What is circadian rhythm?
Circadian rhythm is otherwise known as the internal, natural clock. It responds to light and darkness, adapting the body to the time of sleep or wakefulness. Every cell in the body has receptors that respond in a specific way to information sent by the brain regarding each successive stage of the rhythm of day and night.
It is the circadian rhythm that responds to morning wakefulness (including by increasing blood cortisol levels) and evening fatigue (including by increasing blood melatonin levels). Circadian rhythm varies in people of different ages – children, teenagers, adults and the elderly function differently throughout the day. Physiological changes related to, among other things, changes in hormone concentrations throughout the day can either favour or hinder effective workouts.
Workout in the morning
Above all, a morning workout carries a lot of benefits related to the day’s schedule. By doing the workout first thing in the morning, we can devote the afternoon hours to other things – meeting loved ones, hobbies, studying, daily household chores or leisure.
Many people choose to do their morning workouts on an empty stomach, expecting faster and better results compared to workouts done after eating. Unfortunately, workouts performed on an empty stomach do not yield significantly better results compared to workouts performed at other times of the day. As for training first thing in the morning – the rate of fat burning is irrelevant here and should not be taken into account as a factor in deciding whether to do the workout in the first or second half of the day.
Keep in mind that physical exercise is associated with increases in the heart rate, blood pressure and body temperature. These physiological changes are also accompanied by an increase in cortisol (the stress hormone), as our body interprets these symptoms as a stressful situation. Cortisol is a very important part of the circadian rhythm – we experience its highest concentration in the morning to wake up from a night’s sleep and prepare for the tasks that await us during the day.
As the hours pass, the concentration of cortisol in the blood drops to allow us to fall into a deep sleep in the evening. From this perspective, a morning workout will be more advantageous, because by doing the workout in the morning we will avoid the evening elevation of cortisol, when it should naturally be low. According to research, morning physical activity can promote more spontaneous physical activity in the second part of the day.
Advantages of morning workout:
- more energy and spontaneous physical activity in the second half of the day,
- interaction with morning blood cortisol levels,
- free time in the second half of the day.
Disadvantages of morning workout:
- getting up early (often at the expense of sleep duration),
- the workout is most often performed on an empty stomach (individual issue – some people experience a decrease in strength and performance without a pre-workout meal).
Afternoon or evening workout
Training in the afternoon or evening saves us from getting up in the morning and is the option chosen by the vast majority of people who train, as can be seen in the attendance at fitness clubs or other sports facilities.
In terms of circadian rhythm, the afternoon is the time when our physical capacity is greatest. On average, between 2 p.m. and 6 p.m., we have the highest body temperature throughout the day with the lowest heart rate and blood pressure at the same time, and this prepares our body well for exertion. In the afternoon, our body also distributes oxygen differently, which is associated with a more efficient delivery of oxygen to the muscles used in the workout. In the second half of the day we also have the fastest reflexes and reaction time, which can be important for those preparing for all kinds of competitions.
However, a workout done too late can disrupt the circadian rhythm by “waking up” the body too much at a time when it should be quieting down and producing melatonin before bedtime. It’s all due to cortisol, the concentration of which in the blood under normal conditions in the evening should fall. Intense training can cause it to increase, which in turn can make it more difficult to fall asleep and fall into the deep phases of sleep that we need for a proper night’s rest.
Advantages of afternoon workout:
- interaction with the circadian rhythm,
- the most optimal time to train in terms of physical performance,
- usually, such training takes place after several meals consumed during the day (optimal energy level).
Disadvantages of afternoon workouts:
- performed too late, it can make it difficult to fall asleep,
- with an evening workout, the post-workout meal is often skipped.
What is the best time of day to train?
Both training in the morning and in the afternoon has their pros and cons. Therefore, the best time to train is one that is individually tailored to your training goal and the daily schedule. If you are training with a specific sports goal in mind, such as taking part in a competition, then it is worth choosing the time that is most optimal in terms of physical performance, namely the afternoon. If our training goals are related to improving your figure, maintaining health or simply to recreational physical activity, the time of training will be of less importance here. It is worth remembering that a workout done at any time of the day will bring us more benefits than no workout due to the wrong time. However, we should bear in mind the length of sleep – any workout done at the expense of sleep in the long run may bring us more negative than positive results.