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 (∼55 km/wk). For the SET group, the expression of the muscle Na+-K+pump α2-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 O2uptake 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.
The Effect of Short and Long Term Endurance Training on Systemic, and Muscle and Prefrontal Cortex Tissue Oxygen Utilisation in 40 – 60 Year Old Women
