Skeletal Muscle • State possible sources of fatigue • Distinguish the different muscle fiber types.
Central Peripheral Afferent Feedback Psychological Motivation Neural Transmission Muscular Transmission • AP Propagation • AP Propagation Muscular contraction • cross-bridge interference Origins of Localized Muscle Fatigue SITES OF THE SOURCES OF FATIGUE
ATP Origins of Localized Muscle Fatigue Depletion Theory of Fatigue: Fatigue results from the depletion of metabolites necessary for energy production Glucose Oxygen ADP or CP Reaction Enzymes
Decreases membrane excitability • Decreases Ca++ affinity for Troponin • Inhibits Aerobic Metabolism • Decreases the release of Ca++ • Obstructs glycolysis Origins of Localized Muscle Fatigue Accumulation Theory of Fatigue: Lactic Acid and free H+ K+ NH3
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)
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)