Synching workouts to natural body clock may help maximize heart health benefits

This randomized controlled clinical trial enrolled 150 participants, of whom 134 completed the study. Participants were adults in Lahore, Pakistan, between the ages of 40-60 years.

All participants were sedentary and had at least one risk factor for cardiovascular disease. These included factors like blood pressure within a certain range or having a family history of premature cardiovascular disease. However, they excluded individuals who already had certain confirmed conditions, like coronary artery disease, as well as those taking certain medications.

Researchers considered participants’ chronotypes, which are their natural tendencies toward being a morning or an evening person. They explain that “individuals differ not only in their preferred sleep and wake times but also in the timing of optimal physical performance and cardiovascular response to exercise.” They used a questionnaire to determine each participant’s chronotype, which was then confirmed by evaluating body temperature.

Next, participants underwent the exercise intervention for 12 weeks. Participants did moderate-intensity aerobic training sessions. These included using a treadmill or walking briskly for 30 minutes and 5-minute warm-ups and cool-downs. Participants did these sessions at the University of Lahore teaching hospital, five days a week.

Participants performed the exercise intervention within a certain range in the morning or evening. Some participants performed exercise interventions in line with their chronotype, while others exercised at the opposite time, such as a morning person exercising in the evening, as assigned in their group.

Researchers measured participants’ blood pressure, heart rate variability, peak oxygen consumption, sleep quality, fasting blood sugar, and “bad” cholesterol levels at baseline and then again after the exercise intervention ended.

The group that exercised at a time that aligned with their natural rhythms, such as morning or evening types, had better outcomes for blood pressure and heart rate variability. They also appeared to have better performance and exercise capacity outcomes. Finally, they also had better cholesterol, fasting glucose, and sleep quality outcomes.

The observed improvements were better for the aligned group when it came to all outcomes. For example, the aligned group saw systolic blood pressure drop by almost 11 mmHg while the misaligned group only saw a 5.5 mmHg decrease. Similarly, “bad” cholesterol levels dropped by 13.7 mg/dL in the aligned group and only by 7.6 mg/dL in the misaligned group.

Additional analysis found that participants who already had high blood pressure at baseline saw the greatest reduction in blood pressure when exercise was chronotype-aligned.

They also found that chronotype-aligned exercise was the greatest independent predictor of change in systolic blood pressure, suggesting that this exercise timing consideration could be particularly helpful for blood pressure.

Cheng-Han Chen, MD, board certified interventional cardiologist and medical director of the Structural Heart Program at MemorialCare Saddleback Medical Center in Laguna Hills, CA, who was not involved in the study, commented the following:

“This study characterized individuals by their chronotype (whether they were ‘early birds’ or ‘night owls’), and found that the participants [who] were assigned to exercise during their ‘preferred’ time actually underwent greater improvements to various cardiometabolic factors (such as blood pressure, cholesterol, and glucose values) compared to those exercising at ‘non-preferred’ times.”

“These results add to our understanding of how aligning exercise with someone’s internal circadian clock can potentially improve health outcomes and suggest a strategy to help us optimize the beneficial effects of exercise.”
— Cheng-Han Chen, MD

The researchers also found that morning-type participants in both aligned and misaligned groups saw better improvement than evening-type participants.

They explained that “the magnitude of improvement appeared descriptively greater in morning-type participants for several cardiovascular, autonomic and fitness-related measures.” However, the authors note that this data gives speculative insights.

This study was fairly small, and the exercise intervention lasted for a fairly short time. Researchers note that it “does not provide insight into long-term outcomes or sustainability.”

It also focused on a specific population already at risk of cardiovascular disease. The authors note that this data was from government hospitals in Lahore and that most participants had “middle- or lower- income backgrounds.” Additionally, they chose to exclude individuals with intermediate chronotypes, so those who didn’t quite fit into the morning or evening types.

Thus, it’s unclear whether the results would be the same in other groups, such as those not at risk for cardiovascular disease, and the generalizability is limited.

Full blinding in this type of study wasn’t possible either, so there is some risk of bias. Adherence to the exercise intervention was also higher in the aligned group. Participant dropout also could have affected the results. It’s also possible that participants’ evaluations of themselves as morning or evening types were inaccurate. Exercise adherence partially relied on participant reporting, which could also be inaccurate. Assessment of sleep quality also relied on participant reporting.

Researchers chose to estimate peak oxygen consumption, which may not be as precise. Finally, researchers note that although they included only participants on stable medications, it’s still possible that these medications influenced the outcomes.

The specific reasons for the observed results could be an aspect of future research.

Danielle El Haddad, MD, cardiovascular medicine, UTMB, who was also not involved in the study, noted the following:

“Several limitations should be considered when interpreting these findings. The study population was small and demographically restricted to middle-aged individuals (40–60 years) from a low- to middle-income Pakistani cohort, limiting external validity.”

“In addition, the exclusion of patients receiving commonly prescribed cardiovascular medications—specifically beta blockers and calcium channel blockers—reduces applicability to routine clinical practice, where such therapies are prevalent. The lack of blinding further introduces the potential for bias, particularly in subjective or effort-dependent outcomes such as exercise performance and adherence,” El Haddad added.

The research suggests a simple way to improve blood pressure and other outcomes through a more individualized approach, though more research is required.

Afaq Motiwala, MD, assistant professor for interventional cardiology at the University of Texas Medical Branch, who was also not involved in the study, noted the following to Medical News Today:

“This study supports a shift toward personalized lifestyle medicine, where exercise recommendations consider not only type, intensity, and frequency, but also timing of exercise. Aligning exercise with an individual’s circadian biology may maximize its clinical benefits, and also improve adherence, as patients are more likely to maintain routines that fit their natural energy patterns.”

People can discuss their options for exercise programs with their doctors, as well as how timing may impact outcomes.

It’s important to note that even in this study, both groups saw benefits. Exercise is still important overall, regardless of getting the timing perfect.

“We know that any exercise is better than none. We are just beginning to learn how the timing of exercise during the day can make it even more effective,” Chen said.