Christina Karatzaferi was a talented and very hard working Greek PhD student working in Amsterdam under the supervision of Professor Anthony J Sargeant. The meticulous and time consuming work that she carried out was part of a research programme into human muscle fatigue pursued by Tony Sargeant over many years.
The results show how human muscle fatigue in very short sprint exercise (10 second) is associated with the reduction of high energy phosphate in a small number of fibres in the exercising muscle. Thus the loss of power (that is fatigue) is not attributable to a failure of the whole muscle in the sprint but of a relatively small number of fatigue sensitive fibres.
Exp Physiol. 2001 May;86(3):411-5
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].