- The WAVE study is an on-going multicomponent comparative-effectiveness trial aimed at improving nutritional habits, increasing habitual physical activity, and preventing unhealthy changes in body composition among active 14-19 year-old adolescents. Participants were recruited through soccer teams from 13 schools and enrolled in one of two conditions: 1) a novel and combined physical space (i.e., face-to-face) and virtual space (i.e., computer-based) learning intervention (combined group), or 2) a physical space learning intervention (comparison group). All participants within a given school were allocated to the same intervention arm (combined group = 9 schools; comparison group = 4 schools). PURPOSE: To evaluate 4-month changes in step-defined physical activity between the combined and comparison groups following initiation of the WAVE study. METHODS: Step-defined physical activity was assessed using the Fitbit Zip activity monitor at baseline and 4-months following intervention implementation. Participants were instructed to wear the Fitbit around their waist during all waking hours, except during water-based activities, for 7 consecutive days. Within- and betweengroup changes in daily steps and estimated moderate-to-vigorous physical activity (MVPA; time spent ≥ 100 steps/min) were assessed using linear mixed-effects models with random effects for school and participant using the R statistical software package. RESULTS: A total of 234 adolescents (152 girls, 82 boys) provided complete data at both assessment periods. Daily steps and MVPA significantly decreased among the combined (-1,421 ± 252 steps/day, p < 0.001; -5.6 ± 1.2 min/day, respectively, p < 0.001) and comparison groups (-1,985 ± 367 steps/day, p < 0.001; - 7.2 ± 1.7 min/day, respectively, p < 0.001) from baseline to 4-months. Baseline adjusted between-group comparisons for change in steps/day (difference: 211 ± 495 steps/day, p = 0.679) and MVPA (difference: 0.9 ± 2.6 min/day, p = 0.720) were not statistically significant. CONCLUSION: Neither of the interventions evaluated increased or maintained levels of step-defined physical activity across the 4-month intervention period.