Countermovement Jump Biomechanical Inefficiencies Independent Of Quadriceps Weakness In Athletes Returning To Sport After Anterior Cruciate Ligament Reconstruction

For athletes returning to sport after ACL reconstruction, comparing ground reaction force (GRF) metrics during countermovement jumps (CMJ), in addition to isokinetic quadriceps strength testing, may reveal between-limb asymmetries and aid in clinical decision making. PURPOSE: To compare the GRF metrics from bilateral and unilateral CMJs, as well as isokinetic quadriceps strength, between the involved and uninvolved limbs in patients who have had ACLR and were undergoing return to sport testing. METHODS: Twenty-two patients who had undergone ACLR (time since surgery: 9.8 ± 3.6 months) underwent isokinetic tests of knee extension strength and power and performed bilateral and unilateral CMJs on force plates. CMJ performance metrics (2) and metrics from the unweighting (2), braking (7) and propulsive phases (4) were compared between limbs using paired t-tests. Associations between asymmetries in CMJ metrics and isokinetic strength and power were assessed using Pearson correlation analysis. RESULTS: During bilateral CMJs, asymmetries were evident for 3 braking phase metrics (13% lower force at low position, 16% lower RFD, 16% lower eccentric force) and 2 propulsive phase metrics (13% lower mean propulsive force, 11% lower peak propulsive force). During unilateral CMJs, asymmetries were evident for 1 unweighting phase metric (11% less unweighting), 4 braking phase metrics (9% less countermovement depth, 16% lower peak braking power, 4% lower force at low position, 13% lower eccentric force), 3 propulsive phase metrics (13% lower peak propulsive power, 5% lower mean propulsive force, 6% lower peak propulsive force) and both performance metrics (20% lower jump height, 13% lower RSI). The involved quadriceps were 24±19% weaker than the uninvolved side (p<0.001). Asymmetry in knee extension strength was not correlated with any of the bilateral CMJ asymmetry metrics and only 2 of the unilateral CMJ asymmetry metrics (r = 0.513, 0.524). Asymmetry in knee extension power correlated with 3 bilateral CMJ asymmetry metrics (r = 0.436-0.516) and 3 unilateral CMJ asymmetry metrics (r = 0.468-0.607). CONCLUSION: Comparison of GRF profiles revealed deficits on the involved side during both types of CMJ. These deficits indicate impaired stretch-shortening cycle function and were mostly independent of quadriceps weakness.