Hard training for 5 mo increases Na+-K+ pump concentration in skeletal muscle of cross-country skiers

The levels of Na+-K+ pump in the knees extensor muscles of elite junior cross country skiers were analyzed after five months of hard endurance training. Analysis of vastus lateralis muscle samples from elite athletes after prolonged endurance training indicated the presence of elevated levels of Na+-K+ pump which was correlated with the maximal O2 uptake of the male and female subjects. Furthermore, Na+-K+ pump concentration was correlated with running performance and high performance endurance exercise.