Morning or Evening Workouts? Study Says No Clear Winner for Women With Obesity

Women in both exercise groups could lift more weight by the end of the program, with improvements appearing during morning and evening testing rather than being confined to their usual workout hours.

Finding room for exercise can mean squeezing a workout in before breakfast or heading to the gym after a busy day. A new study offers some reassurance that either schedule can deliver benefits. The research, titled 'Morning or evening? Time of day does not affect body composition, cardiopulmonary performance, and muscle strength responses to combined training in women with obesity,' was published in Frontiers in Sports and Active Living.

Researchers in Brazil found that eight weeks of strength and aerobic training improved muscle strength and selected fitness measures in previously untrained women with obesity, with no consistent advantage for morning or evening sessions. Changes in weight, body fat, blood pressure, and heart rate were limited, showing that better physical performance can develop without a noticeable change on the scales.

What the Women Did During the Eight-Week Program

The trial enrolled women aged 18–50 who had not taken part in structured exercise for at least three months and met the study's obesity criteria, including elevated body fat and a waist circumference of at least 88 centimetres. The final analysis included 49 women; 17 trained between 7 a.m. and 10 a.m., 19 exercised between 6 p.m. and 9 p.m., and 13 formed a control group that completed the assessments without joining the exercise program.

Both exercise groups followed the same supervised routine three times a week, completing a mix of resistance exercises and treadmill exercise over 24 planned sessions. Workouts grew from 40 to 60 minutes, with equal time devoted to each type of activity and gradual increases in difficulty.

Resistance exercises included bench presses, leg presses, seated rows, leg curls, lateral raises, and knee extensions, with participants progressing toward heavier loads and fewer repetitions. Treadmill exercise increased from 20 to 30 minutes at intensities tailored to each woman's measured fitness.

Participants were asked to keep their usual eating, sleeping, and lifestyle habits, with no prescribed weight-loss diet. Researchers assessed body composition before and after training and tested strength, exercise performance, blood pressure, and heart rate in both the morning and evening, allowing them to separate training schedules from testing times.

Strength Gains Were the Clearest Result

Women in both exercise groups could lift more weight by the end of the program, with improvements appearing during morning and evening testing rather than being confined to their usual workout hours. Bench-press strength increased by roughly 5–6 kilograms in the morning group and about 5–5.5 kilograms in the evening group. These measurements represented the heaviest load participants could lift once, and both exercise groups improved significantly more than the control group.

Leg-press gains ranged from about 22–29 kilograms in the morning group and 17–18 kilograms in the evening group, depending on testing time. Only the morning group's overall improvement was statistically greater than the control group's, and the direct comparison between the two training schedules did not show any difference.

Aerobic fitness showed a more mixed pattern; Peak oxygen uptake, known as VO₂peak, measures the highest rate of oxygen use reached during an exercise test and gives researchers an indication of cardiorespiratory fitness.

The morning group's VO₂peak increased by 2.42 millilitres per kilogram per minute during morning testing; the evening group improved by 1.57 millilitres per kilogram per minute during evening testing. Averaging the testing times showed a clear advantage over the control group only for morning training, without a significant difference between morning and evening training.

Treadmill speed and time spent completing the exercise test increased over the study period, though changes did not differ significantly among the groups. The pattern offers no firm evidence that matching workout and testing times produces better adaptations.

Better Fitness Did Not Mean Weight Loss

Eight weeks of exercise produced no changes in body weight, BMI, body fat, or muscle mass, regardless of when participants trained. The strength improvements came without measurable muscle growth, a useful reminder that these outcomes do not necessarily move together.

Waist circumference increased by around three centimetres in the control group and remained broadly stable in the exercise groups. Differences in waist changes among groups were not significant, so the result does not establish that exercise prevented waist gain; the researchers noted that normal biological variation could explain the control group's increase.

The authors suggested that the short program, its overall exercise dose, and the absence of dietary energy restriction may help explain the limited body-composition changes. Those possibilities were not tested directly, and the findings cannot tell readers which workout time would work best for fat loss during a different program.

Blood pressure and heart rate showed no consistent lasting improvements linked to either schedule. Participants generally began with normal cardiovascular values, leaving less room for measurable improvement, and blood-pressure readings taken immediately after demanding exercise were more variable than resting measurements.

A Useful Finding With Real-Life Limits

Daily biological rhythms gave researchers a reason to suspect that workout timing might influence results, and their expectation that evening exercise would produce greater benefits was not supported.

The small final sample, eight-week duration, lack of long-term follow-up, and incomplete blinding limit how confidently the results can be applied elsewhere. No final participants reported an evening preference, preventing a meaningful comparison of natural early risers and night owls. Diet, sleep, and everyday activity were monitored but not included in the main analyses, and biological markers of circadian rhythms were not measured.

For previously untrained women with obesity, the study supports choosing a morning or evening schedule that fits daily life, with both offering opportunities to build strength and improve selected fitness measures. It found no clear winner between those schedules; it did not prove that timing is irrelevant for every person, health outcome, or training program.