Chronicles

We all know that physical exercise can increase the strength of our muscles and that its practice promotes a healthier life, but researchers have already proven that exercise practice is also important for the maintenance of our circadian rhythm.

The circadian rhythm consists in oscillations of approximately 24 hours inside our organism and include the sleep/wake cycles, the production of hormones (such as cortisol) and also the cycles in body temperature. Throughout the 24 hours of a day, these oscillations are synchronized with external stimuli, for instance light exposure (day/night), diet and even exercise. The circadian rhythm of our body is controlled by a system of biological clocks, the central clock of which, is localized in a brain area named suprachiasmatic nucleus of the hypothalamus. This central clock is the master of all the peripheral biological clocks that exist in all the cells of our body, such as those in the stomach, intestines, liver, kidneys and even in the skeletal muscle. These peripheral clocks “tic-tac” at the rhythm of the central biological clock of the hypothalamus. The function of these internal clocks is regulated or dysregulated by the number of hours we sleep, our dietary patterns and physical activity. Alterations in our lifestyle habits, such as snacking and not sleeping enough, dysregulate the biological clocks and compromise a healthy life. In fact, the misfunctioning of these biological clocks is associated to several sleep disorders as well as the development of several other diseases.

It is well known, for instance, that meals regulate our biological clocks. For example, breakfast serves to wake up our internal clock, letting him know that the day is about to start. This ensures that our organism is in the same “time zone” as the course of the day. An intake of foods with fats, or snacking in between meals, can alter the normal ticking of our internal biological rhythms and result in weight gain. This phenomenon is very well characterized in individuals that perform shift work, who have a higher predisposition for obesity and other metabolic disorders given their irregular sleep patterns.

Besides the influence of meals, physical exercise is also a regulator of circadian rhythms. Exercise practice increases the temperature of the body, this rise hitting our internal clock. The practice of exercise can also regulate the brain circuits that control food intake. Some studies show that regular exercise of moderate intensity is able to reverse the molecular alterations on the circadian rhythms that are caused by the intake of a diet rich in fats and by obesity itself.

Considering this relationship between exercise practice and the maintenance of biological clocks, several studies were undertaken to determine the processes or mechanisms responsible for this link. Regular exercise practice and the synchronization of the internal biological clocks with the environment, promote a healthy sleep, contributing to the strengthening and precision of the ticking of our internal clock. On the other hand, alterations on sleep patterns, such as insomnia or sleep deprivation alter the central as well as the peripheral clocks, namely in the muscle, with the potential of abolishing the beneficial effects of exercise practice. This happens because the biological clock in the muscle cells is very important for the function of the muscles. Therefore, sleeping an adequate number of hours (8-10h for adolescents, 7-9h for adults and 7-8h for old people) is crucial for a good physical condition.

The time of the day at which exercise practice takes place is also important for the performance of the muscle and for the global result of exercise. Studies show that the peak of activity for the skeletal muscle is reached between 16:00 and 18:00h in the afternoon. This does not mean that exercise practice in the morning is not beneficial, but if performed during the afternoon, it will be more efficient in what regards to energetics (with a reduced sensation of tiredness and exhaustion after training). Exercise within this timeframe is also associated with a higher success in weight loss endeavors, given that the circadian body temperature peak is also found within this interval. Together with this peak in body temperature, exercise practice will promote additional energetic expenditure and along with it, an increased weight loss. Nonetheless, it is important to note that each one of us has their own rhythm and these can be widely different from one person to another.

In this context, a proper functioning of our internal biological clocks is reflected in our well-being. Respecting our own rhythms, and winding the clocks with a healthy diet, exercise practice tailored to our physical condition and age, and maintaining regular sleep patterns, both in quantity and quality, is essential for our well-being. This way, we will preserve the “Tic-Tac” of our circadian rhythms, which will contribute for a longer and healthier life.

Authors: Cláudia Cavadas is a Principal Investigator at the Center for Neuroscience and Cell Biology (CNC), University of Coimbra (UC) and Professor at Department at Faculty of Pharmacy (FFUC) of University of Coimbra. Ana Rita Álvaro and Sara Silva are Researchers at the Center for Neuroscience and Cell Biology (CNC), University of Coimbra (UC) and Laetitia Gaspar is PhD student at at the Center for Neuroscience and Cell Biology (CNC), University of Coimbra (UC).

The project: This chronicle results from the collaboration between the Center for Neuroscience and Cell Biology (CNC) of the University of Coimbra, the European Advanced Training Network FOIE GRAS (http://www.projectfoiegras.eu), the Erasmus+ Program and the Academic Sports Federation University (FADU) in the scope of the European University Games Coimbra 2018.

Coordination: Anabela Marisa Azul, João Ramalho-Santos, Mireia Alemany i Pagès, Paulo Oliveira and Sara Varela Amaral

Illustration: Rui Tavares