Hip and Knee Bilateral Deficit Across Bilateral, Unilateral, and Split-Load Leg Press Conditions

Objectives: This study investigated bilateral strength asymmetry, the bilateral asymmetry index, and the bilateral deficit ratio during one-repetition maximum leg press testing performed under bilateral, unilateral, and split-load conditions and examined their associations with isokinetic knee and hip strength asymmetries. Methods: 31 resistance-trained males completed 1RM leg press tests in all loading modes, followed by isokinetic knee flexion/extension and hip extension assessments at 60°·s^-1. Results: The repeated measure ANOVA showed that split-load leg press had a significantly greater bilateral deficit ratio (14.29 ± 7.71%) compared to the bilateral condition (5.16 ± 9.60%, p < 0.001). Isokinetic testing showed significant inter-limb differences for knee flexion and extension but not hip extension. The bilateral strength asymmetry varied across tasks (5.17 ± 4.44% in leg press to 17.84 ± 12.40% in eccentric hip extension), while bilateral asymmetry index remained consistently lower. Bilateral strength asymmetry differed significantly across leg press conditions, whereas the bilateral asymmetry index did not. Knee flexion bilateral asymmetry index correlated with dominant and non-dominant hamstring to quadriceps ratios (respectively, r = 0.61; r = 0.37) and cross-limb flexor-extensor ratios (r = 0.42). No significant relationships were found for hip extension asymmetry. Conclusions: Split-load leg press might be used to test lower limb bilateral deficit, because it provides easily detectable deficit values. Unilateral leg press might be used to detect lateral strength differences, since it provides relation to isokinetic strength of knee flexors and extensors.