Received December 18, 2006
Revised December 27, 2006
Accepted after revision January 12, 2007

¹ Manchester Metropolitan University

^* To whom correspondence should be addressed. E-mail: a.j.sargeant{at}mmu.ac.uk.

	Abstract

Measurements of human power need to be interpreted in relation to the movement frequency since that will determine the velocity of contraction of the active muscle and hence the power available, according to the power/velocity relationship. Techniques are described which enable movement frequency to be kept constant during human exercise under different conditions. Combined with Micro-dissection and analysis of muscle fibre fragments from needle biopsy obtained pre- and post-exercise, we have been able ‘to take the muscle apart’ having measured the power output, including the effect of fatigue, under constant movement frequency conditions. We have shown that fatigue may be the consequence of a metabolic challenge to a relatively small population of fast fatigue sensitive fibres as indicated by [ATP] depletion to ~30% of resting values in fibres expressing IIX MyHC isoform after just 10 seconds of dynamic exercise. Because these same fibres are predicted to have a high maximal velocity of contraction they also make a disproportionate contribution to power output in relation to their number, especially at faster movement rates. The micro-dissection technique can also be used to measure [PCr] which is an exquisitely sensitive marker of muscle fibre activity- thus in just seven brief contractions [PCr] is depleted to levels < 50% of rest in all muscle fibre types. The technique has been applied to study exercise at different intensities, and to compare recruitment in lengthening shortening and isometric contractions, thus yielding new information on patterns of recruitment, energy turnover, and efficiency.

Key Words: Adenosine triphosphate, Exercise, Myosin

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