There may be an optimal time of day for exercise, and it's different for women and men

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  • If you can't decide whether to exercise in the morning, afternoon or evening, new research might help you out.
  • The best time of day for exercise depends on what you want to achieve from your training.
  • However, it also depends on whether you are a man or a woman, the findings suggest.

Regular physical exercise can do wonderful things for your mind and body, but there may be an optimal time of day to achieve the best result, depending on what your aim is – and this may differ according to your sex.

The researchers behind a new randomised controlled trial, involving 27 healthy and active women and 20 healthy and active men, tested the effects of a varied fitness programme, which included sprints, stretching, resistance, and endurance training. Participants exercised four days a week over 12 weeks. Participants were between 25 and 55 years old. 

While half the group completed their daily exercise routine in the morning before breakfast, the other half did so before dinner in the evening. The whole group followed a specifically-designed meal plan for the duration of the study.

Different advantages 

The findings revealed that all the participants showed significant improvements in their fitness and health, but that women burned more body fat during morning exercise, while evenings had a bigger impact on men.

For example, women who exercised in the morning burned 7% more abdominal fat than women who exercised in the evening. The same result was seen with reducing blood pressure. Additionally, morning exercise resulted in greater leg strength.

On the other hand, women who exercised in the evening had greater benefits in their upper body strength, their mood, and their food cravings. The researchers also noted muscle power improved by nearly 30% compared to those who exercised in the mornings.

"Based on our findings, women interested in reducing belly fat and blood pressure, while at the same time increasing leg muscle power, should consider exercising in the morning,” first author and physiologist Paul Arciero from Skidmore College in the US, said in a news release.

He added: “However, for women interested in gaining upper body muscle strength, power and endurance, as well as improving overall mood state and food intake, evening exercise is the preferred choice.”

What about men?

Male participants were generally less affected by the time of exercise. However, Arciero explained that “evening exercise is ideal for men interested in improving heart and metabolic health, as well as emotional wellbeing.” Evening exercise also decreased fatigue by more than 50%, the team found.

Scientists previously looked at the different effects of morning and evening exercise. A study published this year showed how the body might produce different signalling molecules in an organ-specific manner after exercise, depending on the time of day. These signals impact health, sleep, memory, and exercise performance. 

The authors of a 2013 review, looking at 70 different exercise types and times, concluded that “time-dependent exercise has different outcomes, based on the exercise type, duration, and hormone adaptation.” 

However, despite the numerous past studies on this topic, there has been a lack of data on diverse exercise routines, and many of the studies have focused on males only. The current study is the first to implement a diverse exercise regime and assess its impact on both women and men – although it, too, does not come without limitations. 

Most of the participants were Caucasian and physically fit, noted the authors, although Arciero told the BBC that the programme may work on people who are overweight or obese. "They have more opportunities to benefit," he said.

Why this difference?

It remains unclear, but the researchers refer to the fact that men and women have different internal (circadian) rhythms – the natural 24-hour cycle that is our body’s internal clock.

“This study provides novel insight into the impact of exercise time of day (ETOD) and associated circadian rhythms on physical performance, body composition, cardiometabolic health and psychological mood state outcomes in separate cohorts of healthy, exercise-trained women and men performing exercise either early in the morning (6:00–8:00 am) or later in the evening (6:30–8:30 pm), consuming a similar diet,” wrote the authors.  

Healthcare clinicians, as well as fitness trainers and coaches, should, therefore, bear in mind the time of day when making exercise and physical activity recommendations to patients or clients, they said.

The findings were published in Frontiers in Physiology.

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