Biomarkers of physical activity and exercise.

Traditionally, biomarkers have been of interest in sports in order to measure performance, progress in training and for identifying overtraining. During the last years, growing interest is set on biomarkers aiming at evaluating health-related aspects which can be modulated by regular physical activity and sport. The value or concentration of a biomarker depends on many factors, as the training status of the subject, the degree of fatigue and the type, intensity and duration of exercise, apart from age and sex. Most of the biomarkers are measured in blood, urine and saliva. One of the main limitations for biochemical biomarkers is that reference values for blood concentration of biomarkers specifically adapted to physically active people and athletes are lacking. Concentrations can differ widely from normal reference ranges. Therefore, it is important to adapt reference values as much as possible and to control each subject regularly, in order to establish his/her own reference scale. Other useful biomarkers are body composition (specifically muscle mass, fat mass, weight), physical fitness (cardiovascular capacity, strength, agility, flexibility), heart rate and blood pressure. Depending on the aim, one or several biomarkers should be measured. It may differ if it is for research purpose, for the follow up of training or to prevent risks. For this review, we will get deeper into the biomarkers used to identify the degree of physical fitness, chronic stress, overtraining, cardiovascular risk, oxidative stress and inflammation.