Acute changes in muscle activation and leg extension performance after different running exercises in elite long distance runners

This study investigated acute changes in muscle activation and muscular power performance after three different running exercises in elite long-distance runners. Twenty-two nationally and internationally ranked long-distance runners performed first an incremental treadmill running test until exhaustion (MR) and then 40 min continuous (TR) and intermittent (2 min run/2 min rest) (IR) running exercises at an intensity of 80 and 100% of the velocity associated with VO_2max, respectively. Muscle activation and muscular power performance tests (counter-movement jumps, CMJ, and a set of ten maximal half squats from the static starting position with an extra load of 35% of the subjects,´ one repetition maximum) were performed before and immediately after the runs. The average mechanical power (P) of the half squats was calculated and the root mean square electromyogram (EMGrms) from the vastus lateralis, vastus medialis, gastrocnemius and biceps femoris muscles was recorded simultaneously during the half squat performances. The results showed an acute exercise–induced increase in P (ANOVA time effect, P=0.000) together with a reduction in EMGrms of the knee extensor muscles (ANOVA time effect, P=0.000). However, mechanical P expressed as a relative change within the set decreased after MR. In TR the improvement in P correlated positively with the maximal running performance of the runners (P<0.05), while in IR it correlated negatively (P<0.05). Jumping performance was significantly enhanced after each run (P<0.001, for all) and the improvement correlated negatively with the maximal sprinting speed and maximal jumping height of the runners (P<0.01, for all). It is concluded that in elite long distance runners an intensive prolonged running exercise reduces the surface EMG of the knee extensor muscles, and may lead to a different coordination strategy in leg extension exercises performed into the vertical direction. After continuous type of running the power improvement correlates positively with maximal endurance running capacity, whereas after intermittent type of running it correlates negatively.