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

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 which 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 fourth, sixth and tenth sprint in a repeated 20-m sprint test (RST) and IN reduced (P<0.05) performance in the fifth to the tenth sprint after the 2-wk intervention period. In addition, the Yo-Yo IR2 test performance of IN was lowered from 845+/-48 to 654+/-30 m. In HI the protein expression of the Na(+)/K(+) pump alpha2 isoform was 15% higher (P<0.05) after the intervention period, whereas no changes were observed in alpha1 and beta1 isoform expression. In IN, Na(+)/K(+) pump expression was not changed. In HI, the FXYD1ser68/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/FXYD1 ratio was correlated (r(2)=0.35; P<0.05) with change in performance in RST. The present data suggest that short-term intensified training even for trained soccer players can increase muscle Na(+)/K(+) pump alpha2 isoform expression and that cessation of training for two weeks 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 for performance during repeated intense exercise. Key words: Fatigue, Training cessation, Performance, MCT1.