Exercising in sync with your circadian rhythm: optimize workouts according to your biological clock

How does circadian rhythm work?

Most people naturally align their activities with the Earth’s natural day-night cycle, being active during the day and resting at night. This rhythm also governs our bodily functions, which operate more actively during the day and slow down at night. Interestingly, the human body maintains a roughly 24-hour cycle even without any external cues about the time of day. For this reason, it’s referred to as the circadian rhythm (Latin circa – around; dies – day). The circadian rhythm can be compared to an internal, genetically programmed ‘clock’ that governs people’s essential physiological functions.

Broadly speaking, people often refer to a single, ‘universal’ circadian rhythm. In practice, however, the term encompasses a multitude of specific cycles within our bodies: from individual cells, through tissues and organs, to comprehensive physiological processes. There are also circadian rhythms that span roughly 22 to 26 hours. Examples of these include:

• pattern of cell division (more pronounced during the night),
• endocrine rhythms – secretion of cortisol, melatonin, growth hormone, and other hormones,
• liver rhythm – regulation of glycogen synthesis,
• behavioral and mental activity rhythms,
• sleep-wake cycle,
• body temperature rhythm.

It’s clear that these rhythms influence numerous aspects of our bodily functions, significantly affecting physical activity and its outcomes. Scientists are leveraging the study of circadian rhythms to enhance the performance and efficiency of professional athletes. But can this knowledge also benefit non-professionals?

Biological clock and training

Individuals who are not professional athletes should be aware of the two main periods of peak physical capacity occurring typically between 10:00 AM and 1:00 PM, and between 4:00 PM and 7:00 PM. During these two windows, the body’s circadian rhythms are most attuned to physical activity, making them the optimal times for effective training.

Unfortunately, unless we’re professional athletes, we have to fit physical activity into our existing schedules and daily routines rather than the other way around. Nevertheless, it’s reassuring to know that simply engaging in physical activity can influence our circadian rhythms and alter the factors determining our strength, performance, and endurance based on the time of day. This implies that aligning our training with our biological clock essentially involves selecting the optimal time of day. However, each option comes with advantages and disadvantages.

A morning workout takes advantage of the naturally elevated cortisol levels in the blood that remain after waking up. Thus, the morning is great for lighter cardio workouts and activities that require precise movement techniques, learning new elements, and high levels of concentration, as our bodies handle these tasks best at this time. However, a disadvantage of morning workouts (apart from the need to get up early) is that they’re usually done on an empty stomach. As a result, morning workouts are not more effective than exercising at other times of the day.

Exercising in the afternoon or evening is more suitable for high-intensity strength or cardio workouts, like interval training. This is because the afternoon and early evening is the time when our cardiovascular system operates at its peak capacity. We tend to experience increased energy, reduced fatigue, and faster recovery. We also achieve the greatest gains in strength and performance when working out in the evening. The challenge, however, lies in ensuring sufficient rest periods and maintaining good sleep quality.

Read also: Training in the Evening – Yes or No?

Exercising at night disrupts the natural functioning of the circadian rhythm. Both physical performance and strength are reduced at night. The same exercises require more energy and oxygen in the evening compared to during the day. While we might burn more calories, the trade-off includes sleep deprivation, an increased risk of overtraining and injury, and potential negative impacts on our behavior and social life.

Should we consider our biological clock when planning our activities?

The connection between biological rhythms, exercise effectiveness, and human body capabilities has been extensively explored in scientific literature. However, scientific findings typically relate to high-level training or personalized training aimed at achieving specific competitive results.

Still, being mindful of your individual biological clock and observing your body’s natural rhythms throughout the day is important because it can improve your ability to adapt to regular exercise, maintain consistency in your workouts, and ensure optimal recovery. With this in mind, we’ve prepared some tips that will benefit not only beginners:

1. Training is not about “blood, sweat, and tears”! The issue isn’t the intensity of the workouts themselves, but rather the significant sacrifices many of us make just to begin exercising. We disrupt our routines, prioritizing exercise at the expense of sleep, nutrition, relaxation, and quality time with loved ones. This unsustainable approach can ultimately lead to giving up exercise completely. It’s more effective to adopt a ‘baby steps’ approach – slowly incorporating physical activity into your daily routine and then gradually adjusting its frequency and intensity based on your time, willingness, and needs.
    
2. Exercise consciously. It’s a good idea to keep a training diary or use tools that monitor the body’s vital functions. Popular devices like heart rate monitors, smartwatches, and workout apps enable real-time data collection, helping us better understand our biological clock. This analysis allows for training optimization, either independently or with a coach’s guidance.
    
3. Prioritize consistency. Even though the circadian rhythm is somewhat flexible and can be influenced by exercise, it’s important to remember that the body requires time to adjust to changes. These adjustments are indicated by a temporary decrease in performance, which may persist for up to three weeks. Consequently, a consistent and well-structured workout plan is far more beneficial than sporadic training sessions done ‘out of obligation’ at varying times of the day. Major modifications to the training plan should be appropriately spaced out over time.
    
4. Maintain a consistent circadian rhythm. While physical activity helps regulate the circadian rhythm, many of our daily behaviors, habits, and routines can negatively impact it. Give special consideration to factors like:

• excessive screen time, which disrupts melatonin production, with potential negative effects on sleep quality; We suggest avoiding screen use for 1 to 2 hours before bedtime.
• stimulants, such as coffee, alcohol, cigarettes, and energy drinks, can disrupt the natural rhythms of your metabolism and nervous system, and affect sleep quality;
• meals consumed irregularly, in varying quantities (ranging from none to several times the daily portion), and at inconsistent times. This can disturb the natural rhythms of digestion and rest, particularly if you choose to eat before bedtime after a whole day of fasting.
• inadequate rest – it’s not about excessive training loads, but rather an overly intense lifestyle, with too many tasks, overtime, bringing work home, or taking on new responsibilities. All of these poor habits disturb the body’s internal clock on a daily basis and, over time, can lead to serious health issues.

5. Having a solid plan is essential. To ensure training is effective and in sync with the biological clock, it must be planned with a long-term perspective. It’s crucial to evaluate how much time you can realistically dedicate to physical activity and to allocate some time for rest and recovery. Also, it’s important to consider how to balance sports with family, social, and professional commitments, as well as plan for costs related to classes, equipment, or participation in competitions. Another good idea is to discuss your aspirations, goals, and possibilities with your trainer. So, the most effective tool for aligning with the biological clock is ultimately... the calendar.

^References:

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4. ^{Grgic J., Lazinica B., Garofolini A. et al., The effects of time of day-specific resistance training on adaptations in skeletal muscle hypertrophy and muscle strength: A systematic review and meta-analysis, Chronobiology International, 2019.}
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