Changes in maximal aerobic power, aerobic capacity, and muscle enzyme activities at two stages of the annual training cycle in ski-runners

Summary

Changes of cardiorespiratory capacity, of the activity of seven enzymes involved in energy metabolism and of laboratory endurance were investigated in a group of nine male ski-runners before and after exhausting training and a competing period during the winter.

Despite the decrease in laboratory endurance and total work oxygen consumption between the investigations, $\dot V$O₂ max, O₂-pulse max and O₂ debt did not change; and O₂-pulse per kg b.w. showed a significant increase.

In biopsy samples of the vastus lateralis muscle, the activity of enzymes of carbohydrate metabolism, both anaerobic and total (triose phosphate dehydrogenase — TPDH, lactate dehydrogenase — LDH, hexokinase — HK), and of total aerobic metabolism (citrate synthetase — CS, malate dehydrogenase — MDH), was decreased during this period by 27 to 59% (mean values for different enzymes). The mean activity of cytoplasmic glycerol phosphate dehydrogenase (GPDH) and of hydroxyacyl — CoA dehydrogenase (HOADH) did not change, although the activity of the latter enzyme was decreased in the muscle of those ski-runners who were trained predominantly for speed, and it was increased in those trained mainly for endurance.

The changes in activity of the muscle enzymes associated with glycolysis (TPDH and LDH) and of MDH, connected with metabolism and hydrogen transport between cytoplasmic and aerobic mitochondrial compartments, correlate inversely with those of aerobic capacity (total work O₂ consumption).