Purpose: Lower knee joint loading during walking is associated with markers of adverse cartilage health after anterior cruciate ligament reconstruction (ACLR), suggesting that underloading may play a role in the development of post-traumatic osteoarthritis. However, these magnitude-based measures of loading were determined using laboratory-based gait analyses over a single step, which may not reflect habitual daily walking. Understanding the characteristics of daily walking in individuals after ACLR is a critical first step toward understanding how daily walking affects cartilage health in this population. Thus, the purpose of this preliminary analysis was to examine differences in volume and intensity characteristics of daily walking between individuals early after ACLR, later after ACLR, and uninjured controls. Methods: This cross-sectional study is a secondary analysis of data from three prior studies. We included individuals who were at least 6 months post-ACLR, and divided the sample based on time since ACLR: early (6-12 months post-ACLR; 8.0 ± 1.5 months post-ACLR) and later (>12 months post-ACLR; 61.4 ± 41.9 months post-ACLR). We included individuals without a history of lower extremity injury or surgery as a control group. Daily walking was assessed using a triaxial accelerometer (Actigraph Link) worn at the right hip. Participants were instructed to wear the accelerometer during all waking hours aside from water activities for 7 days. Data were considered valid if the accelerometers was worn for ≥ 10 hours/day for ≥ 4 days. The outcome of interest was daily walking volume (total steps per day), daily walking intensity (steps per day at a moderate-vigorous (MV) intensity), and proportion of total steps accumulated at MV (steps per day at MV/total steps per day expressed as a percentage). MV intensity was defined as walking at ≥ 100 steps per minute. For this preliminary analysis, we calculated effect sizes (Cohen’s d) to evaluate the difference in daily walking between groups (early, late, control). Effect size magnitude was interpreted as no effect (0-0.19), small (0.20-0.49), medium (0.50-0.79) and large (≥0.8). Results: Sixty-two participants (22.5 ± 4.1 years, 48% men, body mass index 24.2 ± 2.8 kg/m2) were included in this analysis (early n=21, later n=19, control n=22; Table 1). Compared to the later group post-ACLR, the early group accumulated fewer total steps per day (large effect, Table 2), fewer steps at MV (medium effect), and a lower proportion of steps at MV (small effect). Compared to the control group, the early group accumulated similar total steps per day, yet fewer steps at MV (small effect) and a lower proportion of steps at MV (medium effect). Compared to the control group, the later group accumulated more total steps per day (medium effect), yet similar steps at MV and a lower proportion of steps at MV (small effect).View Large Image Figure ViewerDownload Hi-res image Download (PPT) Conclusions: This preliminary analysis suggests that individuals early after ACLR accumulate fewer total steps per day and fewer steps at MV compared to individuals late after ACLR and fewer steps at MV compared to healthy controls. Interestingly, individuals late after ACLR accumulate a lower proportion of daily steps at MV compared to healthy peers, despite walking more total steps. This analysis was limited to description of effect sizes due to small sample sizes and should be interpreted accordingly. Further studies in larger samples are warranted to understand daily walking recovery after ACLR and the extent to which it relates to measures of joint health.