Fatigue in 10 second sprints and human muscle fibre type

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This research was carried out by the talented Christina Karatzaferi as part of her PhD under the direction of Tony Sargeant. Utilizing techniques developed in his laboratory fragments of human muscle fibres were micro-dissected from samples obtained using the needle biopsy technique immediately after a 10 second sprint. Separated fragments were then classified according to fibre type. The level of high energy phosphate was measured in each fibre type and compared to the levels before exercise. This study is part of a long series concerned with anaerobic power and fatigue in human muscle starting with the paper published in 1981 (Sargeant, Hoinville and Young 1981 – note: although not written up until 1981 the work for this paper was actually conducted in the mid 1970s when Tony was working for the Medical Research Council).
Experimental Physiology
Exp Physiol. 2001 May;86(3):411-5

Abstract:

Changes in high-energy phosphate levels in single human skeletal muscle fibres after 10 s of maximal (all-out) dynamic exercise were investigated. Muscle biopsies from vastus lateralis of two volunteers were collected at rest and immediately post exercise. Single muscle fibres were dissected from dry muscle and were assigned into one of four groups according to their myosin heavy chain (MyHC) isoform content: that is type I, IIA, IIAx and IIXa (the latter two groups containing either less or more than 50% IIX MyHC).

Fragments of characterised fibres were analysed by HPLC for ATP, inosine-monophosphate (IMP), phosphocreatine (PCr) and creatine levels. After 10 s of exercise, PCr content ([PCr]) declined by approximately 46, 53, 62 and 59 % in type I, IIA, IIAx and IIXa fibres, respectively (P < 0.01 from rest). [ATP] declined only in type II fibres, especially in IIAx and IIXa fibres in which [IMP] reached mean values of 16 +/- 1 and 18 +/- 4 mmol (kg dry mass)(-1), respectively. While [PCr] was reduced in all fibre types during the brief maximal dynamic exercise, it was apparent that type II fibres expressing the IIX myosin heavy chain isoform were under a greatest metabolic stress as indicated by the reductions in [ATP].

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