Background/Purpose: Following knee replacement surgery, adults report improvements in function and pain, but physical activity (PA) often remains unchanged. Exercise identity, the degree to which one views themselves as an exerciser, may influence individual’s PA levels. Therefore, the purpose of this study was to determine if participants’ exercise identity at the start of outpatient physical therapy (PT) predicted their objectively measured PA at 12 weeks post-op.

Methods: Adults with knee replacement were recruited at their first outpatient PT appointment (31.9±9.5 days after surgery) and randomized to a 12-week PA intervention (control group vs. enhanced PA intervention group). At baseline, participants completed a self-reported exercise identity survey and at both baseline and the 12-week follow-up assessment, they wore an ActiGraph accelerometer for 7 days. The ActiGraph monitor assessed light PA (LPA) (100-2019 cpm), moderate-to-vigorous PA (MVPA) ( >2020 cpm), and steps. Only participants with valid wear time (> 10 hours for at least 4 days) were included in analyses, and total activity was divided by valid days of wear time to get daily averages of each type of activity for each participant. The self-reported exercise identity survey (Wilson & Muon, 2008) consisted of 9 items to rate adults’ feelings about exercise on a 5-Point Likert scale from Strongly Disagree to Strongly Agree. The 9 items were summed to get a total exercise identity score (0-36). A general linear model was used to examine the prediction of baseline exercise identity score on 12-week follow-up objectively measured LPA, MVPA, and steps. Analyses controlled for age, sex, and race in addition to intervention group, days from surgery and baseline PA.

Results: Of the 45 randomized participants, 35 completed the intervention and had complete exercise identity and ActiGraph activity data. Participants were 65.5±7.5 years old, 57.1% female, 100% non-Hispanic or Latino, 74.3% white, with a BMI of 32.2±6.7 kg/m². At the 12-week assessment, participants had an average of 4122.1±2162.6 steps/day and spent 231.3±77.1 mins/day in LPA and 8.7±9.4 mins/day in MVPA. Results indicate that high self-identity was a significant predictor of MVPA at 12 weeks (b=0.438, p=0.047), but did not significantly predict LPA (b=3.021, p=0.120) or steps (b=94.455, p=0.076). Results also indicate that MVPA at 12-week post-op can be predicted by age (b=-0.578, p=0.011) and sex (b=8.751, p=0.039).

Conclusion: Exercise identity at the start of outpatient PT predicted MVPA but not LPA or steps at 12-weeks post-op. These results suggest that the self-report exercise identity survey could be a proxy for MVPA, however, may not be appropriate to predict lifestyle activity (LPA and steps). Utilizing this tool at the onset of outpatient PT could help physical therapists identify those who may struggle to increase activity. Additional emphasis could be placed on identifying activities that adults would enjoy in addition to setting PA goals and problem-solving barriers.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/exercise-identity-at-the-start-of-outpatient-physical-therapy-prospectively-predicts-physical-activity-at-12-weeks-after-total-knee-replacement/