Chapter 6BIOMECHANICS 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?