Changes in running economy following a repeated bout of downhill running

Abstract

This study investigated whether a repeated bout of downhill running would result in less damage, and thus blunted changes in physiological and biomechanical running economy (RE) parameters, compared with changes induced by the first bout. Twelve male students performed two 30-minute bouts of downhill (-15%) running (DHR1, DHR2) at 70% of maximal aerobic capacity (V̇O 2max), separated by 5 days. Maximal isometric strength of the knee extensors (MVC), muscle soreness (SOR), and plasma myoglobin (Mb) concentration were measured before, and at 0.5, 24, 48, 72, 96 and 120 hours after both DHR1 and DHR2. All subjects performed a 5-minute bout of level running at 85% of V̇O2max before, immediately after, and at 24, 48, 72, 96 and 120 hours after DHR1 and DHR2, during which oxygen consumption (V̇O 2), minute ventilation (V̇E), blood lactate (LA), heart rate (HR), respiratory exchange ratio (RER), and rating of perceived exertion (RPE) were measured. Stride length (SL), stride frequency (SF), and range of motion for the ankle (ROM-A) and knee (ROM-K) during the level runs were analyzed using high-speed (120Hz) video images. The results of this study showed that MVC decreased (p<0.05) after both DHR1 and DHR2, and that there was no significant difference in MVC loss between the two bouts. SOR was increased (p < 0.05) after DHR1, but was unchanged after DHR2. Mb concentration was elevated (p<0.05) after DHR1, with no further change (p>0.05) after DHR2. V̇O2, VE, RER, HR, RPE, LA, and SF were increased (p<0.05) for 72-96 hours after DHR1, but were elevated for only 24 hours after DHR2. Similarly, SL, ROM-A and ROM-K were decreased (p<0.05) for 72-96 hours after DHR1, but for only 24 hours after DHR2. It is concluded that DHR2 attenuated changes in markers of muscle damage, and in measures of physiological and biomechanical RE. We suggest that the attenuated changes in the physiological and biomechanical RE parameters after DHR2 may be related to the fact that less damage was caused by the second bout of exercise.