The moderating effect of tibialis anterior fatigue protocol on the relationships between rearfoot eversion, thigh muscle activation, and knee internal rotation during a single leg forward jump stop task

Objective. To examine the moderating effect of tibialis anterior muscle fatigue protocol on the relationships between rearfoot eversion, thigh muscle activation, and knee internal rotation during a single leg forward jump stop task. Subjects. 72 recreationally active healthy individuals (age = 23.8, ht = 168.9cm, and mass = 70.9kg). Methods . Subjects performed a single leg forward jump stop task before and after a tibialis anterior muscle (TA) fatiguing protocol. TA fatigue was induced through dorsiflexion exercise by lifting 5% of subject's body weight using a pulley system. During the jump stop task, kinematic and thigh muscle activation data were obtained using an electromagnetic tracking system and surface electromyography (sEMG). Knee internal rotation excursion (KIRexc), rearfoot eversion excursion at peak knee internal rotation (EVKIRexc), and sEMG percent RMS amplitudes of vastus lateraris (%VL), biceps femoris (%BF), and semitendinosus (%ST) 150ms before touch down were obtained during the jump stop task before and after the fatiguing protocol. Path analyses examined the extent to which EVKIRexc and thigh muscle activations predicted KIRexc in pre- and post-fatigue conditions. A paired sample t-test examined if TA fatigue would increase total rearfoot eversion (EVexc) and KIRexc in the post-fatigue condition as compared to the pre-fatigue condition. Results. TA fatigue did not increase EVexc or KIRexc. Path analyses revealed that although no relationships were found between EVKIRexc, %VL, BF, or ST and KIRexc in the pre-fatigue condition, %VL was significantly related with KIRexc in post-fatigue condition. Conclusions. The primary results revealed that TA fatigue did not change either rearfoot eversion or knee internal rotation motion, and the only association found was between post-fatigue quadriceps muscle activation and knee internal rotation motion. Considering the ACL injury mechanism, these findings support the importance of preventing excessive quadriceps contraction to prevent excessive knee internal rotation, but calls into question the theoretical connection between excessive rearfoot eversion, increased knee internal rotation, and ACL injury risk. However, these findings are limited to a single leg forward jump stop task, and the theoretical connections between rearfoot eversion, knee internal rotation and ACL injury risk during other functionally relevant dynamic tasks should be evaluated.