New study reveals best time of day to work out for fat loss, muscle strength

As the summer season quickly approaches, many people are looking to get into shape. But, what is the ideal time to work out? Is it best to hit the gym in the morning? Or, should you wait until the evening to pump some iron?

Well, according to new research, published Tuesday in "Frontiers in Physiology," it depends. 

In the new study, a research team led by principal investigator Paul J. Arciero had 36 women and 26 men do randomized workouts in the morning or evening for 12 weeks. 

Participants were nonsmoking, healthy, trained women and men with no known cardiovascular or metabolic diseases as assessed by a medical history and a comprehensive medical examination. In addition, all participants were highly active, middle-aged (25–55 years old) and had a lean body mass index and stable weight for at least 6 months prior to the beginning of the study.

People run on treadmills at a New York Sports Club in Brooklyn, New York (Photo by Spencer Platt/Getty Images)

The men and women were required to do multimodal workouts — a combination of physical exercises requiring different components, such as cardiorespiratory, muscular strength and flexibility — for a total of four training sessions per week.

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The people were then analyzed for their muscular strength, endurance, power, body composition, respiratory exchange ratio, behavioral mood changes and dietary intake. A total of 27 women and 20 men completed the 12-week intervention. 

In women, researchers found that both AM and PM exercise significantly reduced total body fat, along with abdominal and hip fat. However, the magnitude of improvement was significantly greater in AM exercisers for the reduction of abdominal fat and blood pressure, along with increased lower body muscle power. Meanwhile, evening exercise significantly enhanced muscular performance, which included greater gains in upper body muscle strength, power, endurance and improved mood.

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"Collectively, these findings provide support for exercise-trained women to perform a multi-model exercise training regimen (RISE) in the morning to optimize total body and abdominal fat loss, lowering of blood pressure, and increasing lower body muscular power, whereas exercise in the evening may provide improvements in upper body muscular performance, and possibly mood enhancement," the study’s authors wrote.

Meanwhile, in men, total body fat mass and abdominal and hip fat decreased for both AM and PM participants. However, evening exercise increased fat oxidation and reduced systolic blood pressure, HDL cholesterol and fatigue. 

"For exercise-trained men, multi-modal evening exercise may be more advantageous to reduce blood pressure and fatigue, as well as to maximally stimulate fat oxidation," the authors continued. "Thus, women and men respond differently to Excercise Time of Day (ETOD), and therefore, careful attention should be used in matching physical performance, cardiometabolic, and psychological mood state goals with the scheduling of multi-modal exercise training to optimize results."

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Participants also recorded their daily food and beverage consumption during the 12-week intervention. Body weight did not change in either AM or PM groups for both men and women during the study.

Limitations of this study included using only exercise-trained men and women, which suggests the results may not be applicable to less-trained or overweight men and women. The participants were also mainly Caucasian, and thus the results under-represent minority groups. In addition, the study did not focus on a midday group, and this would warrant further research.

The timing of exercise remains a controversial topic, with some experts favoring morning exercise and others favoring the evening.

According to Ben Greenfield, a bodybuilder and performance consultant, some people may be more creative and focused in the morning, and for these individuals exercise may be just a bit easier to handle from a mental standpoint.

"Regardless of whether you’re more alert mentally in the morning, the fact that your temperature tends to be lower means that the best type of exercise to do in the morning (if you’re going to exercise) is something easy and light, such as a brisk aerobic walk, an easy swim or some yoga," Greenfield wrote. 

He suggests reserving any type of intense workout — such as a weight training session or hard cardiovascular intervals — for the afternoon or evening.

Yet, other research suggests that workout results may just come down to consistency rather than a specific time of day.

In 2020, researchers from Brown Alpert Medical School looked at the exercise habits of 375 individuals who work out regularly and found that people who set the same time of day for their workouts spent notably more time working out per week than people who set random times of day for exercise.

Furthermore, they found that nearly half, 47.8%, of people who worked out at the same time of day consistently were early-morning exercisers.

The researchers concluded that "exercising at the same time of day, regardless of whether it is during the morning, afternoon, or evening, may help with achieving higher levels" of physical activity. 

You can read Arciero's book "The PRISE Life: Protein Pacing for Optimal Health and Performance" here.

FOX News contributed to this story.