EXSS 276 1st Edition Lecture 22 Outline of Last Lecture I. Skeletal Muscle FibersI. RecruitmentII. Fiber Types w/ a Whole MuscleIII. Distribution and Recruitments of Different Types of FibersIV. Types of Muscle ContractionV. Factors Affecting Force ProductionOutline of Current LectureI. Force ProductionVI. Frequency of StimulationVII. Energy for Muscle ContractionVIII. Muscle FatigueCurrent LectureI. Force Productiona. Muscle Lengthi. Impacts cross bridge interactionii. More interaction = more forceiii. Muscle and connective tissues have elastic properties1. Store energy when stretched; released during muscular activity iv. Length tension curve – optimal length is somewhere in the middlev. Length of muscle fibers1. Optimal overlap of thick and thin filamentsa. Produces greatest number of cross bridges and greatest amount of tension2. If muscle overstretched (past optimal length)a. Fewer cross bridges exist; less force produced3. If muscle overly shortened (less than optimal)a. Fewer cross bridges exist; less force producedb. Thick filaments crumpled by Z discs4. Normally, resting muscle length between 70-130% of the optimum5. Neither is an advantage (under-stretched vs. overstretched) b. Joint anglei. Force generated in muscle transferred to bone via tendon insertionThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.ii. Optimal joint angle maximizes force transmitted to bone (via # of cross bridges)c. Speed of actioni. Force-velocity curve1. Decrease force, increase velocitya. The lighter the load, quicker we can shorten muscle2. Increase load, decrease velocitya. Heavier load, slower we can shorten muscleIX. Frequency of Stimulationa. Twitchi. Latent period (2 ms)1. Calcium is released from SR2. Slack is being removed from elastic componentsii. Contraction period (10-100 ms)1. Filaments slide past each otheriii. Relaxation period (10-100 ms)1. Active transport of calcium back into SRiv. Refractory period (5 ms in skeletal; 300 in cardiac)1. Muscle can’t respond and has lost excitabilityb. Summationi. Wave summation: second stimulus applied before muscle has completely relaxed after previous stimulus; results in increased strength of contractionc. Tetanusi. Incomplete: sustained muscle contraction that permits partial relaxation between stimuliii. Completed: sustained contraction w/ no relaxation between stimuliX. Energy for Muscle Contractiona. Muscle metabolism – production of ATP in muscle fibersi. Muscle uses ATP at a great rate when activeii. 3 sources of ATP production1. Creatine phosphate (CP)2. Anaerobic cellular respiration/glycolysis3. Aerobic cellular respirationb. Creatine Phosphatei. Excess ATP within resting muscle used to form creatine phosphateii. CP 3-6 times more plentiful than ATP w/in muscleiii. 15 sec (used for 100m dash)iv. Quick breakdownv. Passing P groupc. Anaerobic cellular respirationi. ATP produced from glucose breakdown into pyruvic acid during glycolysisii. If no oxygen, pyruvic acid converted to lactic acid, which diffuses into the bloodiii. 30-40s of maximal activity (200m run)d. Aerobic cellular respirationi. Requires oxygenii. ATP for activities >30siii. Provides 90% of ATP energy if activity lasts more than 10 minutes XI. Muscle Fatiguea. Inability to contract after prolonged activityb. Factors that contributei. Central fatigue is feeling of tiredness and desire to stopii. Insufficient release of ACh from motor neuronsiii. Depletion of CPiv. Decline of calcium w/in SR/ Ca leaking out of SRv. Insufficient O2 or glycogenvi. Buildup of lactic acid and