Reduced volume but increased training intensity elevates muscle Na+-K+ pump alpha1-subunit and NHE1 expression as well as short-term work capacity in humans

F Marcello Iaia, Martin Thomassen, Helle Kolding, Thomas Gunnarsson, Jesper Wendell, Thomas Rostgaard, Nikolai Nordsborg, Peter Krustrup, Lars Nybo, Ylva Hellsten, Jens Bangsbo
American Journal of Physiology. Regulatory, Integrative and Comparative Physiology 2008, 294 (3): R966-74
The present study examined muscle adaptations and alterations in work capacity in endurance-trained runners after a change from endurance to sprint training. Fifteen runners were assigned to either a sprint training (ST, n = 8) or a control (CON, n = 7) group. ST replaced their normal training by 30-s sprint runs three to four times a week, whereas CON continued the endurance training (approximately 45 km/wk). After the 4-wk sprint period, the expression of the muscle Na+-K+ pump alpha1-subunit and Na+/H+-exchanger isoform 1 was 29 and 30% higher (P < 0.05), respectively. Furthermore, plasma K+ concentration was reduced (P < 0.05) during repeated intense running. In ST, performance in a 30-s sprint test, Yo-Yo intermittent recovery test, and two supramaximal exhaustive runs was improved (P < 0.05) by 7, 19, 27, and 19%, respectively, after the sprint training period, whereas pulmonary maximum oxygen uptake and 10-k time were unchanged. No changes in CON were observed. The present data suggest a role of the Na+-K+ pump in the control of K+ homeostasis and in the development of fatigue during repeated high-intensity exercise. Furthermore, performance during intense exercise can be improved and endurance performance maintained even with a reduction in training volume if the intensity of training is very high.

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