Meeting Abstract
LBS1.8 Thursday, Jan. 3 The relationship between EMG and strain rate in muscle fascicles: what should we expect and what do we find? CARROLL, Andrew M.*; RICHARDS, Christopher; Concord Field Station, Harvard University; Concord Field Station, Harvard University acarroll@oeb.harvard.edu
Electromyographic intensity is generally agreed to reflect the area of recruited fascicles, and, thus, increases in EMG (for a given load) are expected to decrease the stress on individual myofibers and increase their velocity of shortening (or decrease their velocity of stretching). As load varies (as with increased locomotor speed or incline), recruitment may over-compensate for load to permit increased strain rates, match increases in load to conserve fascicle strain rate, or under-compensate to reduce strain rate (or increase the rate of stretch). In the first part of this discussion, EMG and strain rate patterns measured from goat forelimb musculature and abstracted from published literature are compared to assess whether muscles with different functional roles (i.e. force production or power production) display differing EMG-strain rate relationships. Increases in the magnitude of EMG intensity, however, are correlated with increased contractile area per fascicle and with increased Vmax of recruited fibers. The second part of this discussion investigates how these correlations might affect the relationship between EMG and fascicle strain rate as recruitment increases in mixed muscle and compares these predictions about the EMG-strain rate relationship with those measured in forelimb muscles of goats and abstracted from published literature measurements for vertebrate mixed muscle. The goal of this comparison is to address whether confounding effects of EMG intensity are detectable in vivo. Finally, the effect of locomotor conditions i.e. in aquatic vs. terrestrial species) on the delay between strain and activation is briefly discussed.
