Abstract
PURPOSE: Ground reaction forces (GRF) data have been introduced to enhance the understanding of anterior cruciate ligament (ACL) injury pathomechanics. However, translating GRF information into daily clinical practice remains challenging for high-demanding movements such as cutting manoeuvres. This study aims to describe GRF of the 90° change of direction (COD) task, providing robust benchmark data and force-time curve description to enhance their use in clinical practice, particularly ACL injury prevention. METHODS: One thousand and two healthy football (soccer) players (16.3 ± 2.8 years, 264 females) performed three preplanned 90° COD tasks per limb at maximum intensity, with the cutting foot contact performed on an artificial turf floor embedded force platform (AMTI), which collected GRF data (frequency: 1000 Hz). Peak GRF (impact and propulsion phases, and their ratio), ground contact time, rate of force acceptance (RFA), impulse were presented as absolute values and normalised to body weight (BW). Differences in kinetics metrics according to sex, level of play, limb dominance were determined via Student's t-test (p < 0.05). Multiple linear regression analyses determined the association between players' characteristics and kinetics. RESULTS: Six thousand and eight valid attempts were included. Vertical GRF was 1516 ± 526 N (2.48 ± 0.79 N/BW) and occurred 32.6 ms after initial contact (10.4% of the cut stance). Vertical RFA was 95,200 ± 48,138 N/s (155.6 ± 75.5 N/s/BW). Male players had higher absolute and normalised GRFs and vertical RFA than females (p < 0.001). Elite players had smaller impulse: propulsion ratio than subelite players (p < 0.001). The regression showed limited variance of GRF metrics (adjusted-R(2) = 0.047-0.014, p < 0.001). CONCLUSION: Normative data and explanation of clinically relevant GRF features were provided. GRF features could enrich the understanding of players' COD movement quality and performances. Sports medical and performance practitioners may include the analysis of GRF during COD as part of athlete screening for participation, injury risk and return to play, potentially offering insights for ACL (re)injury risk mitigation. LEVEL OF EVIDENCE: Level IV, cohort study.