Whole-body biomechanical load in running-based sports: the validity of estimating ground reaction forces from segmental accelerations

Objectives Unlike physiological loads, the biomechanical loads of training in running-based sports are still largely unexplored. This study, therefore, aimed to assess the validity of estimating ground reaction forces (GRF), as a measure of external whole-body biomechanical loading, from segmental accelerations. Methods Fifteen team-sport athletes performed accelerations, decelerations, 90° cuts and straight running at different speeds including sprinting. Full-body kinematics and GRF were recorded with a three-dimensional motion capture system and a single force platform respectively. GRF profiles were estimated as the sum of the product of all fifteen segmental masses and accelerations, or a reduced number of segments. Results Errors for GRF profiles estimated from fifteen segmental accelerations were low (1–2 N kg−1) for low-speed running, moderate (2–3 N kg−1) for accelerations, 90° cuts and moderate-speed running, but very high (>4 N kg−1) for decelerations and high-speed running. Similarly, impulse (2.3–11.1%), impact peak (9.2–28.5%) and loading rate (20.1–42.8%) errors varied across tasks. Moreover, mean errors increased from 3.26 ± 1.72 N kg−1 to 6.76 ± 3.62 N kg−1 across tasks when the number of segments was reduced. Conclusions Accuracy of estimated GRF profiles and loading characteristics was dependent on task, and errors substantially increased when the number of segments was reduced. Using a direct mechanical approach to estimate GRF from segmental accelerations is thus unlikely to be a valid method to assess whole-body biomechanical loading across different dynamic and high-intensity activities. Researchers and practitioners should, therefore, be very cautious when interpreting accelerations from one or several segments, as these are unlikely to accurately represent external whole-body biomechanical loads.