Metabolic changes in single human muscle fibres during brief maximal exercise

Changes in high-energy phosphate levels in single human skeletal muscle fib res after 10 s of maximal (all-out) dynamic exercise were investigated. Mus cle biopsies from vastus lateralis of two volunteers were collected at rest and immediately post exercise. Single muscle fibres were dissected from dr y muscle and were assigned into one of four groups according to their myosi n heavy chain (MyHC) isoform content: that is type I, IIA, IIAx and Wa (the latter two groups containing either less or more than 50% IIX MyHC). Fragm ents of characterised fibres were analysed by HPLC for ATP, inosine-monopho sphate (IMP), phosphocreatine (PCr) and creatine levels. After 10 s of exer cise, PCr content ([PCr]) declined by approximately 46, 53, 62 and 59% in t ype I, IIA, IIAx and IIXa fibres, respectively (P < 0.01 from rest). [ATP] declined only in type II fibres, especially in IIAx and Wa fibres in which [IMP] reached mean values of 16<plus/minus>1 and 18 +/-4 mmol (kg dry mass) (-1), respectively. While [PCr] was reduced in all fibre types during the b rief maximal dynamic exercise, it was apparent that type II fibres expressi ng the IIX myosin heavy chain isoform were under a greatest metabolic stres s as indicated by the reductions in [ATP].