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ENVIRONMENTAL, EXERCISE AND RESPIRATORY PHYSIOLOGY

Reduced volume but increased training intensity elevates muscle Na⁺-K⁺ pump ₁-subunit and NHE1 expression as well as short-term work capacity in humans

¹Department of Exercise and Sport Sciences, Section of Human Physiology, Copenhagen Muscle Research Center, University of Copenhagen, Copenhagen, Denmark; and ²Faculty of Exercise Sciences, State University of Milan, Milan, Italy

Submitted 14 September 2007 ; accepted in final form 11 December 2007

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 (45 km/wk). After the 4-wk sprint period, the expression of the muscle Na⁺-K⁺ pump ₁-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.

fatigue; pH; lactate; performance; sodium-potassium-chloride 1 protein cotransporters

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