A good portion of people who exercise regularly do so to improve their physical condition and health, something more necessary than ever in this 2020 of forced sedentary lifestyle in which the pandemic has also affected our mental health.
We usually quantify the distance traveled, the time and the intensity of the exercise because these parameters influence the result of the physical activity carried out. However, there are variables that are not usually valued but that also condition the effects of exercise. One of the most forgotten is the choice of the best hours of the day to carry out physical activity.
Recommendations on this matter are not an easy task because it is a very personal matter that, in addition, is usually conditioned by many factors. In the following lines we will show some of the parameters we should consider when choosing the best moments of the day for physical exercise.
One of the variables that can most affect the effect of physical activity is the quality of the air breathed during exercise. In this regard, we must remember that international organizations warn of the presence of high levels of pollution in the air we breathe. Covid-19 reduced this problem during lockdowns, but it will not solve it in the long term.
When air pollution levels are high, exercising outdoors may not be as beneficial as we think. The amount of air that reaches our lungs in a situation of effort is much greater than that which would arrive at rest. Thus, if we run intensively in an area with polluted air, the amount of toxic substances that will enter our body will be much greater.
For this reason it is very important choose the time of day and the place where the environmental conditions are the most favorable. To achieve this objective, the habit of consulting the reports published in real time by the country’s air quality networks should be established. For example, the Air Quality networks of the Autonomous Communities offer daily reports on the concentration of pollutants in the air. Data for all of Spain can be consulted in the air quality viewer of the Ministry for the Ecological Transition and the Demographic Challenge.
This information makes it possible to know with enough precision the hours of the day in which the concentration of pollutants is lowest in the different localities of this territory. In the case of the polluting gases that are expelled directly by the chimneys and the exhaust pipes of the vehicles (CO₂, NOx, PM) the least recommended hours for physical activity are those that coincide with the highest vehicle traffic and with the greater industrial and economic activity in urban centers.
On the other hand there are gases, called indirect, which have a less intuitive but equally dangerous behavior. This is the case of tropospheric ozone (O₃), which tends to maintain higher levels in summer and in the central hours of the day, due to the influence exerted by solar radiation on its formation. This circumstance can occur even in areas far from the sources of pollution.
In short, if we want to reduce exposure to air pollution during physical exercise, we should check the levels of pollution present at the time and place where said activity is going to take place to choose the most propitious moment.
Nor can we forget the environmental conditions linked to temperature, relative air humidity, solar radiation and wind speed. All these factors can be modified throughout the day. Therefore, when it is hot, it is necessary to choose the time when these conditions are most favorable for the practice of physical activity. These time slots usually coincide with the beginning and the end of the day.
In general terms, it can be said that the practice of physical exercise in hot environments implies a significant overload for anyone. Especially for the population with cardiovascular risk (people with heart problems, diabetes, overweight or hypertension).
In this sense, intense physical exercise should be avoided at temperatures above 28 superioresC or even lower when the wind speed is low and the relative humidity of the air and solar radiation are high. This is due to the fact that when the atmosphere is already saturated with water, the evaporation rate of sweat deposited on the surface of our skin is slower, limiting the release of excess heat and increasing the loss of water and mineral salts.
With respect to solar radiation, it is important to remember that the thermal stress that our body bears is greater when physical exercise is carried out in the central hours of sunny days and hot. Especially if the activity is carried out with dark clothing, on pavements or in light-colored environments (beach sand, snow, white sidewalks).
On the contrary, the wind speed is a factor that helps to get rid of the heat on hot days, but that on very cold days can promote hypothermia.
Although teleworking has disrupted the lives of many people, the current rhythms of life implanted in our society force us to exercise after the workday or when we have freed ourselves from personal commitments. This moment usually coincides with the last hours of the day. The problem is that the final part of the day is the time when we tend to find ourselves the most tired.
Thus, the training session will not be performed with the same intensity as the one we could achieve in the case of exercising first thing in the day. In addition, doing physical activity at the end of the day can delay dinner time, increase the amount of food eaten shortly before bedtime, and increase the level of arousal of the subject in the hours close to sleep.
Consequently, all these factors can delay or compromise the quality of sleep.
Another question that often generates doubts in the sports population is whether to exercise before or after meals. It is evident that high intensity physical activity is not appropriate immediately after main meals, especially if the food intake has been copious, although a very light physical activity would be recommended, such as a walk.
That said, there are trends today that promote physical exercise after a long fast. Although these could be applied in elite athletes specialized in long distance, they are not recommended for those who are starting out in physical activity or who seek to improve the quality of their body weight.
This is due to the fact that when the person carrying out the effort is hungry, the duration, intensity and motivation with which the physical activity is going to be carried out is usually lower. This means that the total caloric expenditure of the training session is lower than that which would have occurred if the session had been carried out without the feeling of hunger that accompanies fasting.
Likewise, People who engage in physical activity on an empty stomach (even with hypoglycemia) often experience irritability, a feeling of malaise, dizziness, lipothymia, and inattention during exercise. On many occasions, this leads to a higher prevalence of injuries and accidents. In addition, the feeling of hunger that accompanies fasting does not seem the best option for people to loyalty and adhere to the practice of physical activity.
It is recommended that the person who is going to exercise has a light meal (a piece of fruit, a yogurt, an infusion, nuts) approximately 30 minutes before of the training session. With this measure, we will feel with more energy and motivation to train more intensely, for a longer time and, also, with a less sensation of hunger after exercise that will reduce the temptation to overeat.
Regardless of particular preferences, the most recommended time slot to carry out this activity is the first thing in the morning, about 30 minutes after having eaten a light breakfast, which may be supplemented after the session.
However, it is also recommended to adapt the time of physical exercise to the factors mentioned above and, in the event that environmental conditions do not make it advisable to practice outdoors, it is always possible to choose sports or activities that can be performed in closed facilities (heated swimming pools or indoor sports facilities), something more difficult to achieve while SARS-CoV-2 is present. In addition, physical activity can be spread out at different times of the day without giving up the benefits it brings.