Effect of training on the activity of five muscle enzymes studied on elite cross-country skiers

This study examines the effect of training intensity on the activity of enzymes in m. vastus lateralis. Elite junior cross-country skiers of both sexes trained 12±15 h weeks±1 for 5 months at either moderate (60±70% of VO2max, MIG) or high training intensity (80±90% of the VO2max, close to the lactate threshold; HIG). Muscle biopsies for enzyme analyses and fibre typing were taken before and after the training period. Histochemical analyses on single fibres were done for three enzymes (succinate dehydrogenase [SDH], hydroxybutyrate dehydrogenase [HBDH], glycerol-3-phosphate dehydrogenase [GPDH]), while the activity of citrate synthase [CS] and phosphofructokinase [PFK] was measured on whole biopsies. The activity of GPDH was low in ST fibres and high in FT fibres.The activity of SDH and HBDH was high in both ST and FTa fibres but low in the FTb fibres. The HIG increased their performance more than the MIG did during the training period as judged from scores on a 20-min run test. The SDH activity rose by 6% for the HIG (P < 0.02). No effects of training were found in the activities of CS, HBDH or GPDH, neither in the two training groups nor for the two genders (P < 0.16). The PFK...