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

Skinned fibres have advantages for comparing the muscle properties of different animal species because they can be prepared from a needle biopsy taken under field conditions. However, it is not clear how well the contractile properties of skinned fibres reflect the properties of the muscle fibres in vivo. Here, we compare the mechanical performance of intact fibre bundles and skinned fibres from muscle of the same animals. This is the first such direct comparison. Maximum power and isometric force were measured at 25 degrees C using peroneus longus (PL) and extensor digiti-V (ED-V) muscles from wild rabbits (Oryctolagus cuniculus). More than 90% of the fibres in these muscles are fast-twitch, type 2 fibres. Maximum power was measured in force-clamp experiments. We show that maximum power per volume was the same in intact (121.3 +/- 16.1 W l(-1), mean +/- s.e.m.; N=16) and skinned (122.6 +/- 4.6 W l(-1); N=141) fibres. Maximum relative power (power/F-IM L-o, where F-IM is maximum isometric force and Lo is standard fibre length) was also similar in intact (0.645 +/- 0.037; N=16) and skinned (0.589 +/- 0.019; N=141) fibres. Relative power is independent of volume and thus not subject to errors in measurement of volume. Finally, maximum isometric force per cross-sectional area was also found to be the same for intact and skinned fibres (181.9 kPa +/- 19.1; N=16; 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.