Muscle Anatomy 101 Pt2
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Transcript of Muscle Anatomy 101 Pt2
Muscle Anatomy 101
Part II
Muscle Contraction
Huxley Sliding Filament Theory
Briefly- actin slides over myosin causing the z-lines to pull together; thus shortening the sarcomere
Action potential travels to neuromuscular junction
Acetylcholine (Ach) is released
Sarcolema is depolarized
Muscle fiber is excited
Ca++ is released from sarcoplasmic reticulum
Ca++ binds to troponin
Myosin heads bind to actin
Powerstroke occurs
ATP binds to crossbridge
Myosin detaches from actin
If Ca++ and ATP are present cycle occurs again if physically possible
Muscle Contraction
Relaxation occurs when stimulus stops
Ca++ is actively pumped back into SR
ATP is required for excitation and relaxation
Size Principle
“Motor units are recruited from the smallest to the largest based on the force demands placed on the muscle.”
Smaller (lower threshold) units are recruited first (predominately Type I)
Based on force demands larger (higher threshold) units are recruited (predominately Type II)
Size Principle
*Important Training Concept*
Low resistance = smaller units = 12-15RMHigh resistance = larger units = 1-5RM
*Only recruited units benefit from training*
All-or-None Law
“When a specific motor unit reaches its threshold level for action, all of the muscle fibers in that motor unit are activated fully.”
-Refers to individual unit NOT entire muscle
-Variation of force
Muscle Activation & Training
Different loads recruit different types and numbers of motor units
Heavier loads recruit more units
Exception to size principle: High velocity movements
Muscle Activation & Training
Recruiting low threshold first delays muscular fatigue for submax exercise
Neurons of high threshold units ability to recover quickly allows them to be activated quicker in repeated actions
Muscle Activation & Training
-To achieve training effect of Type II there must be high power output demands
-Recruitment order is generally fixed, may change due to body position-exercising at various angles?
Muscle Actions
Concentric: active shortening (m. force > resistance)
Eccentric: lengthening (m. force<resistance)
Isometric: static (m. force=resistance)
Muscle Actions
Ascending Curve: force gets greater throughout ROM
Descending Curve: force greatest at beginning
Bell Curve: force greatest in middle
Length-Tension (Force) CurveOptimal length at which muscle can generate force Optimal length: maximal crossbridge interaction
Force Velocity Curve
“As the velocity of muscular movement increases, the force a muscle is able to develop concentrically decreases”
-The greater the force the slower the movement (concentrically)
*Opposite true for eccentric muscle actions
Force Velocity Curve
High force development is related to tissue damage-Muscle soreness after eccentric exercise
Questions?