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Opposing effects of acute and chronic high intensity exercise on Na+K+ATPase activity in skeletal muscle

R.J. Aughey1, K.T. Murphy1, S.A. Clark2, J. Christie2, A.G. Hahn3, C.J. Gore3, A.P. Garnham4, C.M. Chow5, J.A. Hawley2 and M.J. McKenna1, 1Centre for Rehabilitation, Exercise and Sports Science, Victoria University of Technology, Melbourne, 2RMIT University, Melbourne, 3Australian Institute of Sport, Canberra, 4Deakin University, Melbourne and 5University of Sydney, NSW, Australia.

The Na+K+ATPase enzyme is critical in maintaining muscle trans-sarcolemmal [Na+] and [K+] gradients and membrane excitability. However, repeated maximal muscle contractions reduce maximal Na+K+ATPase activity (Fraser et al., 2002). High-intensity interval training is commonly used by endurance athletes to improve endurance performance, but the effects of acute high-intensity interval exercise on muscle Na+K+ATPase activity are not known. Furthermore, although sprint training increases muscle Na+K+ATPase content (McKenna et al., 1993), the effects of high-intensity interval training on muscle Na+K+ATPase activity are unknown. We therefore examined the possible contradictory effects of acute and chronic high-intensity interval exercise on the muscle Na+K+ATPase activity in seven male endurance-trained athletes.

A vastus lateralis muscle biopsy was taken at rest, 3-wks prior to (Base), at rest and immediately after exercise prior to (Pre) and after (Post) 3-wks of training. Muscle samples were analysed for maximal in vitro Na+K+ATPase (K+ stimulated 3-O-MFPase) activity. Performance was characterised by incremental V-dotO2 and peak power output (PPO); and during a simulated 40km time-trial, by mean power output (MPO). A t-test was used for resting 3-O-MFPase activity to determine reproducibility (Base – Pre) and to compare change scores (Base–Pre, & Pre-Post) to identify a change with training. A two-way ANOVA with repeated measures was applied to test for main effects of exercise (Rest, Ex) and training (Pre, Post).


Resting muscle 3-O-MFPase activity did not differ between Base and Pre. Acute high-intensity interval exercise depressed muscle 3-O-MFPase activity by 12.7±1.2% (mean±SEM, Exercise main effect, P<0.05, *, see figure). In contrast, training increased 3-O-MFPase activity by 4.9±0.7% (training main effect, p<0.05, , see figure). Resting 3-O-MFPase activity was increased after training by 5.4±1.0% (Pre – Post change score, P<0.05). Neither V-dotO2 (Base 64.4±1.6; Pre 64.3±1.5; Post 65.8±1.9), PPO (Base 368±12; Pre 374±13; Post 379±14), or MPO in the 40km time-trial (Base 279±12; Pre 303±15; Post 303±13) differed significantly after training.

In conclusion, Na+K+ATPase measures were reproducible in resting muscle. Acute and chronic high-intensity interval exercise had converse effects on Na+K+ATPase activity. The small rise in Na+K+ATPase activity with training was insufficient to improve exercise performance.

Fraser, S. F., Li, J. L., Carey, M. F., Wang, X. N., Sangkabutra, T., Sostaric, S., Selig, S.E., Kjeldsen, K. & McKenna, M. J. (2002) Journal of Applied Physiology, 93, 1650-1659.

McKenna, M.J., Schmidt, T.A., Hargreaves, M., Cameron, L., Skinner, S.L. & Kjeldsen, K. (1993) Journal of Applied Physiology, 75, 173-180.

This study was partially funded by an Australian Research Council SPIRT grant (C00002552).