Meeting Abstract
In vertebrate skeletal muscle, increases in the intensity of recruitment has been shown to result in a left-shift of the muscle’s optimal length (Lo). However, it remains unclear how recruitment influences the width of the force-length relationship (the range of muscle and fiber lengths where near-maximal force can be produced) and thus the scope of its performance. We hypothesized that increased recruitment intensity (from twitch to tetanic stimuli) would result in a widening of the active force-length curve, and that this effect would be relatively insensitive to fiber type composition and architecture. We measured twitch and supramaximal tetanic force-length curves for the mouse tibialis anterior (TA), a fast-fibered, relatively pennate muscle, in situ (n=5) and soleus (SOL), a slow-fibered, relatively parallel muscle, in vitro (n=5). Near-optimal length range was measured from 90 – 100% Po on the ascending force-length curve limb. The width of the active force-length curve was significantly (p<0.01) greater for tetanic than twitch stimulation for TA (20.8 ± 18.8%; mean ± S.E.M.) and SOL (43.4 ± 20.0%). This broadening of the range of fiber lengths where a muscle can produce near-optimal force is likely important when cadence and joint range-of-motion is increased to produce faster movement.
