Relationship between electromyographic activity of knee joint muscles with vertical and posterior ground reaction forces in anterior cruciate ligament reconstructed patients during a single leg vertical drop landing task.

The objective of the present study is to examine the relation between activity patterns of knee joint muscles with vertical and posterior ground reaction forces (VGRF and PGRF, respectively) in patients after anterior cruciate ligament reconstruction (ACLR). Twenty males post-ACLR participated in this cross-sectional study. The association between muscle activity with VGRF and PGRF was assessed during a single leg vertical drop-landing task. There were strong negative associations between preparatory VL, VM and MG activity and PGRF (P< 0.05). Strong positive associations were found between reactive VM and LH activity with PGRF (P< 0.05). Preparatory co-activation of VM: MH had significant negative associations with VGRF (P< 0.05) and reactive co-activation of VL:LH had a significant positive relation with PGRF(P< 0.05). Greater preparatory activity and co-activation of knee muscles were associated with lower peak PGRF and VGRF, whereas greater reactive activity and co-activation of knee muscles was associated with greater peak PGRF and VGRF. According to our findings, both activity and co-activation of knee muscles during the preparatory phase were associated with reduced PGRF and VGRF, respectively in ACLR patients; thus, incorporating exercises in order to increase preparatory activity and co-activation of knee joint muscles into rehabilitation programs in ACLR patients seems necessary.