Effects of intensified endurance training on the concentration of Na,K-ATPase and Ca-ATPase in human skeletal muscle.

Thirty-nine moderately endurance trained males increased their normal training programme of 2.2 h week-1 with an average training intensity of 65% of maximum heart rate (HRmax) to 2.7 h week-1 and a mean intensity of 78% of HRmax. Performance tests and measurements of the total concentrations of Na,K-ATPase (3H-ouabain binding) and Ca-ATPase, fibre type distribution and fibre area were performed in biopsies from the vastus lateralis muscle before and after increased training. The 6 weeks of training elevated VO2max from 54.9 +/- 3.1 to 58.3 +/- 3.0 ml O2 min-1 kg-1 (P < 0.0001). Exercise time to exhaustion at 86% of VO2max (pre-training) increased from 35 +/- 8 to 61 +/- 17 min (P < 0.0001). The concentration of Ca-ATPase was unaffected by the intensified training (6.74 +/- 1.03 vs. 6.68 +/- 1.07 nmol g wet wt-1), but the concentration of Na,K-ATPase increased from 307 +/- 43 to 354 +/- 59 pmol g wet wt-1 (P < 0.0001). The relative distribution of FT-fibres was correlated with the concentration of Ca-ATPase (r = 0.72, P < 0.0001). The data support the view that intensive training induces an upregulation of the concentration of skeletal muscle Na,K-ATPase, but no change in the total capacity for reaccumulation of Ca2+ into the SR. There was no correlation between the concentrations of Na,K-ATPase, Ca-ATPase and indices of endurance performance.