MODELING RED MUSCLE POWER OUTPUT DURING STEADY AND UNSTEADY SWIMMING IN LARGEMOUTH BASS

We recorded electromyograms of slow-twitch (red) muscle fibers and vid eotaped swimming in the largemouth bass (Micropterus salmoides) during cruise, burst-and-glide, and C-start maneuvers. By use of in vivo pat terns of stimulation and estimates of strain, in vitro power output wa s measured at 20 degrees C with the oscillatory work loop technique on slow-twitch fiber bundles from the midbody area near the soft dorsal fin. Power output increased slightly with cycle frequency to a plateau of similar to 10 W/kg at 3-5 Hz, encompassing the normal range of tai l-beat frequencies for steady swimming (similar to 2-4 Hz). Power outp ut declined at cycle frequencies simulating unsteady swimming (burst-a nd-glide, 10 Hz; C-start, 15 Hz). However, activating the muscle at 10 Hz did significantly increase the net work done compared with the wor k produced by the inactive muscle (work done by the viscous and elasti c components). Thus this study provides further insight into the appar ently paradoxical observation that red muscle can contribute little or no power and yet continues to show some recruitment during unsteady s wimming. Comparison with published values of power requirements from o xygen consumption measurements indicates a limit to steady swimming sp eed imposed by the maximum power available from red muscle.