Meeting Abstract
74.4 Tuesday, Jan. 6 Maximizing power and efficiency from a limb during cyclic contractions WAKELING, James M*; BLAKE, Ollie; Simon Fraser University; Simon Fraser University wakeling@sfu.ca
Maximizing the power output from a muscle, from the single fibre to the whole belly level, involves: (a) maximizing the level of activation (mainly during the concentric phase) with zero activation elsewhere and (b) allowing the sarcomeres to shorten at their optimal strain rate as predicted by the Hill relation. But how is the power output from a whole limb maximized? In a multisegmental limb there are many muscles and only a fraction of these are considered primary power producers. Muscles additionally function to control joint stiffness, transfer power between joints and move the limb between power producing stages. High power production requires the coordinated action and distributed function of all the muscles in a limb. Indeed, it was hypothesized that power output would be limited by the muscle coordination. Muscle activity (EMG) was measured from ten muscles in the leg while subjects cycled on a stationary dynamometer at the highest effort they could sustain for hour. Every minute the load and target velocity (pedal cadence) were altered and this varied the power output that could be achieved. The mechanical power output was recorded for every pedal cycle. The total EMG intensity across all muscles was calculated as a proxy of metabolic activity. The EMG intensities for all muscles were grouped together for each pedal cycle to form a pattern of coordination, and these patterns were decomposed using principal component analysis. Submaximal power outputs could be achieved with a range of coordination patterns and these occurred with a range of total EMG intensities. Maximum power outputs were achieved with a more limited set of coordination patterns and these corresponded to the more efficient patterns during submaximal power cycling. The maximum power from a limb thus requires specific coordination between all its muscles.
