How Do Individuals Following Anterior Cruciate Ligament Reconstruction Load Their Limbs Outside The Laboratory?

PURPOSE/HYPOTHESIS: Individuals following anterior cruciate ligament reconstruction (ACLr) underload the surgical limb by shifting demand to the opposite limb during bilateral tasks.1,2 This strategy persists long-term and in the absence of joint level impairments.1–3 Daily activities may provide a strong stimulus for the development and maintenance of underloading strategies through a large volume of repetitive practice. However, it is not known if individuals following ACLr underload the surgical limb throughout the day. The purpose of this study is to investigate individuals' loading behaviors throughout the day post ACLr and to determine how daily loading relates to the loading during bilateral tasks. NUMBER OF SUBJECTS: Seven post-ACLr (111 ± 16 days). A larger sample size will be available for presentation at CSM 2018. MATERIALS/METHODS: Participants performed 4 trials of bilateral squats while standing on 2 force platforms (BTS, Milan, Italy; 1000 Hz). Vertical ground reaction forces (vGRF) were collected under each limb. Following laboratory testing participants wore a pair of plantar pressure insoles (Orpyx, Calgary, Canada; 100 Hz and Moticon, Munich, Germany; 25 Hz) for 5 hours during daily activities. Vertical force (vF) was calculated for each insole using previously validated methods.4,5 vGRF impulse (squat) and vF impulse (daily activities) were calculated as the area under the vGRF and vF time curves, respectively. Loading symmetry indices during squat (LSIlab) and during daily activities (LSIday) were calculated as a ratio of surgical/nonsurgical for vGRF and vF impulses, respectively. Paired t tests were used to determine if vGRF during squat and vF in daily activities differed between limbs. Pearson productmoment correlation was used to determine if loading symmetry during daily activities LSIday was related to symmetry during squat (LSIlab) (α = .05). RESULTS: On average, individuals following ACLr exhibited lower vGRF impulse during bilateral squat (surgical, 0.92 ± 0.17 versus nonsurgical, 1.10 ± 0.19 N·s; P = .05; ES, 0.88) and lower vF impulse in daily activities (surgical, 0.89 ± 0.17 versus nonsurgical, 1.01 ± 0.23 N·s; P = .02; ES, 1.13) in the surgical limb compared to the nonsurgical limb. Loading symmetry indices during squat (LSIlab) and during daily activities (LSIday) were positively correlated (r = 0.86, P = .01). CONCLUSIONS: While average loading differences between limbs were observed, individual data suggest that some individuals 111 days post ACLr preferentially underloaded the surgical limb during bilateral squat and daily activities while others do not. Positive relationship between LSIlab and LSIday suggests that those who underload the surgical limb throughout the day also underload during a task that would be considered submaximal at this time post ACLr (squat). The loading strategy observed in the laboratory is reflected in individuals' daily loading behaviors. CLINICAL RELEVANCE: Understanding how daily behaviors relate to the persistence of underloading strategies