Physical exercise triggers various physiological responses including a marked increase in muscle blood flow and oxygen delivery in order to support muscle activity. How muscle blood flow is controlled is currently unclear.

The primary purpose of this study is to establish the respective contribution of metabolic (linked to energy requirements) and mechanical (linked to muscle tensions) signals in the exercise hyperemia and the possible role of the red blood cells.

Vasodilation and muscle blood flow during exercise are controlled by ATP released in the plasma from the red blood cells in response to a combination of metabolic and mechanical signals applied on the vasculature.

Inclusion Criteria:

• Non smoker or having stopped smoking for at least 5 yr
• Practice sports: physical activity level will be evaluated with a questionnaire (de Baecke et coll., 1982) and will give an activity index greater than 6 together with a VO2max greater than 50 ml/kg/min
• Body mass index lower than 25
• Registered to the French Social Security system
• Providing a written and informed consent to participate in the study

Exclusion Criteria:

• History of venous or arterial thrombo-embolic events
• Bad perfusion from the cubital artery
• Unable to understand the information notice
• Subject exposed to law investigations or with financial dependancy
• Subjects feeling unwell whan seing blood.
• Subjects advised to not practice sport.
• Musculo-tendinous or articular issues with the lower leg
• Respiratory, cardiovascular or metabolic pathologies
• Current medical treatment that can not be stopped 7 days before the experiment.

Subjects will be students recruited in the Faculty, sports clubs...