Different schedules = different results?

Regular exercise is linked to numerous health benefits, such as improving body composition, increasing muscle strength, reducing stress and preventing chronic diseases.

However, the question is: does the time of day you train influence your results? Science suggests that it does, and this influence can depend on several factors.

Several scientific studies have investigated the impact of the circadian rhythm - the internal “biological clock” - on physical performance, muscle hypertrophy and fat burning. However, the effects can vary according to the individual's goal and chronotype. Is it possible (or even desirable) to adjust our circadian rhythm to the demands of personal, professional and socio-economic life? This question complicates the debate and raises important reflections, which we will address throughout the article.

Circadian rhythm and physical performance

The human body operates on the basis of the circadian rhythm, a 24-hour cycle regulated mainly by sunlight. This cycle has the ability to influence physiological factors such as body temperature, hormone levels and mental alertness.

Several studies have shown that body temperature tends to peak in the late afternoon (between 4pm and 8pm), which can optimize physical performance by improving mobility, muscle strength and metabolic efficiency (Chtourou & Souissi, 2012).

In addition, you may be less willing to train intensely in the morning, especially in people with an afternoon chronotype, which we'll go into in more detail below.

However, despite these potential physiological benefits, not everyone has the freedom to adapt their workouts to the “ideal” circadian rhythm. Many work fixed hours, study at night or look after family members, making it impossible to train at the most biologically efficient time.

Here the dilemma emerges: should we adapt our circadian rhythm to external demands, or adapt training to our reality?

Chronotypes

We call chronotype the natural predisposition of each person to feel peaks of energy or tiredness at different times of the day. There are several types of chronotype:

• Morning Chronotype - the early birds, who tend to have more energy and be more productive in the morning. Individuals with this chronotype obviously tend to do better in training in the morning (Facer-Childs et al., 2015);

• Evening Chronotype - usually known as night owls, who tend to have more energy in the evening and, as a result, their workouts tend to be better at the end of the day;

• Intermediate Chronotype - this type of person has a more flexible pattern, feeling good both in the morning and in the evening and their sleeping hours can vary, as can their predisposition to training.

Although chronotypes are largely genetic, there is some circadian plasticity. Through consistency, exposure to light, sleep habits and diet, we can adjust our biological rhythm slightly - but this has limits, especially if it is done in constant confrontation with the actual lifestyle.

For example, an evening person forced to train at 6 a.m. because of work may feel less energetic, which reduces the effectiveness and enjoyment of training. On the other hand, insisting on training at night when this is detrimental to sleep can have negative long-term effects.

It is in this balance that the notion of sustainability comes into play.

Body composition and physical results

What about fat loss? The loss of body fat doesn't seem to be significantly affected by the time of the workout. The most important thing is the total calorie expenditure, the intensity and frequency of the exercise. A study published in the Journal of Obesity (Willis et al., 2012) showed that individuals who performed aerobic exercise at varying times had similar results in body fat loss.

A study by Kuusma et al. (2016) compared groups that trained in the morning and afternoon for 24 weeks. Both showed increases in strength and muscle mass, although the afternoon group had slightly greater gains in hypertrophy. This indicates that afternoon/evening training may be slightly more effective for gains in strength and lean mass, but this advantage is small and may not justify drastic changes in routine.

However, there are other factors, such as the quality of your sleep and your diet, which can be more important than the time you train.

Once again, what matters is: is it worth sacrificing your mental health, sleep or work-life balance to train at the “best” time?

Consistency

An important factor is consistency in training schedule. A study published in the Journal of Strength and Conditioning Research (2016) showed that individuals who stick to the same training schedule have greater strength gains and better performance than those who train at varying times. This is because the body ends up adapting to the usual exercise schedule and, on the other hand, if we vary the schedule frequently, we may be making it more difficult for the body to adapt.

This is due to the body adapting to the usual exercise schedule - both hormonally and behaviorally.

With this, we can conclude that regularity overcomes timing. The best time to train is the one we can stick to consistently. If morning training is the only manageable time, then it's the most effective for us - even if science points to small advantages for other times.

Conclusion

Yes, the time you train can influence your results, but this depends on multiple factors of equal (or even greater) importance:

• Individual goal (fat loss vs. strength/muscle mass gain);

• Chronotype and lifestyle;

• Sleep quality, diet and stress;

• Consistency in the training schedule;

• And above all: personal, professional and socio-economic conditions.

The idea that we should adjust our circadian rhythm to our reality is only valid up to a point - small adaptations are possible. But trying to force the body to operate against its biological clock, just to fit into a theoretical ideal, can do more harm than good.

More important than finding the absolute best schedule, it's important to choose a schedule that we can stick to over the long term and on a regular basis, respecting our biological rhythm and personal routine.

References

• Chtourou, H., & Souissi, N. (2012). The effect of training at a specific time of day: a review. Journal of Strength and Conditioning Research, 26(7), 1984–2005.

• Facer-Childs, E. R., et al. (2015). Circadian phenotype impacts the brain’s resting-state functional connectivity, attentional performance, and sleepiness. Scientific Reports, 5, 11487.

• Sedliak, M., et al. (2009). Effects of time-of-day-specific strength training on muscular hypertrophy and strength. Chronobiology International, 26(3), 576–592.

• Kuang, J., et al. (2022). Exercise training and time of day: Effect on physical performance and health outcomes. Frontiers in Physiology, 13.

• Hill, D. W., Cureton, K. J., Collins, M. A., & Grisham, S. C. (1998). Diurnal variations in responses to exercise of "morning types" and "evening types". Journal of Sports Medicine and Physical Fitness, 28(2), 213-219.

• Kuusma, M., Ahtiainen, J. P., Häkkinen, K. (2016). Strength training in the morning or evening – does it matter?. Chronobiology International, 33(4), 393–405.

• Willis, L. H., Slentz, C. A., Bateman, L. A., Shields, A. T., Piner, L. W., et al. (2012). Effects of aerobic and/or resistance training on body mass and fat mass in overweight or obese adults. Journal of Obesity, 2012: 1–10.