Researchers studied 56 highly active men and women, ages 25 to 55, for 12 weeks to help identify the most effective and feasible time of day to exercise.

During this period, participants practiced the PRISE nutrition and training program designed by Paul J Arciero, Ph.D., lead researcher, and director of the human nutrition, metabolism, and performance laboratory at Skidmore College, along with his colleagues.

The PRISE program requires participants to exercise four days a week, focusing on a different training modality each day, including resistance training, interval sprints, stretching, or endurance training.

The program also requires following a strict diet.

All participants practiced each workout for an hour or less, except for the endurance-focused workouts, which participants were allowed to practice for an hour or more. All groups completed the same type of exercise on the same day, under the direction of certified fitness professionals.

On interval sprint days and endurance days, participants practiced a sport of their choice like going on an elliptical, riding a stationary bike, roller blading, or cycling outdoors.

Participants designated to the morning group worked out between the hours of 6:30 a.m. and 8:30 a.m. and those in the evening group exercised between 6 p.m. and 8 p.m.

Though nutrition wasn’t the main focal point of this study, says Arciero, participants did follow a strict diet. Men and women in all groups met with a registered dietitian and were given a 12-week meal plan to follow.

On resistance training days, participants in all groups ate a small snack one hour before training. On stretching, endurance, and interval days, morning participants arrived fasted, but hydrated, and evening participants were also hydrated and fasted for four hours.

Morning participants were instructed to eat breakfast after workout sessions and subsequent meals in four-hour increments.

Evening participants were instructed to eat four meals a day in four-hour increments, with the last meal eaten within an hour of completing exercise. On rest days, all participants were instructed to eat breakfast within an hour of waking and following meals within those four-hour intervals. They consumed the last meal two hours before bed.

In the beginning, Arciero says, many of the participants who were active for more than four days a week were reluctant to cut back on their workouts. But that all changed once they started noticing improvements in their performance.

“They were realizing that the bottom line is all about the quality of the exercise experience, as opposed to the quantity ,” he says.

The program was inspired by the exercise recommendations of the American College of Sports Medicine.

It was designed so that people can maintain a healthy active lifestyle that works around their work and family schedules.

In the end, for women, morning exercise reduced total body and abdominal fat, decreased blood pressure, and improved lower-body muscle power, while evening exercise enhanced mood, as well as improved upper-body strength, power, and endurance.

“The likely reasons why women lose total-body and belly fat with morning exercise is because the body is in a more favorable hormonal state (lower insulin levels) which favors burning body fat as an energy source,” Aciero says.

Whereas, evening exercise is associated with building muscular strength and power because the body is in a favorable hormonal and metabolic state, he says, which contributes to improving overall mood because it acts as a “de-stressor” at the end of the day for both women and men.

Men who worked out in the both groups had improvements in mood and physical performance, and decreased both total and abdominal body fat.

But for those in the evening group, exercise had greater improvements in lowering systolic blood pressure, decreasing fatigue, and stimulating fat oxidation when compared to the morning group.

The body and heart are better prepared for the exercise later in the day than in the early morning due to certain metabolic factors in men, says Aciero. This is the reason evening exercise helps with enhancing heart health and lowering blood pressure.

The bottom line: If you’re trying to achieve a specific goal like increasing upper body strength or decreasing blood pressure, then it’s worth considering the time of day you exercise. That’s because your body may react differently to an early morning ride or strength session versus a twilight workout.

But what’s even more important to experience the effects of exercise: simply moving more, no matter what time of day that happens.