Abstract Aim: To investigate if exercise intensity and Ca(2+) signalling regulate Na(+), K(+) pump mRNA expression in skeletal muscle. Methods: The importance of exercise intensity was evaluated by having trained and untrained humans perform intense intermittent and prolonged exercise. The importance of Ca(2+) signalling was investigated by electrical stimulation of rat soleus and EDL muscles in combination with studies of cell cultures. Results: Intermittent cycling exercise at approximately 85% of VO(2peak) increased (P<0.05) alpha1 and beta1 mRNA expression approximately 2 fold in untrained and trained subjects. In trained subjects, intermittent exercise at approximately 70% of VO(2peak) resulted in a less (P<0.05) pronounced increase ( approximately 1.4 fold; P<0.05) for alpha1 and no change in beta1 mRNA. Prolonged low intensity exercise increased (P<0.05) mRNA expression of alpha1 approximately 3.0 fold and alpha2 approximately 1.8 fold in untrained but not in trained subjects. Electrical stimulation of rat soleus, but not EDL, muscle increased (P<0.05) alpha1 mRNA expression, but not when combined with KN62 and cyclosporine A incubation. Ionomycin incubation of cultured primary rat skeletal muscles increased (P<0.05) alpha1 and reduced (P<0.001) alpha2 mRNA expression and these responses were abolished (P<0.05) by co-incubation with cyclosporine A or KN62. Conclusion: 1) Exercise induced increases in Na(+), K(+) pump alpha1 and beta1 mRNA expression in trained subjects are more pronounced after high- than after moderate- and low-intensity exercise 2) Both prolonged low and short-duration high intensity exercise increase alpha1 mRNA expression in untrained subjects 3) Ca(2+) (i) regulates alpha1 mRNA expression in oxidative muscles via CaMK and calcineurin signalling pathways.