Muscle utilisation in squat exercise depends on technique. The purpose of this study was to compare net joint moments (NJMs) and muscle activation during squats without and with restricted leg dorsiflexion. Experienced men (n = 5) and women (n = 4) performed full squats at 80% one repetition maximum. 3D motion analysis, force platform and (EMG) data were collected. Restricting anterior leg rotation reduced anterior leg (P = 0.001) and posterior thigh (P < 0.001) rotations, resulting in a smaller knee flexion range of motion (P < 0.001). At maximum squat depth, ankle plantar flexor (P < 0.001) and knee extensor (P < 0.001) NJM were higher in unrestricted squats. Hip extensor NJM (P = 0.14) was not different between squat types at maximum squat depth. Vastus lateralis (P > 0.05), vastus medialis (P > 0.05) and rectus femoris (P > 0.05) EMG were not different between squat types. Unrestricted squats have higher ankle plantar flexor and knee extensor NJM than previously reported from jumping and landing. However, ankle plantar flexor and knee extensor NJM are lower in restricted squats than previous studies of jumping and landing. The high NJM in unrestricted squat exercise performed through a full range of motion suggests this squat type would be more effective to stimulate adaptations in the lower extremity musculature than restricted squats.

Jean, LMY and Chiu, LZF. Elevating the noninvolved limb reduces knee extensor asymmetry during squat exercise in persons with reconstructed anterior cruciate ligament. J Strength Cond Res 34(8): 2120–2127, 2020—Anterior cruciate ligament (ACL)–injured individuals use less knee extensor net joint moment (NJM) in the involved vs. noninvolved limb during squat exercises. The objective of this research was to examine if knee extensor NJM symmetry between the involved and noninvolved limbs could be attained with a modified squat. Six individuals with unilateral ACL reconstructed knees performed bilateral squats under normal conditions and with their noninvolved limb elevated on a 5-cm platform. Knee extensor NJM was determined using 3-dimensional motion analysis. Knee extensor NJM was lower in the involved compared with the noninvolved limb (95% confidence interval [CI], 0.08–0.28 N·m·kg−1; d = 1.66 SD) during normal squats. Knee extensor NJM was greater in the involved (95% CI, 0.02–0.18 N·m·kg−1; d = 0.57 SD) and lower in the noninvolved (95% CI, −0.25 to −0.07 N·m·kg−1; d = 1.85 SD) limbs in the elevated vs. normal squats. Knee extensor NJM was not different between limbs when the noninvolved limb was elevated (95% CI, −0.26 to 0.11 N·m·kg−1; d = 0.48 SD). Persons with ACL reconstruction exhibit knee extensor asymmetry during bilateral squats. Elevating the noninvolved limb reduces knee extensor NJM asymmetry between the involved and noninvolved limbs during squat exercise.

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.

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