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This Article Full Text Full Text (PDF) All Versions of this Article: 92/2/323    most recent expphysiol.2006.034322v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Sargeant, A. J. Search for Related Content PubMed PubMed Citation Articles by Sargeant, A. J. Related Collections Symposia Papers

¹ Institute for Biophysical and Clinical Research into Human Movement, Manchester Metropolitan University, Manchester, UK ² Institute for Fundamental and Clinical Human Movement Science, Vrije University, Amsterdam, The Netherlands

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 microdissection and analysis of muscle fibre fragments from needle biopsies obtained pre- and postexercise we have been able ‘to take the muscle apart’, having measured the power output, including the effect of fatigue, under conditions of constant movement frequency. 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 those fibres expressing myosin heavy chain isoform IIX after just 10 s of maximal dynamic exercise. Since these same fibres will 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 microdissection technique can also be used to measure phosphocreatine concentration ([PCr]), which is an exquisitely sensitive indicator of muscle fibre activity; thus, in just seven brief maximal 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.

(Received 18 December 2006; accepted after revision 12 January 2007; first published online 7 March 2007)
Corresponding author A. J. Sargeant: Institute for Biophysical and Clinical Research into Human Movement, Manchester Metropolitan University, Hassall Road, Alsager, Cheshire ST7 2HL, UK. Email: a.j.sargeant{at}mmu.ac.uk

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