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

Abstract

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 5 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˚(95% CI [0.09, 0.27] N•m•kgBM 21 , d 5 0.60), 30( 95% CI [0.25, 0.48] N•m•kgBM 21 , d 5 0.82), 45˚(95% CI [0.32, 0.58] N•m•kgBM 21 , d 5 0.78), and 75˚(95% CI [0.18, 0.46] N•m•kgBM 21 , d 5 0.54) knee flexion. Involved limb knee extensor net joint moment work in sit-to-stand (95% CI [0.034, 0.135] J•kgBM 21 , d 5 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.

“Knees Out” or “Knees In”? Volitional Lateral vs. Medial Hip Rotation During Barbell Squats

“…Therefore, even if the multivariate ANOVA, univariate ANOVA, and Bonferroni's corrected t-test were all significant, but the difference was less than the minimum effect worth detecting, the difference would not be considered as meaningful. The importance of establishing the minimum effect worth detecting is based on recent experimental studies comparing exercises that have found no difference in training adaptations even when moderate effect size biomechanical differences exist between the exercises (6,9,15,16).…”

“…In some exercises, horizontal forces are also present in the interface between the weight and the lifter (28,29). The combination of 3D limb kinematics and triaxial forces is required to understand joint loading and muscular requirements during resistance exercise (5), which, combined with training intervention studies, provides evidence to support or refute the use of different variations (1,9,13,16,22).…”

“…For example, atrophy of the 3 vasti muscles, but not the rectus femoris, occurs following anterior cruciate ligament injury (26,38). Consequently, squat exercise, which elicits vasti muscles but not rectus femoris hypertrophy may be valuable for restoring knee extensor strength for these individuals (16,22).…”