Can Level Ground Biomechanics Predict Uphill and Downhill Running Economy?

Marathon terrain significantly impacts athlete performance. This study examined whether level running biomechanics can predict uphill and downhill running economy using a new metric, running grade aptitude (RGA). Forty distance runners (32 males and 8 females) ran on a split-belt treadmill at +4% and −4% gradients, simulating Boston Marathon hills. We assessed stride parameters, foot strike patterns, ground reaction forces, and oxygen consumption during uphill, downhill, and level running. RGA was determined by analyzing the slope of the relationship between oxygen uptake and treadmill grade, categorizing runners as preferring uphill RGA, downhill RGA, or negligible RGA. We found a significant correlation ( R 2  = .44) between active peak vertical ground reaction forces during level running and downhill running economy (downhill RGA). However, no other variables significantly related to RGA, and no difference in RGA was observed between genders. The study suggests that runners who generate higher peak vertical ground reaction forces during level running are more economical on downhill segments. These findings highlight the importance of individual biomechanical traits in optimizing training and racing strategies for distance runners.