Knee Extensor Strength in Anterior Cruciate Ligament-Deficient Individuals Following Normal and Modified Squats: A Randomized Controlled Trial

Jean, LMY, Gross, DP, and Chiu, LZF. Knee extensor strength in anterior cruciate ligament-deficient individuals following normal and modified squats: a randomized controlled trial. J Strength Cond Res 36(1): 47-54, 2022-Training with barbell squats, which load the quadriceps, increases knee extensor strength. Anterior cruciate ligament (ACL) injury results in a quadriceps avoidance substitution strategy, which may impair the efficacy of barbell squat training. Modified squats to promote quadriceps loading have been proposed to facilitate restoring knee extensor strength and function. This research compared resistance training using traditional squats (TRAD) versus traditional plus modified squats (EXP) in ACL-deficient individuals. Thirty-seven ACL-deficient individuals were randomly assigned to TRAD or EXP. Knee extensor function was assessed using maximum isometric strength testing and 3D motion analysis of sit-to-stand. Effect sizes for minimum meaningful improvement were established (d = 0.28-0.47). There were no significant differences between TRAD and EXP for knee extensor strength before, in response to, or after the training interventions (p > 0.05). Involved limb knee extensor strength increased at 15 degrees (95% CI [0.09, 0.27] N center dot m center dot kgBM(-1), d = 0.60), 30 degrees (95% CI [0.25, 0.48] N center dot m center dot kgBM(-1), d = 0.82), 45 degrees (95% CI [0.32, 0.58] N center dot m center dot kgBM(-1), d = 0.78), and 75 degrees (95% CI [0.18, 0.46] N center dot m center dot kgBM(-1), d = 0.54) knee flexion. Involved limb knee extensor net joint moment work in sit-to-stand (95% CI [0.034, 0.135] J center dot kgBM(-1), d = 0.48) increased in both groups. Squat training was effective for increasing involved limb isometric knee extensor strength and knee extensor work performed in the sit-to-stand. Modified squats do not seem to provide additional benefit.

Automated summary

This study compared the effects of normal squats and modified squats in individuals with ACL deficiency, and the results showed no significant difference between the two training methods in terms of knee extensor strength and function.