Skeletal Muscle State possible sources of fatigue Distinguish the different muscle fiber types.

SITES OF THE SOURCES OF FATIGUE Origins of Localized Muscle Fatigue SITES OF THE SOURCES OF FATIGUE Central Afferent Feedback Psychological Motivation Peripheral Neural Transmission Muscular Transmission Muscular contraction AP Propagation cross-bridge interference

Depletion Theory of Fatigue: Origins of Localized Muscle Fatigue Depletion Theory of Fatigue: Fatigue results from the depletion of metabolites necessary for energy production ATP Glucose Oxygen ADP or CP Reaction Enzymes

Origins of Localized Muscle Fatigue Accumulation Theory of Fatigue: Lactic Acid and free H+ K+ NH3 Decreases membrane excitability Decreases Ca++ affinity for Troponin Decreases the release of Ca++ Obstructs glycolysis Inhibits Aerobic Metabolism

Skeletal Muscle Fiber Types innervating nerve is primary determinant of fiber type during development a motor unit is composed of homogenous fibers all human muscles contain mixture of three general fiber types slow twitch (ST, oxidative, red) fast twitch (FTa, fast-oxidative, red) fast twitch (FTb, glycolytic, white)

Time Course of Contributions from Different Energy Sources fast twitch glycolytic (white) slow twitch oxidative (red) Oxidative

Fiber Type Characteristics Performance characteristics affected by: Ca2+-ATPase myosin ATPase speed aerobic capacity (mitochondria, myoglobin, blood supply, fatigue resistance) anaerobic capacity (glycolytic enzymes) Be able to contrast the physiological characteristics of the three fiber types. Also, be able to explain how each of the bulleted items affects performance characteristics.

Muscle Movements ‘Not all force results in movement.’ Isotonic - (same force), muscle fibers create a force that moves a load. Muscle shortens or lengthens. Isometric - (same distance), muscle fibers create changing force but does not move a load. Muscle length doesn’t change. Tendon collagen stretches out. concentric – develops tension while shortening eccentric – develops tension while lengthening *(most muscle actions are a combination of these)