(32) EFFECT OF 8 WEEKS OF INERTIAL ONE-LEG SQUAT ON DROP JUMP BIOMECHANICS IN ATHLETES WITH ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION AFTER RETURN TO SPORT

Athletes with anterior cruciate ligament reconstruction (ACLR) display altered jumping biomechanics years after surgery, possibly due to reduced knee function. Given the high occurrence of ACL injuries, strength coaches are likely confronted to the particular needs of athletes with ACLR. Yet, methods to improve jumping biomechanics after ACLR are lacking. Therefore, we created a new intervention combining eccentric-accentuation with deep knee flexion until exhaustion in the reconstructed leg. We hypothesized that jump height would increase, hip relative contribution decrease, and knee contribution increase in the reconstructed leg.

Purpose: To evaluate changes in drop jump biomechanics following 8-weeks of deep-knee flexion, exhaustive inertial rear–leg elevated split squat (Bulgarian squat) in athletes with ACLR.

Method: 11 athletes with ACLR who had returned to sport (8 females, 3 males; 20.8±2.7 y.o., 1.71±0.09 m, 67.3±11.2 kg, 546±270 days from surgery) performed 16 sessions of exhaustive deep knee flexion Bulgarian squat in the injured leg using a flywheel training device. We recorded three single-leg 30-cm drop jumps (DJ) before and after training using a 3D motion capture system and force platform. All data were normalized by the participant’s mass. Pre-planned comparisons included jump height (from impulse during propulsion), hip, knee, and ankle relative contributions (% of the three joints' work). Other variables included peak vertical ground reaction force, impulse, contact duration, peak knee flexion and valgus angles. Pre-planned comparisons were analyzed using one-tailed paired t-test. Other variables were evaluated with 2-way ANOVA (Time × Leg) and post hoc paired t-test. Effect size was measured with Cohen’s d (d < 0.20: small, d < 0.50: medium, d < 0.80: large effect).

Results: Jump height increased by 2.47±4.68 cm (p = .02, d = 0.75), knee contribution during DJ increased (5.2±7.0%, p = .03, d = 0.63) and hip contribution decreased significantly (-7.5±11.8%, p = .02, d = 0.68) in the reconstructed leg only (see figure). Reconstructed leg’s total impulse increased by 0.20±0.32 N·s/kg (p = .03, d = 0.76). Propulsion duration decreased in both legs (reconstructed: -42.4±77.6 ms, p = .03, d = 0.74; intact: -43.2±71.1 ms, p = .02, d =0.81). Peak knee angle decreased by 5.1±8.8° (p = .02, d = 0.82) on the intact leg, decreasing interlimb difference from 7.1±10.1° (p = .03, d = 0.76) to 2.7±7.4° (p = .19, d = 0.42).

Conclusion: Our intervention improved jump height in the uninjured leg only, where knee joint relative contribution increased and hip joint contribution decreased. These changes resulted from greater force production over a shorter time, notably in the propulsion phase. PRACTICAL APPLICATIONS: Adding a single set of deep knee flexion, exhaustive flywheel Bulgarian squat in the reconstructed leg is a time efficient way to improve the particular DJ biomechanics in athletes with ACLR after return to sport.

Acknowledgements: The authors would like to express their gratitude to Shin Takayama and Wakana Sasakabe for their help in conducting the experiment. The authors have no conflict of interest to declare.