Physical Activity Variability in Patellofemoral Pain: Relationships with Clinical and Psychological Outcomes.

Objectives: To (1) compare physical activity variability between individuals with patellofemoral pain (PFP) and pain-free individuals and (2) evaluate the relationships of physical activity variability with pain severity, symptom duration, disability, and pain catastrophizing in PFP cohorts.

Design: Cross-sectional case-control study.

Setting: University research laboratory.

Participants: Individuals with PFP (N=34) and pain-free individuals (N=34) aged 18 to 40 years.

Interventions: Not applicable.

Main outcome measures: We assessed physical activity (daily steps and moderate-to-vigorous physical activity [MVPA]) over a period of 14 consecutive days using a triaxial accelerometer. Variability (coefficient of variation) for daily steps and MVPA was calculated, where higher CV values indicate greater physical activity variability. We evaluated pain severity (numeric pain rating scale), symptom duration (months), disability (Knee Injury and Osteoarthritis Outcome Score-Patellofemoral subscale), and pain catastrophizing (Pain Catastrophizing Scale). Independent t-tests or Mann-Whitney U tests evaluated group differences in physical activity variability. Spearman ρ correlation coefficients were calculated to determine the relationships of physical activity variability with pain severity, symptom duration, disability, and pain catastrophizing in PFP cohorts. Correlation coefficients were interpreted as weak (<0.40), moderate (0.40-0.70), and strong (>0.70).

Results: Age, height, and mass did not differ between individuals with PFP and pain-free individuals (P>.05). Individuals with PFP displayed greater variability in daily steps (P<.001) and MVPA (P=.001) compared to pain-free individuals. In individuals with PFP, greater variability in daily steps was moderately related to higher pain severity (ρ=0.41, P=.016), while greater variability in MVPA was weakly related to higher pain severity (ρ=0.36, P=.037).

Conclusions: Individuals with PFP demonstrated greater physical activity variability compared to pain-free individuals, which positively related to more severe pain. Future PFP research may explore the underlying factors contributing to increased physical activity variability and their potential implications for pain management.