April 14, 2026

expert reaction to an RCT on chronotype-aligned exercise timing in middle-aged adults at cardiometabolic risk

An RCT published in Open Heart looks at the timing of exercise and cardiometabolic risk in middle-aged adults. 

Dr Jeffrey Kelu, Postdoctoral Research Associate at King’s College London, said:

“This is a useful and important study because it brings personalised medicine into a very practical context by asking not only what intervention to prescribe, but also when to prescribe it.

“Exercise remains one of the most effective interventions we have for cardiometabolic disorders such as hypertension, obesity and type 2 diabetes, and these findings suggest that aligning exercise with a person’s chronotype may enhance its benefits further. Earlier studies have often suggested that afternoon or early-evening exercise is better on average, particularly for metabolic health and glucose control. What this new study adds is a more personalised perspective: rather than there being one single best time for everyone, the greatest benefit may come when exercise is aligned with an individual’s chronotype, or internal body clock.

“The study is good quality overall, with a randomised design and supervised training, but it is still moderate in size, relatively short, and limited to one population in Pakistan, so it would be valuable to see replication in larger and more diverse groups. It is also worth noting that the trial focused on sedentary middle-aged adults already at cardiometabolic risk, so it remains unclear whether the same degree of benefit would also be seen in healthier or lower-risk populations. Importantly, even the misaligned group improved, so the broader public-health message remains that any exercise is worthwhile, while timing it to biological preference may offer an additional benefit.”

Dr Nina Rzechorzek, MRC Clinician Scientist in Brain Temperature and Neural Circadian Rhythms Diplomate of the European College of Veterinary Neurology Supervisor in Physiology, University of Cambridge, said:

“This is an interesting randomised controlled trial suggesting that exercise may work better when its timing is matched to a person’s broad chronotype, rather than imposed at a non-preferred time. The study has some real strengths: participants were randomly assigned to chronotype-aligned or misaligned exercise timing, the exercise programme was supervised, and both groups undertook the same 12-week aerobic intervention, so it is a stronger design than some of the previous literature.

“However, I think the paper is stronger on exercise timing than on circadian phase measurement. The authors mainly classified participants using a morningness-eveningness questionnaire and supplemented this with short-term temperature monitoring from a skin-worn device, which is not the same as a definitive measure of internal circadian timing, despite wording that could give that impression. So, this study is best interpreted as evidence that matching exercise to broad self-reported morning or evening preference may be beneficial, rather than definitive proof that the intervention was precisely aligned to each person’s endogenous body clock.

“A further limitation is that it is not clear how far the protocol captured underlying circadian timing as opposed to socially constrained schedules, because in free-living conditions sleep and temperature rhythms are strongly influenced by work patterns, wake times and behaviour. The paper does not make clear whether participants had any unconstrained wake days or whether wake times were socially imposed, which makes it harder to know how well the protocol captured endogenous circadian timing.

“The post-intervention testing was also done only a few days after 12 weeks of timed exercise, which may reduce very acute exercise effects but does not rule out the possibility that the routine itself shifted sleep timing or circadian phase and thereby influenced outcomes such as blood pressure, heart rate variability, glucose regulation, exercise performance and sleep. That issue could have been addressed more convincingly with continuous actigraphy before, during and after the intervention, ideally including some days when wake time was unconstrained, to help distinguish biological timing from social schedule and to test whether the exercise routine itself shifted phase.

“The blood pressure effect looks potentially clinically meaningful, but the sleep findings should be interpreted more cautiously because they rely on a self-reported sleep-quality questionnaire rather than objective sleep measures, and subjective sleep quality does not always track closely with objective sleep metrics. Care should also be taken not to overinterpret the subgroup analyses, because comparisons between morning larks and night owls are described in the paper as exploratory rather than confirmatory.

“In practical terms, this does not mean exercise is currently being prescribed at the wrong clock time, or that everyone now needs formal chronotype testing. Most people who exercise routinely already do so when they prefer to or when their schedule allows, so the realistic implication is more modest: timing may be one factor worth considering when tailoring a routine that someone can sustain. The most important message remains that regular exercise matters most, but personalising timing to when someone is most likely to do it consistently may offer some added benefit. The next step would be a longer and more diverse trial with stronger circadian phenotyping and objective sleep and activity monitoring, so we can tell more clearly whether any benefit comes from true biological-clock alignment, from behaviour change, or from both.”

‘Chronotype-aligned exercise timing in middle-aged adults at cardiometabolic risk: a randomised controlled trial’ by Arsalan Tariq et al. was published in Open Heart at 23:30 hours UK time Tuesday 14th April 2026. 

DOI: 10.1136/openhrt-2025-003573

Declared interests

Dr Jeffrey Kelu: “No conflicts of interest to declare, aside from a small research grant awarded by PCR Biosystems Ltd in 2024 (£1,000).”

Dr Nina Rzechorzek: “I am an MRC Clinician Scientist based in Cambridge, with a core research focus on brain temperature dynamics and circadian rhythms. I recently completed a secondment to AstraZeneca as part of an AZ-MRC partnership. I am a Co-Founder of BioClocks UK and the Cambridge Wearables Innovation Forum, and a non-remunerated Clinical Advisor and Non-Executive Director for SomNyx Ltd. As a Trustee and research supervisor for the medical research charity APEX, I have served as Chief Investigator for several clinical studies capturing round-the-clock data from human participants, including studies involving collaborations with Empatica, Condor Instruments, BodyCap, and Dynamic Therapeutics. I am also an author on several peer-reviewed papers relating to human temperature rhythms and circadian biology.”