It is investigated if exercise induced mRNA changes cause similar protein expression changes of Na(+), K(+) pump isoforms (a1, a2, ß1, ß2), FXYD1 and NHE1 in rat skeletal muscle. Expression was evaluated (n=8 per group) in Soleus and EDL after 1 day, 3 days and 3 weeks (5 sessions per week) of either sprint (4 x 3 min sprint + 1 min rest) or endurance (20 min) running. Two hours after exercise on day 1, no change in protein expression was apparent in either training group or muscle, whereas sprint exercise increased the mRNA of Soleus a2 (4.9±0.8 fold; P