Comparison of the correlations between impact loading rates and peak accelerations measured at two different body sites: Intra- and inter-subject analysis

Background: High average (VALR) and instantaneous vertical loading rates (VILR) during impact have been associated with many running-related injuries. Peak acceleration (PA), measured with an accelerometer, has provided an alternative method to estimate impact loading during outdoor running. This study sought to compare both intra- and inter-subject correlations between vertical loading rates and PA measured at two body sites during running. Methods: Ground reaction force data were collected from 10 healthy adults (age = 23.6 ± 3.8 years) during treadmill running at different speeds and inclination surfaces. Concurrently, PAs at the lateral malleoli and the distal tibia were measured using synchronized accelerometers. Results: We found significant positive intra-subject correlation between loading rates and PA at the lateral malleoli (r = 0.561–0.950, p < 0.001) and the distal tibia (r = 0.486–0.913, p < 0.001). PA measured at the lateral malleoli showed stronger correlation with loading rates (p = 0.004) than the measurement at the distal tibia. On the other hand, inter-subject variances were observed in the association between PA and vertical loading rates. The inter-subject variances at the distal tibia were 3.88 ± 3.09 BW/s and 5.69 ± 3.05 BW/s in VALR and VLIR respectively. Similarly, the inter-subject variances in the measurement at lateral malleoli were 5.24 ± 2.85 BW/s and 6.67 ± 2.83 BW/s in VALR and VLIR respectively. Conclusions: PA measured at lateral malleoli has stronger correlation with VALR or VILR than the measurement at distal tibia. Caution is advised when using PA to conduct inter-subject comparisons of vertical loading rates during running.