4.7 Moment Arm Figure 4.8 (next slide) As a weight is lifted, the moment arm (M) through which the weight acts, in addition to thus the resistive torque, changes with the horizontal distance from the weight to the elbow.

Figure 4.8 Key Point Most of the skeletal muscles operate at a considerable mechanical disadvantage. Thus, during sports in addition to other physical activities, as long as ces in the muscles in addition to ten-dons are much higher than those exerted by the h in addition to s or feet on external objects or the ground. Musculoskeletal System Variations in Tendon Insertion tendon insertion: The points at which tendons are attached to bone. Tendon insertion farther from the joint center results in the ability to lift heavier weights. This arrangement results in a loss of maximum speed. This arrangement reduces the muscle’s as long as ce capability during faster movements.

Figure 4.16 (continued) Reprinted, by permission, from Harman, Johnson, in addition to Frykman, 1992. Key Point Specificity is a major consideration when one is designing an exercise program to improve per as long as mance in a particular sport activity. The sport movement must be analyzed qualitatively or quantitatively to determine the specific joint movements that contribute to the whole-body movement. Exercises that use similar joint movements are then emphasized in the resistance training program.

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