Skeletal Muscle State possible sources of fatigue Distinguish

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

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

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

Origins of Localized Muscle Fatigue Accumulation Theory of Fatigue: Lactic Acid and free H+ K+ NH 3 • 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: • Ca 2+-ATPase • myosin ATPase speed • aerobic capacity (mitochondria, myoglobin, blood supply, fatigue resistance) • anaerobic capacity (glycolytic enzymes)

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)