Human Muscle Power

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The ability of generating muscle power power is important whether you are an Olympic athlete, a ballet dancer, or an elderly person wanting to climb the stairs to go to bed. In this comprehensive review of his research Anthony Sargeant points out the importance of different types of muscle fibres that make up the human skeletal muscles that produce power in legs and arms. Tony also points out that in research seeking to measure human muscle power it is essential to measure or control the speed at which the power is generated (this is because power is the product of work and velocity).

Structural and functional determinants of human muscle power
by Anthony J Sargeant

Experimental Physiology
Exp Physiol. 2007 Mar;92(2):323-31

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 approximately 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.

Anthony J Sargeant

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