Beware of the 'moving target' - uninvolved limb strength increases to exceed pre-operative values during rehabilitation after ACL reconstruction in male professional and recreational athletes.

OBJECTIVE: To describe the changes in quadriceps and hamstrings muscle strength in the uninvolved limb of male professional and recreational athletes during rehabilitation after ACLR and compare to preoperative strength values. DESIGN: Prospective longitudinal study. METHODS: During rehabilitation, 665 participants who underwent unilateral ACLR performed a strength test preoperatively and every 6 weeks after surgery for up to 9 months. Isokinetic quadriceps and hamstrings strength of the uninvolved limb were measured at an angular velocity of 60°/s and normalized to body weight (Nm/kg). RESULTS: Quadriceps and hamstrings strength of the uninvolved limb gradually increased during rehabilitation until 6 months post-ACLR, and plateaued thereafter. Postoperative quadriceps' strength significantly exceeded preoperative values by 3 months for professional (2.99 Nm/kg, CI 95% 2.93-3.04, p=0.007) and by 6 months for recreational athletes (2.77Nm/kg, CI 95% 2.71-2.83, p<0.001), and hamstrings exceeded pre-surgery levels by 4.5 months (1.71Nm/kg, CI 95% 1.67-1.74, p<0.001 and 1.43 Nm/kg, CI 95% 1.40-1.46, p=0.002, professional and recreational athletes respectively). CONCLUSION: In male professional and recreational athletes, uninvolved limb quadriceps and hamstrings strength gradually improved after ACLR, until 6 months after surgery. The uninvolved limb's strength may present as a 'moving target' that requires consistent monitoring during rehabilitation.