One part is used to characterize the fibre type in respect of the heavy chain myosin isoform expressed. The other part of the fragment is analysed for high energy phosphate concentrations. Fibres are classified on the basis of expressing either type I, type IIA, or type IIX myosin heavy chain isoforms. It should be noted however that in the type II population many fibres co-express both IIA and the IIX isoforms and we therefore characterize these fibres on the basis of the degree of co-expression. We have used this technique to examine the time course of high energy phosphate concentration and fatigue in different fibre populations during exercise. The progressive reduction of power during maximal sprint efforts may be interpreted as the cumulative effect of metabolic depletion in successive fibre type populations from IIX to IIXa to IIAx to IIA to I. One important application of the micro-dissection technique is that PCr content may also be used as a very sensitive metabolic marker for fibre type recruitment during very short duration concentric, isometric and eccentric exercise
This review paper is based on an invited key-note lecture given by Professor Anthony J Sargeant to the Polish Physiological Society. As a review it deals with one aspect of the research interests and developments initiated by Professor Sargeant over many years.
Human muscle fatigue: the significance of muscle fibre type variability studied using a micro-dissection approach
Journal of Physiology and Pharmacology 2006 Nov;57 Suppl 10:5-16