Effect of 2-wk intensified training and inactivity on muscle Na+-K+ pump expression, phospholemman (FXYD1) phosphorylation, and performance in soccer players

Thomassen M, Christensen PM, Gunnarsson TP, Nybo L, Bangsbo J. Effect of 2-wk intensified training and inactivity on muscle Na+-K+ pump expression, phospholemman (FXYD1) phosphorylation, and performance in soccer players. J Appl Physiol 108: 898-905, 2010. First published February 4, 2010; doi:10.1152/japplphysiol. 01015.2009.-The present study examined muscle adaptations and alterations in performance of highly trained soccer players with intensified training or training cessation. Eighteen elite soccer players were, for a 2-wk period, assigned to either a group that performed high-intensity training with a reduction in the amount of training (HI, n = 7), or an inactivity group without training (IN, n = 11). HI improved (P < 0.05) performance of the 4th, 6th, and 10th sprint in a repeated 20-m sprint test, and IN reduced (P < 0.05) performance in the 5th to the 10th sprints after the 2-wk intervention period. In addition, the Yo-Yo intermittent recovery level 2 test performance of IN was lowered from 845 +/- 48 to 654 +/- 30 m. In HI, the protein expression of the Na+-K+ pump alpha(2)-isoform was 15% higher (P < 0.05) after the intervention period, whereas no changes were observed in alpha(1)- and beta(1)-isoform expression. In IN, Na+-K+ pump expression was not changed. In HI, the FXYD1ser68-to-FXYD1 ratio was 27% higher (P < 0.01) after the intervention period, and, in IN, the AB_FXYD1ser68 signal was 18% lower (P < 0.05) after inactivity. The change in FXYD1ser68-to-FXYD1 ratio was correlated (r(2) = 0.35; P < 0.05) with change in performance in repeated sprint test. The present data suggest that short-term intensified training, even for trained soccer players, can increase muscle Na+-K+ pump alpha(2)-isoform expression, and that cessation of training for 2 wk does not affect the expression of Na+-K+ pump isoforms. Resting phosphorylation status of the Na+-K+ pump is changed by training and inactivity and may play a role in performance during repeated, intense exercise.