Limb Loading Asymmetry During Simulated Daily Functional Tasks

The threshold of 10% symmetry has been proposed as an expected level of limb difference in healthy populations. While this threshold has been used to evaluate both clinical and athletic populations, questions remain about the expected level of symmetry in healthy populations. PURPOSE: To determine differences in load symmetry in healthy young adults during 4 activities of daily living: level walking (LW), sit to stand (STS), stair ascent (SA) and stair descent (SD). We hypothesized the peak impact force symmetry would not exceed 10% for any functional task. METHODS: 72 healthy young adults were enrolled in this IRB approved study. A load sensing insole was fit into athletic shoes for each participant. Plantar loading data was collected at 200 Hz while participants completed 7 trials for each of the 4 tasks. Peak impact force (PIF) was found bilaterally for each trial using MATLAB and were used to calculate limb symmetry (ASI, LSI, NSI). A χ^2 analysis was conducted using RStudio (R, ver 4.3.1, Boston, MA, USA) to determine the appropriateness of the 10% threshold for each task. RESULTS: As Figure 1 shows, results indicate the mean and median PIF symmetry values for each task were all below the 10% threshold. The STS task had the highest asymmetry (mean LSI = 8.55%), while LW had the lowest asymmetry (mean LSI = 4.58%). The PIF symmetry values for LW, SA, and SD were all found to have a χ^2 value below the critical threshold (χ^2 = 3.84,α = 0.05), however, the χ^2 values for the STS task were above the critical threshold (χ^2 = 110.0,110.0,121.7 for the ASI, LSI, and NSI, respectively). CONCLUSION: The 10% threshold was found to be appropriate to describe the level of expected symmetry in healthy young adults during LW, SA, and SD, however, the 10% threshold was not suitable for the STS task. Future work is needed to identify an appropriate threshold for the STS task and determine the suitability of these thresholds for different populations, varying tasks, and other kinetic and kinematic measures.