Chapter 6 BIOMECHANICS OF MOTION: PART I

Objectives  Describe muscle contraction  Describe the nervous control of muscle contraction  List the four functional groups of muscles  Discuss heat generated by muscle contraction affects performance.  Contrast aerobic and anaerobic metabolism during muscular contraction.  Name the types of muscle fibers and their function

Muscle Contraction  Any movement requires a coordination between brain, nerves, muscles and bones (figure 6 -1)  Action starts in the brain – receives stimuli (input)  Signal is sent through the spinal cord to  Efferent nerves to  Muscle – which causes action (i.e. joints to move)

Muscle contraction, cont’d  Message sent to joint proprioceptors to  Afferent nerves signal back to  Spinal cord to  Brain  Continuous cycle  Some signals do not go all the way back to the brain –  Go back to ganglia – where they are re-directed to muscle causing action. Reflexes

How muscles contract  Skeletal muscles are attached to bone  Voluntary – generally  Muscle bundle – muscle fiber – myofibril  Contraction takes place at the myofibril level - intracellular  When a muscle contracts: (figure 6 – 2)  Neurotransmitter Acetylcholine excites muscle cells  Releases Ca ions which bind to troponin  Frees up actin and myosin – which form bridges  Causing muscle contraction  When Ca levels drop – cycle is reversed and muscle relaxes

3 factors of force  Short periods of stimulation:  Calls for more Ca, elasticity of tendons and ligaments  Length of muscle when stimulated  Distance between actin and myosin filaments – long muscles  Number of actin and myosin filaments acting  Greater number of filaments – greater the force

Energy (figure 6 -3)  Provided by metabolic processes that produce ATP  Requires Oxygen - aerobic  When sufficient oxygen is not provided (anaerobic) the process produces lactic acid and ATP  Inadequate removal of lactic acid produces soreness and stiffness.

Muscle fibers  Type I  Slow twitch, (aerobic)  Used by slow/light activities  Uses carbohydrates, proteins or fats

Muscle fibers  Type IIa  Fast twitch fibers (aerobic)  Endurance, stamina  Uses carbohydrates, fats and proteins

Muscle fibers  Type IIb  Fast twitch fibers (anaerobic)  Speed or power fibers  Strenuous workouts  Use only carbohydrates  Examples:  American Quarter Horse – relatively high numbers of Type IIb fibers,  Arabian, Type I and IIa fibers

Muscle fatigue  Fatigue is generally an accumulation of waste products that cannot be transported away from the muscle. (lactic acid)  Recovery requires removal  Rub downs

Heat  By product of metabolism and muscle action  Removed by:  Sweating/evaporation  Air movement across body  Blood vessels closest to the skin expand  Allowing more blood to be cooled  In hot environments can be a relatively large shift  Fluid losses, sweating, metabolism  Potential loss of blood volume (i.e. plasma loss)  What do you see as a possible negative outcome?