Skinned fibres produce the same power and force as intact fibre bundles from muscle of wild rabbits

Abstract

We have compared the mechanical performance of intact fibre bundles and skinned fibres from muscle of the same animals. This is the first such direct comparison. The maximum power and isometric force were measured at 25°C using the peroneus longus (PL) and extensor digiti-V (ED-V) muscles from wild rabbits (Oryctolagus cuniculus, Linnaeus). More than 90% of the fibres in these muscles are fast-twitch, type 2 fibres. Maximum power was measured in force-clamp experiments. We found that within the experimental error, intact and skinned fibres produced the same maximum power per volume, 121.3 W litre−1 ±16.1 (s.e.m.), N=16, and 122.6 W litre−1 ±4.6, N=141, respectively, and the same maximum relative power (power/FIM Lo, where FIM is maximum isometric force and Lo is standard fibre length), 0.645±0.037, N=16, and 0.589±0.019, N=141. Relative power is independent of volume and thus not subject to errors in measurement of volume. Maximum isometric force per cross-sectional area was also the same for intact and skinned fibres, 181.9 kPa ±19.1 N=16 and 207.8 kPa ±4.8, N=141, respectively. These results contrast with previous measurements of performance at lower temperatures where skinned fibres produce much less power than intact fibres from both mammals and non-mammalian species.