Validity Of Between-limb Symmetry For Insole Sensors During Daily Activities

Restoring loading symmetry is often a target of recovery after neurologic and musculoskeletal injuries. Current understanding of lower extremity loading is limited to laboratory data collections using force plates. Understanding loading behaviors in natural environments is critical to translate laboratory findings to real life. PURPOSE: To assess the concurrent validity between force plates and insole sensors for between-limb loading symmetry across activities performed continuously that represent daily tasks including gait at various speeds. METHODS: Twelve participants (6 Female; 74.6 ± 18 kg; 1.73 ± 0.1 m) performed daily loading tasks on a treadmill instrumented with two force plates across two days while wearing loadsol insole sensors. Vertical ground reaction forces (vGRF) were recorded concurrently while participants performed a single limb stance (SLS; 30 second each limb) and a randomized series of tasks including walking, reaching high and low, shifting weight and standing. Body weight was calculated as the mean during the middle 10 seconds of SLS. Loading was analyzed across 12 minutes of repetitive tasks and was considered with and without normalization by body weight quantified by SLS insole data. Between-limb symmetry (BLS) was calculated as the ratio between left and right force impulse (area under the vGRF time curve) for both systems. Intraclass correlation coefficients (ICC3,k) were used to assess validity of SLS body weight, BLS, and normalized BLS (BLSN). Average between system differences and limits of agreement (LOA) were calculated. RESULTS: ICC results were excellent for SLS (0.99, p < 0.001), poor for BLS (0.46 p = .07) and moderate for BLSN (0.66, p = 0.006). Bias were 6.26 N, -0.014, and 0.02, and LOA were (-62, 74.5), (-0.11, 0.08), and (-0.05, 0.09) for SLS, BLS and BLSN, respectively. CONCLUSION: Loadsols are a valid tool for quantifying symmetry between limbs for loading throughout the day. These results validate the use of these insoles in ecological settings. Despite excellent agreement between systems for vGRF during SLS, LOA were up to 15% of body weight. Poor BLS ICC could be attributed to combined error between sensors. Improved BLSN suggests that normalizing insole vGRF by SLS values is necessary for interpretation of daily loading deficits.