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 O2 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 O2 (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.