IMPORTANCE: The efficacy of physical activity interventions among individuals with type 2 diabetes has been established; however, practical approaches to translate and extend these findings into community settings have not been well explored. OBJECTIVE: To test the effectiveness of providing varying frequencies of weekly structured exercise sessions to improve diabetes control. DESIGN, SETTING, AND PARTICIPANTS: The IMPACT (Initiate and Maintain Physical Activity in Communities Trial) study was a controlled randomized clinical trial (randomization occurred from October 2016 to April 2019) that included a 6-month, structured exercise intervention either once or thrice weekly versus usual care (UC; advice only). The exercise intervention was conducted at community-based fitness centers. Follow-up visits were conducted in a university research clinic. Participants included adults with type 2 diabetes (hemoglobin A1c (HbA1c) 6.5% to 13.0%, not taking insulin, and no precluding health issues). Data analysis was performed from January to April 2022. INTERVENTIONS: A once-weekly structured exercise group, a thrice-weekly structured exercise group, or UC. MAIN OUTCOMES AND MEASURES: The primary outcome was HbA1c at 6 months. RESULTS: A total of 357 participants (143 women (40.1%)) with a mean (SD) age of 57.4 (11.1) years were randomized (119 each to the UC, once-weekly exercise, and thrice-weekly exercise groups). There was no significant difference in HbA1c change by study group in the intention-to-treat analysis at 6 months. Specifically, HbA1c changed by -0.23% (95% CI -0.48% to 0.01%) in the thrice-weekly exercise group and by -0.16% (95% CI -0.41% to 0.09%) in the once-weekly exercise group. A total of 62 participants (52.1%) in the once-weekly exercise group and 56 participants (47.1%) in the thrice-weekly exercise group were at least 50% adherent to the assigned structured exercise regimen and were included in the per-protocol analysis. Per-protocol analysis showed that HbA1c changed by -0.35% (95% CI -0.60% to -0.10%; p = 0.005) at 3 months and by -0.38% (95% CI -0.65% to -0.12%; p = 0.005) at 6 months in the thrice-weekly exercise group compared with UC. There was no significant decrease in HbA1c in the once-weekly exercise group. The exercise intervention was effective in improving self-reported minutes of metabolic equivalent tasks per week for participants in the thrice-weekly exercise group (both overall and per protocol). CONCLUSIONS AND RELEVANCE: Although the intervention was not effective in the intention-to-treat analysis, participants in the thrice-weekly exercise group who attended at least 50% of the sessions during the 6-month exercise intervention program improved HbA1c levels at 6 months. Future efforts should focus on improving adherence to thrice-weekly structured exercise programs to meet exercise guidelines. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT02061579.

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