unit4 lecture1 how muscles cause movement physiological process myosin cross bridges pull actin sarcomere shortens develops tension pulls on bone attachment sites movement occurs only way muscle can cause movement to cause movement at specific joint muscle must cross joint have attachments on either side of joint movement roles of muscles describe muscle activity during a movement 1 agonist or prime mover muscle primarily responsible for causing movement ex quadriceps PM for knee extension 2 antagonist opposes particular movement of agonist antagonistic movements and muscles hip ex Flexion iliopsoas agonist gluteus maximus antagonist ex Extension gluteus maximus agonist iliopsoas antagonist 3 synergists muscles help another muscle synergy cooperative action neutralizer type of synergist heavy load some positions biceps synergist during fast supination or heavy load biceps cause elbow flexion and supination if we only want supination must neutralize flexion triceps neutralizes elbow flexion during supination movement role depends on movement situation triceps prime mover elbow extension antagonist during elbow flexion neutralizer during supination with extended elbow human body leverage system body functions in movement as a system of levers bones joints and muscles constitute lever system lever type of simple machine use to gain an advantage in force speed or range advantage able to do less and get more components of a lever system E effort force R resistance force Fulcrum E R force advantage move a greater force while applying less force using a simple machine neutralizes unwanted movements 2 joint muscle simultaneously causes motion at both joints but don t want 2 movements 2 kinds of force effort muscle balances pull of object resistance object pulls balance down distance called a moment arm moment arm perpendicular distance from fulcrum to line representing force moment arm of effort moment arm of resistance torque force is applied to move the lever causes body levers to move relationship between resistance torque and effort torque will determine how the muscle functions outcome is function of amount of force moment arm distance torque force x moment arm distance outcome is called torque resistance torque resistance force at some distance from fulcrum resistance torque resistance force x moment arm resistance ex resistance torque 10 x 6 60 in lb R MAR R x MAR 60 10 lbs x 6 in effort torque created by muscle pulling on bone to be moved effort torque effort force x moment arm effort ex effort torque 50 x 2 100 in lb E MAE E x MAE 100 50 lbs x 2 in example biceps curl 50 lb weight does resistance stay the same throughout motion MA distance MA longer greater torque MA shorter smaller torque types of muscle tension when muscle develops tension between its ends 1 of 3 things may happen compare effort resistance torques isometric and isotonic contractions develops tension without changing length important in postural muscle function and antagonistic muscle joint stabilization isometric muscle contraction isotonic muscle contraction tension while shortening concentric tension while lengthening eccentric 1 muscle tension is greater than resistance torque concentric contraction muscle shortens ex bicep curl upward movement constant tension shortened muscle only way muscle causes movement prime movers concentric tension 2 muscle tension is equal to resistance torque isometric contraction no shortening and no motion even though muscle is trying to cause movement muscle develops tension but does not shorten no movement resistance torque greater than muscle torque eccentric contraction muscle is lengthened while trying to shorten resistance torque wins ex bicep curl downward movement muscle lengthens while maintaining tension muscle acts as a brake to slow or control movement efficiency of contraction if the amount of energy used is the same eccentric greatest force produced resistance is doing work oxygen use lower isometric energy not used for shortening concentric least efficient least force produces energy used for shortening not available for producing tension isotonic tension means equal tension muscle would produce same amount of tension throughout ROM because of body lever system muscles rarely function isotonically classes of levers 3 first class fulcrum between effort and resistance second class resistance between effort and fulcrum move large resistance with less effort favors force effort MA always longer than resistance MA third class favors speed and range effort moves through less distance and at slower speed than resistance effort MA always shorter than resistance MA force disadvantage advantages of first class lever determined by length of moment arms effort MA longer favors force effort MA shorter favors speed and range human body levers most are third class levers few first class with speed and range advantage human body levers have a large force DISadvantage no second class levers in the body through ROM effort and resistance moment arms change muscle lab setting muscle twitch response to single brief threshold stimulus three phases time from stimulation to start of contraction latent period Ca 2 released troponin moves tropomyosin cross bridges attach etc period of contraction period of relaxation no force generated cross bridges release Ca pump working time from onset of contraction to peak tension actin is being pulled by myosin muscle twitch some muscles have very rapid twitch times some muscle twitches longer and slower graded contraction single muscle twitch lap phenomenon graded muscle responses variations degree of muscle contraction two ways 1 frequency of stimulus 2 stimuli in rapid succession 2nd twitch stronger than 1st called wave summation 2nd starts from partly contracted muscle left over Ca 2 frequency of stimulation increasing stimulation rate shorter relaxation time summation becomes greater eventually no indication of relaxation phase tetanus fused into smooth sustained contraction most voluntary muscle contraction are short term tetanic contractions smooth sustained contractions allow smooth controlled movements 2 strength of stimulus stronger stimulus recruits more motor units increases number of muscle fibers involved stronger contraction called multiple motor unit summation or recruitment treppe stimuli too far apart to cause wave summation each resulting contraction is stronger staircase effect treppe increased Ca 2 and heat basis for warm up