Linking vertical ground reaction force loading rates and physical activity levels in individuals with and without...

Individuals with patellofemoral pain (PFP) may walk with higher vertical ground reaction force loading rates (vGRF-LR) compared to pain-free controls, which could relate to modified physical activity behaviors. However, their relationships have not been studied in the PFP literature. This study aimed to explore the association between walking vGRF-LR and physical activity levels in individuals with PFP and pain-free controls and to compare vGRF-LR between groups. Twenty participants (10 with PFP and 10 pain-free) participated in this cross-sectional study. Participants wore a triaxial accelerometer for seven consecutive days to measure physical activity levels (daily steps and time spent in moderate-to-vigorous physical activity [MVPA]). Participants also completed a biomechanical assessment while walking at 1.25 m/s on a force plate-embedded treadmill. vGRF-LR were calculated as the average loading rate of 20-80 % and at 60 % of the stance phase. t vGRF-LR were not associated with daily steps and time spent in MVPA in either the PFP (0.15 ≤ r ≤ 0.26; p > 0.05) or pain-free (-0.37 ≤ r ≤ -0.08; p > 0.05) group. However, individuals with PFP walked with higher vGRF-LR averaged between 20-80 % of the stance phase (p = 0.037; d = 1.04) and peak vGRF-LR at 60 % of the stance phase (p = 0.042; d = 1.02) compared to pain-free controls. Our findings suggest that walking loading rates are not associated with physical activity levels in either group, despite higher loading rates in PFP cohorts. Given the lack of associations between these variables, future studies should examine other potential factors that may enhance our understanding of loading rates or physical activity in individuals with or without PFP.