MUSCLE IMP ACCUMULATION IN TRAINED AND UNTRAINED MEN DURING SUBMAXIMAL CYCLING TO FATIGUE

Abstract

719 This study was undertaken to compare the accumulation of IMP within the contracting muscle of endurance trained and untrained men following prolonged submaximal exercise to fatigue. Seven endurance trained (28.3 ± 1.7 yrs; 67.7 ± 2.8 kg; VO2max = 65.8 ± 2.4 ml/kg/min, mean± SEM) and six untrained (21.8 ± 1.4 yrs; 79.7 ± 4.4 kg; VO2max = 46.2 ± 1.9 ml/kg/min) men cycled to fatigue at a work rate calculated to require 70% peak oxygen uptake. Time to exhaustion was 36% longer (P < 0.01) in trained compared with untrained men (148 ± 11 and 95 ± 8 min, respectively). Glycogen content was extremely low in both TR and UT (112 ± 38 and 76 ± 35 mmol/kg dw, respectively) at fatigue and no differences for this metabolite were observed between the groups at this point. Despite the low muscle glycogen content at fatigue in TR, inosine 5'-monophosphate (IMP), a marker of metabolic stress, was not different compared with rest. In contrast, significant (P < 0.01) accumulation of IMP was observed at fatigue in UT. Additionally, the exercise-induced change in total adenine nucleotide (TAN = ATP + ADP + AMP) content tended (P = 0.06) to be greater in UT compared with TR. These data demonstrate that fatigue was associated with a similar low level of intramuscular glycogen in both trained and untrained men. Furthermore, fatigue from prolonged exercise in untrained men resulted in a compromised ADP rephosphorylation rate, which may be related to fatigue; whereas in endurance trained men, fatigue is probably related to factors other than impaired ATP resynthesis.