Intensive training and reduced volume increases muscle FXYD1 expression and phosphorylation at rest and during exercise in athletes

The present study examined the effect of intensive training in combination with marked reduction in training volume on FXYD1 expression and phosphorylation at rest and during exercise. Eight well-trained cyclist replaced their regular training with speed-endurance training (10-12 x ~30-s sprints) 2-3 times per week and aerobic high-intensity training (4-5 x 3-4 min at 90-95% of peak aerobic power output) 1-2 times per week for seven weeks and reduced the training volume by 70%. Muscle biopsies were obtained before and during a repeated high-intensity exercise protocol and protein expression and phosphorylation were determined by western blotting. Expression of FXYD1 (30%), actin (40%), mTOR (12%), PLN (16%) and CaMKII γ/δ (25%) was higher (P<0.05) after compared to before the training intervention. In addition, after the intervention non-specific FXYD1 phosphorylation was higher (P<0.05) at rest and during exercise, mainly achieved by an increased FXYD1 ser68 phosphorylation, compared to before the intervention. CaMKII thr287 and eEF2 thr56 phosphorylation at rest and during exercise, overall PKCα/β thr638/641 and mTOR ser2448 phosphorylation during repeated intense exercise as well as resting PLN thr17 phosphorylation were also higher (P<0.05) after compared to before the intervention period. Thus, a period of high intensity training with reduced training volume increases expression and phosphorylation levels of FXYD1, which may affect Na(+)/K(+) pump activity and muscle K+ homeostasis during intense exercise. Furthermore, higher expression of CaMKII and PLN as well as increased phosphorylation of CaMKII thr287 may have improved intracellular Ca2+ handling.