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The time of day people choose to exercise could have different effects. David Trood/Getty Images
  • A new study finds there are optimal times of day for achieving specific goals with exercise.
  • The research shows that for women, in particular, exercising in the morning or evening produces different results.
  • The study also includes the effect of exercise times on an individual’s mood.

Not everyone exercises for the same reason. For some, exercise is a means of addressing a health issue such as hypertension. Some work out to build strength in one part of the body or another, and some to improve their mood.

A new study suggests the time of day at which a person exercises may produce different results. In addition, those results are not the same for women and men.

Professor Paul J. Arciero, lead author of the study and professor at the Health and Human Physiological Sciences Department at Skidmore College in New York, tells BBC News that the best time for exercise is when people can fit it into their schedules.

Nonetheless, the study reveals certain time periods when individuals are most likely to achieve specific exercise goals.

Dr. Asad R. Siddiqi, assistant professor of physical medicine and rehabilitation at Weill Cornell Medicine in NYC, who was not involved in the study, told Medical News Today:

“I appreciated the authors’ stated goal of adding to our understanding of the effects of training on female athletes and how that may differ from male athletes.

“Women are notoriously underrepresented in the medical literature, and even hypothesizing that there may be a difference between how different biological sexes respond to exercise indicates a level of thoughtfulness and nuance that has long been missing from scientific inquiry.”
— Dr. Asad R. Siddiqi

The study was published in frontiers in Physiology.

The researchers tracked the benefits of exercise in a group of 30 women and 26 men who were assigned to exercise in the morning — specifically between 6:00 to 8:00 am — or in the evening from 6:30 to 8:30 PM.

All participants were healthy, non-smoking, athletically trained individuals.

The participants trained according to the PRISE (Protein pacing intake combined with Resistance functional, Interval sprint, Stretching, Endurance exercise) exercise and fitness paradigm developed by Dr. Arciero.

All participants followed a designed healthy meal plan and intake was similar in morning and evening groups.

The authors of the study measured a range of outcomes, including muscular strength, endurance and power, body composition, systolic/diastolic blood pressure, respiratory exchange ratio, and mood states, as well as their dietary intake.

Dr. Siddiqi cautioned that the participants “were all healthy, active, lean, and weight-stable individuals, which may not be particularly reflective of the habits, demographics, or goals of the larger population.”

He noted, in particular, that they were middle-aged adults with no cardiovascular disease. Thus, this would not be representative of the general population.

One of the unique aspects of the study is its exploration of exercise time of day on mood.

“[F]or the first time, we show that exercise time of day significantly alters mood state in women and men,” Dr. Arciero told MNT.

“Specifically, women who exercise in the [p.m.] significantly boost overall mood state compared to those exercising in the morning.”
— Prof. Paul J. Arciero

Dr. Siddiqi also pointed out another interesting finding:

“The men studied had greater improvement in perceived mood state than women. Exercise seemed to decrease tension, depression, anger, substantially in men regardless of time of day, whereas improvements in tension and depression were only seen in women who exercised at night.”

He added that studying mood is inherently more difficult due to its reliance on self-reporting.

All participants showed improvements in all areas after the 12-week trial. However, the nature of improvements varied.

  • Women who exercised in the morning reduced more total fat and abdominal fat, lowered their blood pressure to a greater degree, and increased lower body muscle power.
  • Women who exercised in the evening saw more improvement in their upper body muscle strength, mood, and satiety.

The effect was less pronounced in men. However, there were differences:

  • Men who exercised at either time of day improved their physical performance.
  • Men who exercised in the evening saw benefits in heart and metabolic health, as well as lower fatigue.

Dr. Arciero noted that “a direct comparison” between women and men was not the goal of the study.

“However,” he said, “several potential mechanisms for the differences between women and men with regards to their response to exercising at different times of the day may include; variations in neuromuscular function, capillary density, hunger responses, and fat metabolism between women and men.”

“[These differences] suggest molecular, endocrine, metabolic, and neuromuscular factors likely contribute to these diurnal variations in health and physical performance outcomes between women and men.”
— Prof. Paul J. Arciero

“The precise mechanism,” Dr. Arciero continued, “is not clear, but may be related to neuro-hormonal-psychological effects of exercising later in the day as a form of a ‘stress-reliever’ that may also favorably impact sleep quality. It’s interesting to note that [p.m.] exercise in men also significantly reduced feelings of fatigue.”

The study’s findings suggest that people consider the time of day at which they will exercise as they develop exercise or fitness programs with their physicians, added Dr. Arciero.