Reduced volume and increased training intensity elevate muscle Na+-K+ pump α2-subunit expression as well as short- and long-term work capacity in humans

Bangsbo J, Gunnarsson TP, Wendell J, Nybo L, Thomassen M. Reduced volume and increased training intensity elevate muscle Na+-K+ pump alpha(2)-subunit expression as well as short-and long-term work capacity in humans. J Appl Physiol 107: 1771-1780, 2009. First published October 1, 2009; doi:10.1152/japplphysiol.00358.2009.-The present study examined muscle adaptations and alterations in work capacity in endurance-trained runners as a result of a reduced amount of training combined with speed endurance training. For a 6- to 9-wk period, 17 runners were assigned to either a speed endurance group with a 25% reduction in the amount of training but including speed endurance training consisting of six to twelve 30-s sprint runs 3-4 times/wk (SET group n = 12) or a control group (n = 5), which continued the endurance training (similar to 55 km/wk). For the SET group, the expression of the muscle Na+-K+ pump alpha(2)-subunit was 68% higher (P < 0.05) and the plasma K+ level was reduced (P < 0.05) during repeated intense running after 9 wk. Performance in a 30-s sprint test and the first of the supramaximal exhaustive runs was improved (P < 0.05) by 7% and 36%, respectively, after the speed endurance training period. In the SET group, maximal O-2 uptake was unaltered, but the 3-km (3,000-m) time was reduced (P < 0.05) from 10.4 +/- 0.1 to 10.1 +/- 0.1 min and the 10-km (10,000-m) time was improved from 37.3 +/- 0.4 to 36.3 +/- 0.4 min (means +/- SE). Muscle protein expression and performance remained unaltered in the control group. The present data suggest that both short-and long-term exercise performances can be improved with a reduction in training volume if speed endurance training is performed and that the Na+-K+ pump plays a role in the control of K+ homeostasis and in the development of fatigue during repeated high-intensity exercise.