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 (HR_max) to 2.7 h week^‐1 and a mean intensity of 78% of HR_max. 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 Vo_2max from 54.9 + 3.1 to 58.3±3.0 ml 0₂ min^‐1 kg^‐1 (P < 0.0001). Exercise time to exhaustion at 86% of Fo_2max (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 ' (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.