A study of 134 adults in Pakistan found that exercising at times aligned with individuals' internal body clocks led to greater improvements in blood pressure, blood sugar levels, and sleep quality than exercising at mismatched times. The research was published in the journal Open Heart.

The study included participants in their 40s and 50s, none of whom were highly fit, and all of whom had at least one cardiovascular risk factor such as high blood pressure or being overweight. Based on questionnaires, 70 participants were classified as morning larks and 64 as night owls. Some were assigned to exercise at times matching their chronotype — early risers in the morning, night owls in the evening — while others exercised at opposite times.

All participants performed supervised brisk-walking treadmill sessions for 40 minutes a day, five times a week, over three months. Those who exercised in sync with their chronotype showed larger gains in blood pressure, aerobic capacity, metabolic markers, and sleep quality compared to those on mismatched schedules.

Internal body clocks affect sleep-wake patterns and hormone and energy levels throughout the day, which can influence exercise performance and adherence. A mismatch between biological and social schedules, known as social jetlag, has been linked to increased cardiovascular risk. Night owls can be at greater risk of social jetlag and should not force early morning exercise routines.

Dr. Rajiv Sankaranarayanan of the British Cardiovascular Society said that the study findings support shifting workouts to suit body clocks and that more studies are needed to confirm this. Dr. Nina Rzechorzek, an expert in body rhythms at the University of Cambridge, said that while exercise timing may be a factor, getting enough regular exercise matters most.

The United Kingdom's National Health Service recommends strengthening activities at least two days a week and at least 75 minutes of vigorous cardiovascular exercise per week. Strength-training exercises such as wall squats or holding the plank position are among the best ways to lower blood pressure, according to verified research findings.