The trial enrolled 66 adults aged 60 to 75 with type 2 diabetes who had not been meeting recommended physical activity levels. Participants were randomly assigned in equal numbers to a morning exercise group, an evening exercise group, or a control group. Both exercise groups completed 12 weeks of moderate-intensity combined aerobic and resistance training delivered online three times per week, with the morning group training from 9:00 to 10:10 and the evening group from 19:00 to 20:10. The control group maintained usual lifestyle habits and attended weekly health education sessions without structured exercise. Fifty-eight participants completed the trial and were included in the final analysis.

The researchers measured four complementary indicators of vascular health: flow-mediated vasodilation, or FMD, which gauges how well the brachial artery expands in response to increased blood flow; brachial-ankle pulse wave velocity, or baPWV, the standard clinical marker of arterial stiffness; brachial blood pressure; and circulating plasma nitric oxide, the key vasodilator molecule produced by endothelial cells. Assessments were performed at baseline and after the intervention, with post-intervention testing conducted 48 to 72 hours after the final session to eliminate acute exercise effects, and always at the same time of day to control for circadian confounding.

The results showed that both exercise groups improved. FMD increased significantly from baseline in the morning group, rising from about 5.0 to 6.3 percent, and in the evening group, rising from about 5.5 to 7.2 percent, while systolic blood pressure and mean arterial pressure fell in both. Arterial stiffness also declined in both groups, but the magnitude differed strikingly: baPWV dropped by an average of 89.2 centimetres per second in the morning group and by 221.1 centimetres per second in the evening group. An exploratory analysis directly comparing the two exercise groups found a statistically significant interaction for baPWV, indicating a greater reduction with evening exercise.

Nitric oxide told a similar story. Plasma NO levels, measured indirectly through its metabolites nitrite and nitrate, increased significantly only in the evening group, from 31.75 to 46.30 micromoles per litre, whereas the morning group showed essentially no change. Post-intervention, the evening group exhibited higher FMD and NO levels and lower mean arterial pressure than the control group. The exploratory comparison of the two exercise groups for NO showed a numerically greater increase with evening exercise, although the interaction just missed statistical significance at p = 0.051.

Why might the clock matter? The answer lies in circadian physiology. In the early morning, sympathetic nervous system activity surges, accompanied by elevated cortisol, catecholamines, angiotensin II, platelet aggregates, and plasminogen activator inhibitor-1. Heart rate and blood pressure rise, serum nitric oxide falls, and brachial artery FMD is attenuated compared with other times of day. These alterations are thought to underlie the well-documented morning peak of cardiovascular events. By contrast, in the early evening most of these patterns reverse, creating a vascular environment with lower sympathetic tone and greater vasodilatory capacity, which may allow exercise-induced shear stress on endothelial cells to translate more effectively into nitric oxide synthesis and arterial adaptations.

The nitric oxide pathway is central to the trial’s mechanistic logic. Exercise increases blood flow and shear stress on the endothelium, which promotes endothelial nitric oxide synthase phosphorylation and NO production while reducing oxidative stress and proinflammatory signalling. NO, in turn, modulates vascular tone and arterial elasticity, so a larger training-induced NO response could plausibly contribute to the greater reduction in arterial stiffness observed after evening sessions. The authors note that plasma NO and FMD provide complementary biochemical and functional perspectives on vascular adaptation, and that considerable inter-individual variability in NO responses may reflect heterogeneity in vascular status within this population.

The trial has notable strengths. It is, to the researchers’ knowledge, the first randomised controlled trial to compare the long-term effects of morning versus evening combined aerobic and resistance exercise on endothelial function, arterial stiffness, and blood pressure in older adults with type 2 diabetes. Attendance was high in both exercise groups, at 95.3 percent in the morning and 97.5 percent in the evening, no exercise-related adverse events occurred, and outcome assessors and data analysts were blinded to group allocation. The consistent timing of vascular assessments before and after the intervention minimised the confounding influence of circadian variation on the outcome measures, a limitation that plagues many acute time-of-day studies.

Limitations temper the conclusions. The study did not include an afternoon exercise group, so whether midday sessions confer different vascular benefits remains unknown. Baseline use of lipid-lowering medication differed significantly among the three groups, an imbalance that likely arose by chance but may have influenced between-group vascular responses. Dietary intake was not strictly controlled, and sleep, physical activity outside prescribed sessions, and medication timing were not monitored during the intervention. Shear rate was not assessed during FMD measurement because the ultrasound system could not record brachial artery diameter and blood velocity simultaneously after cuff deflation. The authors call for future studies to monitor these variables and to include longer follow-up to determine whether the observed adaptations are sustained.

Even so, the findings carry practical weight. FMD is an independent predictor of future cardiovascular events, and evidence suggests that a 1 percent increase in FMD is associated with roughly a 13 percent reduction in cardiovascular risk. In this trial, FMD increased by an average of 1.45 percent across the two exercise groups, indicating potentially clinically relevant improvements in endothelial function. Current exercise guidelines for people with type 2 diabetes specify the type, intensity, frequency, duration, and progression of exercise but offer no clear guidance on timing within the day. This trial suggests that evening exercise may provide additional vascular benefits, particularly for arterial stiffness, and that exercise timing deserves consideration in exercise planning for this population. The study was registered in the Chinese Clinical Trial Registry under identifier ChiCTR2300073737.

Subject of Research: Exercise timing and vascular health in type 2 diabetes

Article Title: Effects of morning versus evening exercise on vascular function in older adults with type 2 diabetes: a randomised controlled trial

Article References: Ma, Z., Lin, Y., Zhu, Z., & Cao, Z.-B. (2026). Effects of morning versus evening exercise on vascular function in older adults with type 2 diabetes: a randomised controlled trial. Frontiers in Endocrinology, 17, Article 1976870. https://doi.org/10.3389/fendo.2026.1976870

Image Credits: AI Generated

DOI: 10.3389/fendo.2026.1976870

Keywords: type 2 diabetes, exercise timing, vascular function, arterial stiffness, nitric oxide, randomised controlled trial, circadian rhythm, cardiovascular risk, Effects, morning, versus, evening