Biomechanics of Skeletal Muscle (Ch 6) Objectives Identify the basic behavioral properties of the musculotendinous unit. Explain the relationships of fiber types and fiber architecture to muscle function. Explain how skeletal muscles function to produce coordinated movement of the human body. Discuss the concepts of muscle strength, power, and endurance from a biomechanical perspective.

Properties, structure and function of muscle Properties of muscle-tendon function Extensibility and elasticity Elastic and contractile components (Fig 6.2, p 147) Irritability and the ability to develop tension Structural Org of Skeletal Muscle (Fig 6.3 – 6.6) Motor Unit (Fig 6.7, p 151) Classification of Muscles by fiber architecture: parallel, pennate (F 6.11, p 155) by articulation (number of joints crossed) uniarticulate, biarticulate passive and active insufficiency

Passive insufficiency – due to inability of a multiarticular muscle to allow full ROM at both ends

Active Insufficiency – due to inability of a multiarticular muscle to generate force when shortened at one end

Electromyography and fiber type recruitment The motor unit and Electromyography (Figure from lab) motoneuron & all innervated fibers Muscle Fiber Types Slow twitch oxidative (SO), or Type I Fast twitch oxidative glycolitic (FOG), or Type IIA Fast twitch glycolitic (FG), or IIB Functional differences -Fig 6.10, p 152 Characteristics - Table 6.2, p 153 Selective recruitment of fiber types – size principle: SO FOG FG

Muscle Fiber Types

Recruitment proceeds from smallest fibers to largest (the size principle)

Skeletal Muscle Function Types of muscle contraction Concentric (muscle length is decreasing) Eccentric (muscle length is increasing ) Isometric (muscle length is constant) Roles assumed by muscles Agonist (prime and assistant movers) Antagonist Stabilizer Neutralizer Synergist

Biarticular muscle action and synergy

Application of force of muscular contraction Strength Amount of torque a muscle group can generate at a joint (related to physiological cross-sectional area) Endurance Resistance to fatigue Ability of muscle group to continue to repeat or sustain submaximal torque Fatigue Performance decrement Power Work rate Combination of strength and speed

Study Questions For Chapter 6 Biomechanics of Skeletal Muscle Self-study questions: Intro probs, p 173, #1,3,; Add prob, 174 p # 1