Benefits of Exercise Vary by Time of Day, Gender, Study Finds

Women burn more belly fat and reduce their blood pressure more when exercising in the morning while they increase their muscular performance when they exercise at night, according to a study published May 31 in the Frontiers in Physiology.

On the other hand, men increase fat oxidation and reduce their systolic blood pressure and fatigue when they exercise at night.

A 12-week study conducted in the United States split already-active participants into two groups—one that exercised for an hour before 8:30 a.m. and the other that exercised between 6 p.m. and 8 p.m. Both groups participated in the same activities (resistance training, interval sprints, stretching/yoga/Pilates, and endurance training) and followed a designed meal plan.

The study involved just 30 women and 26 men between the ages of 25 and 55, but only 27 women and 20 men completed the study.

Results showed that every participant improved their overall health and performance in the areas tested during the study, regardless of when they exercised. Areas measured were muscular strength, endurance and power, body composition, blood pressure, respiratory exchange ratio, profile of mood states and dietary intake.

For women, both the morning and evening exercise groups “significantly” reduced total body fat, abdominal and hip fat, and increased fat-free mass during the study. However, the improvement in total body fat mass and abdominal fat percentage was “significantly” greater in the morning exercisers.  

For the male participants, total body fat mass and body fat, abdominal and hip fat decreased, and fat-free mass increased “significantly” in both groups with no differences between groups.

The study also measured performance changes, and again, the male participants showed no difference between the morning and evening groups for any of the performance outcomes. However, for women, those who exercised in the evening had greater improvement in upper body muscle function while women in the morning exercise group showed greater improvement on lower body peak power.

The impact on cardiometabolic outcomes showed that total cholesterol, systolic and diastolic blood pressure, aortic and brachial augmentation index decreased “significantly” in both groups of women, but the women who exercised in the morning reduced their systolic and diastolic blood pressure to a greater degree than evening exercisers.

The men who exercised in the morning had no changes to their cardiometabolic variables, and the total cholesterol, systolic blood pressure and respiratory exchange ratio declined “significantly” for men who exercised in the evening compared to morning exercisers.