Increased Duration and Intensity of Physical Activity Are Associated With Increased Pain in Individuals With Femoroacetabular Impingement Syndrome: An Ecological Momentary Assessment Study

Objective: To investigate the relation between accelerometer-measured physical activity and real-time pain in individuals with femoroacetabular impingement syndrome (FAIS). We tested the hypothesis that increased duration of high intensity activity would contribute to momentary increases in pain. Design: Observational study. Setting: Participants' natural, day-to-day environment. Participants: Population-based sample of 33 individuals with unilateral FAIS. Important eligibility criteria included no concomitant hip disorders or previous hip surgery. Key sociodemographic features include that all participants were required to have a smartphone. Interventions: Not applicable. Main outcome measures: Duration and intensity of physical activity as measured by a waist-worn accelerometer, and instantaneous pain reported in real-time smartphone-based ecological momentary assessment surveys. Physical activity variables included each person's average sedentary time, light physical activity (LPA), and moderate to vigorous physical activity (MVPA) in the 90 minutes proceeding all pain surveys as well as fluctuation in sedentary, LPA, and MVPA above or below average prior to each individual survey. Results: Linear mixed models revealed that the significant predictors of pain included fluctuation in sedentary time (B=-0.031, P<.001), average LPA (B=0.26, P=.035), and the interaction between fluctuation in LPA and fluctuation in MVPA (B=0.001, P<.001). Fluctuation in sedentary time above a person's average was associated with lower pain, while average LPA and fluctuations above average in both LPA and MVPA were associated with higher pain. Conclusions: These results suggest that individuals with FAIS can engage in health-enhancing MVPA but should focus on avoiding concurrent increase above average in both high intensity and LPA in the same 90-minute period. Future work is warranted testing the efficacy of such an approach on pain. Additionally, given that high levels of LPA may arise from a host of socioeconomic factors, additional research is needed to disentangle the effect of LPA on pain in FAIS.