During a single lower limb extensor movement over a fixed distance, the power-velocity relationship obtained against an inertial load, provided by an adjustable flywheel is parabolic (Pearson et al. 2000). The reason for the decline in the peak power that can be obtained at high inertias may result from the completion of the movement before the load can be accelerated to an optimal velocity for peak power generation. In contrast to a single movement, a repeated action performed against a high inertial load, such as cycling, should allow for the progressive acceleration of an inertial load. It was thus hypothesised that the peak power output measured during sprint cycling would, within limits, be independent of the level of inertia, but would depend upon the time allowed for the acceleration of the load.

In the present study approved by the local ethics committee, we examined the power generated by the lower limb muscles of nine healthy men; mean age (29.4 ± 2.2 years) using two different test protocols. Following a 5-min warm up, the subjects performed a single maximal lower limb thrust (T1), on a variable inertial flywheel system (Pearson et al. 2000). Each subject performed two exertions at five inertial loads in a randomised order ranging from 0.024 to 0.54 kg m². In T2, performed on a separate occasion, two sprints were performed at each of the same inertias on a modified cycle ergometer attached to the flywheel assembly. The best exertion at each inertia was used for purposes of analysis.

In T1 the maximal values for peak power occurred at an inertia of 0.158 kg m² and declined thereafter. In T2 there was no significant change in peak power beyond 0.158 kg m². The time to reach peak power was 0.99 ± 0.10 s (~1.4 crank revs) and 2.39 ± 0.14 s (~2.8 crank revs) at 0.158 and 0.54 kg m², respectively (P < 0.05). It is likely that a similar value of peak power will always be achieved during cycling against different inertial loads. This is because as an inertial load accelerates, a muscle will move down its force-velocity relationship and eventually achieve a velocity that corresponds to its optimum for power generation (~30 % V_max). This is providing that (i) the muscle is not fatigued at this point and (ii) the inertia is of sufficient magnitude to allow forces to be produced that are initially greater, or equal, to those at which peak power can be generated.

S.D.R.H. is a Wellcome Trust research fellow.