The type of effort exerted when running depends on both the distance traveled and the speed of execution.

In the case of a run of medium intensity (from 1500 m to 20 km), it is the aerobic system who is in demand. The body breaks down sugars and fatty acids to respond to effort without producing additional waste. This process depends on the ability to collect, transport and distribute the oxygen necessary for this degradation: the quality of breathing is therefore very important during exercise. When the body reaches its maximum oxygen consumption (VO2 max) due to intense effort, the aerobic sector reaches its limits.

If the effort is particularly intense (case of violent efforts of short duration such as the sprint, the 100 m), the aerobic system does not make it possible to respond to the effort provided. Another system, theanaerobic lactic is responsible for providing energy to the muscle. For this, the body breaks down muscle glycogen which is transformed into lactic acid and whose accumulation in the tissues will quickly pose a problem. It is therefore theoretically possible to run a 100 m freediving. If the effort is prolonged too long (generally beyond 3 minutes), the accumulation causes acidosis and violently stops the exercise.

The two energy systems can nevertheless operate simultaneously.

Running over medium and long distances is associated with weight loss, improvements in lipid profile and blood pressure as well as cardiac remodeling (1-3). It also improves the immune system, relaxation and increases bone mass.

The cardiovascular response to high intensity training in insufficiently prepared individuals, however, remains poorly understood. The half marathon, like the marathon and the long distance races, have been associated with increased oxidative stress and myocardial damage (4-9). Usually, however, the level of troponin, a biomarker that identifies damage to heart muscle cells, returns to normal 48 hours after exercise (10), and muscle rebuilds.

Current studies do not allow us to confirm that regular long distance or even ultra distance runners are more exposed to cardiovascular risks (11).

The practice of running over medium and long distances does not help build muscle mass. Above all, it improves cardiovascular performance.

Regular practitioners of running receive thousands of impacts per session that can cause various disorders such as cramps, side points, contractures, tendonitis, pubalgia or fatigue fractures. These impacts have long been suspected of favoring osteoarthritis knee in frequent runners by creating lesions in the cartilage. However, it appears that runners do not have more knee osteoarthritis than non-runners. The patellar cartilage of great runners would adapt by becoming thicker and more resistant allowing it to resist more to the intense mechanical stress to which it is exposed. On the other hand, it is certain that cartilages injured in a traumatic manner (torsion or physical contact for example) are more prone to degeneration.

Running involves a strong mental will and requires a great rigor during preparation and training. The psychological benefits observed after exercise would be allocated to running only up to about 20% against almost 80% by the placebo effect (12).

For many runners, the time it takes to complete a run is crucial. It is therefore important for them to understand the mechanics of running performance.

2 main determinants have been clearly identified: VO2Max and running economy.

VO2max

In a homogeneous group of runners, VO2max is strongly related to running performance. It is the maximum capacity of the organism to capture, transport and use oxygen. In running, it is one of the fundamental parameters of performance. It is possible to improve it because it depends on many factors:

Ventilation. Ventilatory flow and the ability to deliver oxygen from the lungs to the blood capillaries will influence VO2max. The genetic aspect plays a big role in the variability of these two parameters but several factors can deteriorate them (tobacco, physical inactivity, pollution, etc.).

The transport of oxygen through the blood. This transport depends both on the hematocrit, i.e. the volume occupied by red blood cells in the blood, on the affinity that hemoglobin has for fixing oxygen, but also on the heart itself. even, which induces a certain cardiac output. These are all factors that can be improved with training.

Peripheral circulation. The capillary density as well as the oxygen extraction capacity influence the blood circulation and therefore the maximum oxygen consumption.

Muscles. At the muscular level, the amount of myoglobin, the density of mitochondria in the cells, the type and number of muscle fibers also participate in determining this maximum consumption.

Race economy

In a group of runners with an equivalent VO2max, it is therace economy that makes the difference. So, even if it is important to have a powerful engine (V02max), it is also important to be able to save what is in the tank, in other words to make better use of its energy resources. This ability to reduce the energy cost of running can differ from runner to runner by more than 30% and therefore contributes greatly to performance (14). Several studies have shown that it is influenced by training, environment, runner’s physiology, anthropometry and biomechanics (15).

The technique. For reduce the energy cost, it is important toimprove your technique. We speak in particular of the stride, the attack of the ground by the heel, the time of contact with the ground, the position of the arms, the tension, the impulse, the position of the trunk, etc. All of these movements and factors affect energy cost and performance over long distances.

Getting used to the effort (resistance to fatigue).

The training. Running economy can be improved by 3 to 8% thanks to different training methods such as plyometrics (a set of strength training exercises focused on the tone of the skeletal striated muscles), muscle strength and resistance, exposure vibration, interval training and altitude training.

Time. Researchers have shown that the duration of the practice improves the physiology of the runner in the long term: a practitioner who has been running for more than ten years would therefore continue to transform his body by adapting it more and more to running (16).

The shoes. Studies have shown that certain shoe models (the so-called minimalist shoes weighing less than 220g each) can slightly improve running economy (13).