Morning versus evening aerobic exercise and atherogenic and fat-distribution indices in older women with type 2 diabetes: a quasi-experimental controlled study

Purpose To compare the effects of 12 weeks of morning versus evening aerobic exercise on fat-distribution, insulin-resistance and atherogenic indices in older women with type 2 diabetes mellitus (T2DM). Methods In this quasi-experimental controlled study, 45 sedentary postmenopausal women with T2DM aged 60–65 years were allocated by availability to supervised moderate-intensity aerobic training in the morning (09:00 h) or evening (21:00 h), three sessions per week for 12 weeks, or to a non-exercising control group. Thirteen anthropometric and biochemical indices were assessed before and after the intervention. Between-group differences were analysed by baseline-adjusted ANCOVA with false-discovery-rate control and confirmed by linear mixed-effects, change-score and non-parametric analyses. Results Forty-two women (14 per group) completed the study. Significant group effects were found for insulin resistance (HOMA-IR), abdominal volume index, body adiposity index (BAI), waist-to-height ratio, visceral adiposity index (VAI), triglyceride–glucose index (TyG), TyG–waist circumference (TyG–WC), TyG–body mass index, atherogenic index of plasma (AIP) and Castelli’s risk indices I and II (CRI-I, CRI-II) (all p < 0.001; q < 0.001). These indices improved in both exercise groups and mostly deteriorated in controls. Evening exercise was superior to morning exercise for BAI, VAI, AIP, CRI-I and CRI-II (p = 0.044 to p < 0.001), and change-score analysis additionally favoured evening exercise for TyG and TyG–WC. Conclusion Aerobic exercise improved adiposity, insulin-resistance and atherogenic indices in older women with T2DM, with greater benefit from evening sessions for lipid-related and visceral-fat indices. Randomised trials are needed to confirm this timing effect. Trial registration Iranian Registry of Clinical Trials, IRCT20181212041935N1; registered 18 February 2024.