Mechanics of Skeletal Muscle Contraction

Force exerted by muscle

Force exerted on muscle

-oppose eachother -goal of muscle contraction = exert tension against load

T = L Load is static (not moving) -overall length of muscle does not change -tension on y axis, time on x axis -axon stimulates muscle with AP -delay = latent period (ECC) -visually defined contraction -relaxation -contraction duration = contraction phase + relaxation period

T > L Load moving under constant tension -moveable load attached to muscle -distance shorted on y axis, time on x axis -shortening of muscle to lift load -latent period is longer

T < L Load moving against muscle contraction Contracting muscle lengthening due to load -lengthening contraction -muscle is contracting, but overall muscle is lengthening ex. to posture against gravity at balance point

Response of single muscle finger to single AP

Total contraction = contraction phase Relaxation

-Distance of shortening on y axis -Requires inital isometric phase during which tension is generated to match load before it moves -ECC + isometric phase = latent period -Shortening occurs in isotonic phase (T >L) -Relaxation

-Sum total of all elastic (non-contractile) elements within muscle fiber =All elastic, everything but contracticle (thick and thin)

Isometric < isotonic -Isotonic includes initial isometric phase. -tension development precedes shortening of muscle, and this isometric phase is included in latent period of isotonic twitch

-duration of shortening during isotonic twitch < duration of tension development during isometric twitch -both contractions show same extend and duration of intracellular Ca rise, but first part of this Ca window in isotonic twitch is taken up by isometric phase, leaving only a portion of the Ca window for the isotonic phase

1. Load-Velocity 2. Frequency-Tension 3. Length-Tension

Inc wt of load Dec shortening distance Dec rate of shortening *Law of Conservation of Energy *E = F * D

Inc # stimulus/AP Inc magnitude as long as they don't encroach on refractory period