Instructed Squat Improves Limb But Not Knee Extensor Moment Symmetry In Individuals Following ACLr.

Abstract

Recent work found that individuals in early recovery post-ACL reconstruction (ACLr) spontaneously underload the surgical (Sx) limb and knee extensors in double limb tasks. With instructions to focus on equalizing weight under the feet, they are able to improve limb loading symmetry during a squat exercise. However, it is not known if these instructions can also improve knee extensor moment (kEXTmmt) symmetry. PURPOSE: To determine if instructions to equalize between limb loading improve kEXTmmt. METHODS: 14 subjects (6 male; 27 (11) yrs; 116.4 (16.6) days post-ACLr) performed bilateral squats to self-selected depths under natural (N) and instructed (I) conditions. In I condition, subjects were asked to concentrate on equalizing weight under both feet; no instructions were given in N condition. 3-D kinematics (250 Hz), ground reaction forces (1500 Hz), anthropometrics were used to calculate kEXTmmt (inverse dynamics). Vertical ground reaction force (vGRF) and kEXTmmt were averaged across the squat cycle for surgical (Sx) and non-surgical (NSx) limbs; 3 trials. The effect of instruction on vGRF and kEXTmmt was assessed using a (condition x limb) repeated measures ANOVA; post hoc paired t-test (p < 0.05). RESULTS: Condition x limb interaction was found (vGRF p = 0.007, kEXTmmt p = 0.002). Sx limb vGRF (Sx 335.29 (52.78) vs NSx 376.95 (67.75) N; p = 0.015) and kEXTmmt (Sx -0.33 (0.15) vs NSx -0.63 (0.17)Nm/kg; p < 0.001) were smaller in N condition. Sx limb kEXTmmt (Sx -0.35 (0.16) vs NSx -0.53 (0.15) Nm/kg; p = 0.002) was smaller in I condition; no difference was observed between limbs in vGRF. CONCLUSIONS: Individuals following ACLr adopt strategies that shift mechanical demands away from the knee of the surgical limb in early recovery. These strategies persist long term. Instruction to distribute weight symmetrically during squatting restored limb loading but did not restore kEXTmmt symmetry. These data suggest that these commonly employed corrective instructions are not adequate to retrain sagittal plane knee loading in early recovery post-ACLr.