Separate and combined effects of known fatigue parameters on power during cyclic contractions

Muscular power is reduced with fatigue [1,3]. During cyclic contractions muscular power is highly dependent upon force-velocity characteristics (F0, Vmax, curvature) and activation-deactivation dynamics [2], which change with fatigue [1,3]. Determining the contribution of changes to each characteristic to the net loss of power in a living muscle is challenging. Therefore, we used modelling to determine the influence of these changes, individually and in combination, to muscular power during cyclic contractions. Our results show that fatigue of maximal isometric force decreased positive power and was the primary contributor to net power lost at lower frequencies. Increased relaxation time increased negative power during lengthening, particularly at higher frequencies. Thus, the relative importance of changes to these two contractile characteristics depended on movement frequency. Changes to other factors (Vmax, curvature) had minimal effect.