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A Comparison Of Lower Extremity Joint Kinetics During Walking Between Runners And Inactive Individuals.

Physical activity (PA) levels and intensity can mitigate age related distal to proximal shift in muscle function. So far, PA was recorded via surveys and dichotomized when assessing its relationship to gait adaptations. Prospectively recorded PA quantified continuously and categorically may provide information on gait adaptations occurring along the PA continuum. PURPOSE: Determine the relationship between ankle, knee, and hip joint kinetics and weekly moderate to vigorous physical activity (MVPA) minutes among active adults. METHODS: A 3D overground running gait analysis was performed on 44 active adults (18-65 years). Joint work ratios (ankle:hip, ankle:knee, knee:hip) and %contribution of each joint to total lower limb positive and negative work were calculated (outcomes). Subjects wore a wrist-worn PA tracker for 2 weeks. The total minutes performing MVPA (exposure) was averaged over 2 weeks. MVPA was analyzed continuously and categorically into tertiles (1-low, 2-moderate, 3-high). Multiple linear regression models (α<0.05, covariates = age, sex) assessed the relationship of each outcome to weekly MVPA, both continuous and tertiles. RESULTS: Gait differences between MVPA tertiles 1 and 3 were not significant (p>0.05). Compared with tertile 1, subjects in MVPA tertile 2 displayed 26.30% decreased ankle:knee positive work (p=0.009, CI: 0.58-0.92), 9.29% decreased ankle contribution to total positive work (p=0.011, CI: 0.84-0.97), and 23.07% increased knee contribution to total positive work (p=0.014, CI: 0.84-0.97). CONCLUSION: Our results indicate amplified biomechanical plasticity from the ankle to knee with increased weekly MVPA. Consistent with previous research (Malero et al., JAB, 2020), this unexpected trend may be due to increased muscle capacity at the knee but not ankle with greater PA exposure. The relationship of weekly MVPA to gait plasticity appears to be non-linear, as tertile 1 displayed similar kinetics to tertile 3 but not 2. Given that gait interventions targeting ankle propulsive power successfully attenuated plasticity (Fickey et al., JEB, 2018), it may be that tertile 2 performed PA which demanded less from ankle musculature thereby blunting ankle kinetic adaptations. Thus, MVPA composition in addition to weekly minutes may influence plasticity. Age-related changes affecting gait can begin as early as the third decade. Running requires greater plantarflexor involvement than walking, suggesting that running may provide a large enough benefit in retaining the plantar flexor function. In doing so, running may reduce or postpone the distal-to-proximal shift in joint kinetics that has been observed in aging individuals. PURPOSE: The purpose of this study was to investigate walking mechanics and the presence of age-related gait adaptations in runners between the ages of 36-45 years old compared to inactive individuals of the same age. METHODS: A total of 30 individuals aged 36-45 years old were included in this analysis (Table 1). Participants walked at a self-selected pace over a 17-m long runway with force platforms collecting kinetic data. Six successful walking trials were selected for analysis. Between-group differences were determined using independent t-tests and effect sizes. RESULTS: Mean values for kinetic variables of interest are shown in Table 2. When normalized to body mass (BM), runners generated greater knee power than inactive individuals (p = 0.01). When normalized to fat-free mass (FFM), inactive individuals had a greater peak plantarflexor moment than runners (p = 0.01). CONCLUSION: Knee power was no longer greater in runners than inactive individuals when normalized to FFM,