Effects of Cross-Education After 6 Weeks of Eccentric Single-Leg Decline Squats Performed With Different Execution Times: A Randomized Controlled Trial

Abstract

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Background: Cross-education of strength refers to the strength gain that is transferred to the contralateral limb after a unilateral training program. Hypothesis: Unilateral eccentric training using different muscle contraction times would improve the structural and functional properties of the untrained contralateral limb. Study Design: Randomized controlled trial. Level of Evidence: Level 2. Methods: Thirty-six participants were randomized into a control group, experimental group 1 (EG6s; eccentric contraction runtime = 6 seconds) and experimental group 2 (EG3s; eccentric contraction runtime = 3 seconds). The thickness and elastographic index of the patellar tendon (PT), lean mass and fat percentage of the thigh, contractile properties of the vastus lateralis (VL), as well as isometric, concentric, and eccentric knee extensor peak torques, and eccentric single-leg decline squat (SLDSe) 1 repetition maximum (1-RM) were measured after 6 weeks of SLDSe training (3 times per week, 80% of 1-RM) and after 6 weeks of detraining in the untrained contralateral limb. Results: After training, there was an increase in lean thigh mass of the untrained limb in both groups: EG6s (0.17 ± 0.29 kg; P = 0.03; effect size [ES] = 0.15) and EG3s (0.15 ± 0.23 kg; P = 0.04; ES = 0.19). Likewise, both EG6s (62.30 ± 19.09 kg; P < 0.001; ES = 4.23) and EG3s (68.09 ± 27.49 kg; P < 0.001; ES = 3.40) increased their 1-RM, isometric (EG6s: 48.64 ± 44.82 N·m, P < 0.001, ES = 0.63; EG3s: 34.81 ± 47.30 N·m, P = 0.004, ES = 0.38), concentric at 60 deg/s and 180 deg/s and eccentric at 60 deg/s and 180 deg/s knee extensor peak torques (P < 0.05) in the untrained limb. However, no differences were found in the contractile properties of the VL or in the thickness of the PT after eccentric training in either of the 2 experimental groups. Conclusion: Regardless of the runtime of the contraction, 6 weeks of SLSDe was effective for inducing structural and strength adaptations in the contralateral untrained limb. However, most of these adaptations were lost after 6 weeks of detraining. Clinical Relevance: Our study suggests that cross-education training can be of great importance for clinical application and musculoskeletal and neuromuscular rehabilitative processes after unilateral injury.