Chapter 8, Part 2Properties of Muscle Fiber Types• Biochemical properties– Oxidative capacity– Type of ATPase• Contractile properties– Maximal force production– Speed of contraction– Muscle fiber efficiencyIndividual Fiber TypesFast fibers• Type IIx fibers – Fast-twitch fibers– Fast-glycolytic fibers• Type IIa fibers– Intermediate fibers– Fast-oxidative glycolytic fibersSlow fibers• Type I fibers– Slow-twitch fibers– Slow-oxidative fibersMuscle Fiber TypesFast Fibers Slow fibersCharacteristic Type IIx Type IIa Type INumber of mitochondria Low High/mod HighResistance to fatigue Low High/mod HighPredominant energy system Anaerobic Combination AerobicATPase Highest High LowVmax(speed of shortening) Highest Intermediate LowEfficiency Low Moderate HighSpecific tension High High ModerateComparison of Maximal Shortening Velocities Between Fiber TypesType IIxFig 8.11Histochemical Staining of Fiber TypeType IIaType IIxType IFig 8.12Fiber Types and Performance• Power athletes – Sprinters– Possess high percentage of fast fibers• Endurance athletes – Distance runners– Have high percentage of slow fibers•Others– Weight lifters and nonathletes– Have about 50% slow and 50% fast fibersAlteration of Fiber Type by Training• Endurance and resistance training– Early research• Cannot change fast fibers to slow fibers– More recent• Weight training– Can result in shift from Type IIx to IIa fibers (incomplete)– Toward more oxidative properties• Endurance training (rat)– Ten weeks, 90 min/day – Type IIx to Type IFig 8.13Age-Related Changes in Skeletal Muscle• Aging is associated with a loss of muscle mass– Rate increases after 50 years of age• Regular exercise training can improve strength and endurance– Cannot completely eliminate the age-related loss in muscle massTypes of Muscle Contraction •Isometric– Muscle exerts force without changing length– Pulling against immovable object– Postural muscles• Isotonic (dynamic)– Concentric• Muscle shortens during force production– Eccentric• Muscle produces force but length increasesFig 8.14Isotonic and Isometric ContractionsFig 8.14Speed of Muscle Contraction and Relaxation• Muscle twitch– Contraction as the result of a single stimulus– Latent period• Lasting only ~5 ms– Contraction • Tension is developed•40 ms– Relaxation•50 msFig 8.15Muscle TwitchFig 8.15Force Regulation in Muscle• Types and number of motor units recruited– More motor units = greater force– Fast motor units = greater force– Increasing stimulus strength recruits more & faster/stronger motor units• Initial muscle length– “Ideal” length for force generation• Nature of the motor units neural stimulation– Frequency of stimulation• Simple twitch, summation, and tetanusFig 8.16Fig 8.17Fig 8.18Relationship Between Stimulus Frequency and Force GenerationFig 8.16Length-Tension RelationshipFig 8.17Simple Twitch, Summation, and TetanusFig 8.18Force-Velocity Relationship• At any absolute force the speed of movement is greater in muscle with higher percent of fast-twitch fibersFig 8.19Force-Velocity RelationshipFig 8.19Force-Power Relationship• At any given velocity of movement the power generated is greater in a muscle with a higher percent of fast-twitch fibersForce-Power RelationshipFig 8.20Receptors in Muscle• Muscle spindle– Changes in muscle length– Rate of change in muscle length – Intrafusal fiber contains actin & myosin, and therefore has the ability to shorten– Gamma motor neuron stimulate muscle spindle to shorten• Stretch reflex– Stretch on muscle causes reflex contractionFig 8.21Muscle SpindleFig 8.21Receptors in Muscle• Golgi tendon organ (GTO)– Monitor tension developed in muscle– Prevents damage during excessive force generation• Stimulation results in reflex relaxation of muscleFig 8.22Golgi Tendon OrganFig