Variation in the determinants of power of chemically skinned human muscle fibres

Abstract

We have explored the extent to which the maximal velocity of unloaded shortening (V max ), the force generated per unit cross-sectional area (P 0 ) and the curvature of the forcevelocity relationship (a/P 0 in the Hill equation) contribute to differences in peak power of chemically skinned single fibres from the quadriceps muscle of healthy young male subjects. The analysis was restricted to type I and IIA fibres that contained a single type of myosin heavy chain on electrophoretic separation. Force-velocity relationships were determined from isotonic contractions of maximally activated fibres at 15• C. Mean (± s.d.) peak powers were 1.99 ± 0.72 watts per litre (W L −1 ) for type I fibres and 6.92 ± 2.41 W L −1 , for type IIA fibres. The most notable feature, however, was the very large, sevenfold, range of power outputs within a single fibre type. This wide range was a consequence of variations in each of the three components determining power: P 0 , V max and a/P 0 . Within a single fibre type, P 0 varied threefold, and V max and a/P 0 two-to threefold. There were no obvious relationships between P 0 and V max or between P 0 and a/P 0 . However, there was a suggestion of an inverse relationship between a/P 0 and V max , the effect being to reduce, somewhat, the impact of differences in V max on peak power. In searching for the causes of variation in peak power of fibres of the same type, it appears likely that there are two factors, one that affects P 0 and another that leads to variation in both V max and a/P 0 .

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

“…We examined the dependence of force on CSA in our skinned fibres to see whether force per CSA is greater for small than large fibres, as has been reported for skinned fibres from humans (Gilliver et al, 2009). Fig.…”

“…Since there is evidence that force per cross-sectional area (CSA) is greater for small than large fibres in human skinned fibres (Gilliver et al, 2009) and because we are aiming to compare the performance of skinned and intact fibres, we examined the dependence of force on CSA in both intact fibre bundles and skinned fibres (see below). Fig.…”

Lion (Panthera leo) and caracal (Caracal caracal) type IIx single muscle fibre force and power exceed that of trained humans

“…Thus, this would equate to a threefold higher power output for the felids, suggesting that the specific force produced by the fibres contributed more than shortening velocity (V max ). Additionally, the felid type IIx fibres had higher a/P o values compared with humans, which would suggest that these fibres could sustain a greater force at a particular velocity and, thus, produce more power (Woledge et al, 1985;Gilliver et al, 2009).…”

“…33% of maximum force) was completed, the fibre was subjected to a 2ms shortening to 50% of its original fibre length, after which it was immediately re-stretched within 1ms to its original length whilst in activating solution. This method of re-stretching the fibre whilst it is still submerged in activating solution aids in preserving the fibre and sarcomere integrity when subjected to the next series of contractions and re-stretches (Brenner, 1983;Gilliver et al, 2009). The researcher ensured that the force returned to maximum, whereafter the second series containing three different preprogrammed force clamp loads was initiated.…”

“…The protocols explained below were based on those reported previously (Malisoux et al, 2006;Ottenheijm et al, 2011;Gilliver et al, 2009;Bottinelli et al, 1999). Muscle samples were rapidly thawed at 35°C in saline (pH7.4) for not longer than 1min.…”