Cross‐education improves quadriceps strength recovery after ACL reconstruction: a randomized controlled trial

Abstract Purpose The aim of this study was to investigate the effects of concentric and eccentric cross‐education (CE) on quadriceps strength and knee function recoveries after anterior cruciate ligament (ACL) reconstruction. Methods Forty‐eight patients (age: 29.5 ± 6.8 years, body mass index: 26.1 ± 3.2 kg/m 2 ) who had undergone ACL reconstruction with hamstring tendon autograft were included in the study. The patients were randomly divided into three groups when they reached four weeks post surgery: (1) concentric CE ( n = 16); (2) eccentric CE ( n = 16); and (3) control ( n = 16). All groups followed the same post‐surgical rehabilitation program for their reconstructed limb. Additionally, the two experimental groups followed eight weeks of isokinetic training for the uninjured knee at 60°/s for 3 days per week. Quadriceps maximum voluntary isometric strength (MVIC) was measured during the 4th week (pre‐training), 12th week (post training), and 24th week post surgery. The single‐leg hop distance and International Knee Documentary Committee (IKDC) scores were also evaluated during the 24th week post surgery. Analysis of variance was used for statistical analysis. Results Group‐by‐time interaction was significant for quadriceps MVICs for reconstructed and healthy limbs ( p = 0.02). Quadriceps strength of both knees was greater in concentric and eccentric CE groups compared to control group during the 12th‐ and 24th weeks post surgery ( p < 0.05). Strength gain was 28% and 31% in concentric and eccentric CE groups, respectively, when compared with the control group. Concentric and eccentric CE had similar effects on quadriceps strength recovery (n.s.). IKDC score, and single‐leg hop distances were not significantly different among groups (n.s.). Conclusions Concentric and eccentric quadricep strengthening of healthy limbs in early phases of ACL rehabilitation improved post‐surgical quadriceps strength recovery of the reconstructed limb. CE should be integrated into ACL reconstruction rehabilitation, especially in the early rehabilitative phases to restore quadriceps strength. Level of evidence Randomized controlled trial, Level I.