Downhill running impairs peripheral but not central neuromuscular indices in elbow flexor muscles

Abstract The purpose of this study was to examine the effects of a 1-hour downhill running exercise on the elbow flexor muscles’ neuromuscular functions. Seventeen adults (Control [CON]: n = 9; Experimental [EXP]: n = 8) completed this study. The CON rested for 30 minutes while the EXP performed the downhill running. Before, 10 minutes, 24 hours, and 48 hours after the interventions, dependent variables (knee extensor muscle soreness, elbow flexion and knee extension isometric strength, elbow flexion resting twitch and voluntary activation [VA], and the biceps surface electromyography [EMG] amplitude) were measured. Knee extensor muscle soreness was significantly greater in the EXP than the CON group following the intervention throughout the entire 48 hours. This was accompanied by the greater decline in the knee extension strength in the EXP than the CON (mean ± SD: -6.9 ± 3.4% vs. 1.0 ± 3.2%, p = 0.044). The elbow flexion strength, VA, and EMG amplitude were not affected by the exercise. However, the decline of the elbow flexion resting twitch was greater in the EXP than the CON (-19.6 ± 6.3% vs. 8.7 ± 5.9%, p = 0.003). Therefore, the downhill running impaired the remote elbow flexor muscles at a peripheral level.