Lark vs. owl: morning or evening training for best performance and health outcomes?

Over the past two decades, a growing body of research has established that exercise can both affect and be affected by internal biological rhythms, particularly the day-night cycle (known as the ‘circadian rhythm’). This is why certain aspects of performance are known to be affected by the time of day that exercise is performed and why manipulating the internal ‘biological clock’ can produce better performance outcomes (see this article for a more in-depth discussion on this topic).

A number of review studies looking at the sum of research to date have found robust evidence for circadian-related variations in many performance-related outcomes, with peaks typically occurring in 

the afternoon and evening^(1-6). There’s also a clear consensus that when training for a specific event, the time of exercise training should coincide as closely as possible with the time of competition to achieve optimal performance improvements^(7,8). So for example, while your natural peak may occur in the late afternoon or early evening, if you’re competing in a morning event, regular morning training will likely yield better results on the race day itself.

Circadian rhythm and training gains

As regular SPB readers will know from previous articles, the circadian rhythm has a profound effect on physical performance, with key aspects of muscle function during exercise changing according to the time of day⁽⁹⁾. However, some research also suggests that the time of day you train may affect the training adaptations that occur following training⁽¹⁰⁾. So if you are training for fitness and health in the longer term, and not with a specific competition in mind, you may get optimal results by choosing your training time accordingly.

“As regular SPB readers will know from previous articles, the circadian rhythm has a profound effect on physical performance.”

A good example of research supporting this notion comes from a US study last year on men and women performing mixed training at different times of the day (see this article)⁽¹¹⁾. In short, the mixed training program consisted of a blend of resistance exercise, interval sprint training, stretching/yoga/Pilates and steady-state endurance exercise. The 26 male and 30 female participants trained either in the morning (06.00–08.00am), or in the evening (18.30–20.30pm). 

The results showed that in the women cohort, those who exercised in the morning had greater reductions in total (-5% vs. -2%) 

and abdominal fat mass (-10% vs. -3%) and experienced a larger drop in blood pressure (-10% vs. -3%), as well as increased lower body muscle power (13% vs. 4%). By contrast, women exercising in the evening had significantly greater gains in upper body muscle strength, power, and endurance, and also experienced improved mood and greater satiety (ie less hunger cravings) than when they trained in the morning.

Among the men, the responses to morning and evening training were much less pronounced compared to the women. However, men training in the evening experienced a significantly greater reduction in blood pressure compared to morning training, and also benefitted from increased fat oxidation (6% vs. 1%) compared to morning exercisers, along with significantly less fatigue.