Ground reaction force profiles during inclined running at iso-efficiency speeds

While running provides an accessible form of cardiovascular stimulus, many runners report lower extremity musculoskeletal injuries. Additionally, runners who develop overuse injuries, such as tibial stress fractures, also have higher loading rates (LR) and impact forces. Therefore, the purpose of this study was to investigate how uphill treadmill running at iso-efficient speeds (IES; a speed-incline combination having the same metabolic intensity as level running) influences impact LR, and peak vertical ground reaction forces (GRF). Eleven collegiate distance runners completed 3 experimental running conditions (0%, 4%, and 8% treadmill inclination). During each running condition, the metabolic intensity was controlled by implementing an IES for each runner. All variables of interest were significantly reduced as treadmill incline increased (0% > 4% > 8%). Incline running is more metabolically demanding compared to level running at the same speed. But, if speed is controlled to maintain metabolic output, runners could decrease LR and peak vertical GRF while achieving the same metabolic training stimulus as level running.