BACKGROUND CONTEXT Walking at least 4,500 steps/day or engaging in at least 60 minutes of moderate-to-vigorous physical activity/week are known to provide multiple health benefits and prevent disability in adults with and without musculoskeletal pain. However, little is known about the impact of physical activity on outcomes following spine surgery. PURPOSE The primary objective of this study was to determine whether early postoperative physical activity is associated with clinically meaningful improvement in disability in patients undergoing spine surgery. A secondary objective was to investigate the physical activity threshold that best discriminates improvement in disability at one year following spine surgery. STUDY DESIGN/SETTING Secondary analysis of randomized controlled trial data. PATIENT SAMPLE A total of 248 participants undergoing elective surgery for a degenerative lumbar spine condition. OUTCOME MEASURES Clinically meaningful improvement in disability was considered a 30% reduction in Oswestry Disability Index (ODI) scores from baseline (6 weeks after surgery) to 1-year follow-up. METHODS Physical activity was measured using an accelerometer (Actigraph GT3X) worn for at least 10 hours/day for at least 3 days at 6-weeks following spine surgery. Physical activity was quantified as steps/day and time spent in moderate-to-vigorous physical activity (ie, at least 2,020 counts/minute). Multivariable logistic regression analysis was conducted to determine the association between steps/day at 6 weeks and clinically meaningful improvement in disability at 1 year, controlling for age, body mass index (BMI), education, race, sex, previous surgery, spinal procedure, baseline ODI score, and back and leg pain. Receiver operating characteristic curves were used to identify steps/day and moderate-to-vigorous physical activity/week that best discriminated the likelihood of achieving clinical improvement. RESULTS Of 248 participants, 216 participants (mean [SD]; age= 63[11] years, BMI= 32[7] kg/m2, 52% female) had physical activity for at least 3 valid days. Of 216 patients, 43% (n=93) achieved clinical improvement in ODI at 1-year following spine surgery. Each additional 1000 steps/day and additional 1 minute of moderate-to-vigorous physical activity/day were associated with 27% (OR=1.27, 95% CI=1.07, 1.51) and 4% (OR=1.04, 95% CI=1.01, 1.08) higher odds of achieving clinically meaningful improvement in ODI, respectively. At 6 weeks following spine surgery, walking less than 3000 steps/day (sensitivity = 68%, specificity = 52%) was associated with 66% (OR=0.34, 95% CI=0.16, 0.69) lower odds of achieving clinical improvement in disability compared to those who walked at least 3000 steps/day. In addition, engaging in less than 21 minutes of moderate-to-vigorous physical activity/week (sensitivity = 62%, specificity = 48%) was associated with a 46% (OR=0.54, 95% CI=0.29, 1.02) lower odds of achieving clinical improvement in disability at 1-year postoperative compared to those who engaged in at least 21 minutes of moderate-to-vigorous physical activity/week. CONCLUSIONS Walking at least 3,000 steps/day or engaging in at least 21 minutes of moderate-to-vigorous physical activity/week may serve as an initial recommendation for patients early after spine surgery. Results suggest that these early postoperative thresholds may optimize clinical improvement in disability at 1 year following spine surgery. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.