The ground reaction force (GRF) is known to produce tibial internal rotation loading associated with the stress in the anterior cruciate ligament (ACL). However, it is unclear whether the friction moment (FM; the moment due to horizontal shoe-floor friction, acting around the vertical axis at the GRF acting point) facilitates or restrains the effect of GRF-driven tibial rotation loading during cutting. The 45° cutting motions with forefoot/rearfoot strikes were captured simultaneously with GRF and FM data from 23 healthy males. The FM- and GRF-driven tibial rotation moments were calculated. Time-series correlation between FM- and GRF-driven tibial rotation moments and the orientation relationship among those moment vectors was investigated. The FM-driven tibial rotation moment negatively correlated with the GRF-driven one within the first 10% of stance phase. The peak regression slope value was -0.34 [SD 0.33] for forefoot and -1.64 [SD 1.76] for rearfoot strikes, showing significant difference from zero (SPM one-sample t-test, p<0.05). The FM-driven tibial "external" rotation moment counteracted the GRF-driven tibial "internal" rotation moment within first 10% of the stance phase in most trials, suggesting that the FM-driven tibial rotation moment potentially diminishes the effect of GRF-driven one and may reduce ACL injury risk during cutting.
Keywords: Friction moment; anterior cruciate ligament injury; deceleration motion; free moment; tibial rotation.