Comparaison des réponses physiologiques lors d’un exercice incrémental maximal sur vélo immergé et sur terrain sec : aspects biomécaniques, cardiopulmonaires et hémodynamiques

Water immersion can affect hemodynamic and cardiorespiratory responses during exercise relative to exercise on dry land. However, according to our knowledge, VO2 and hemodynamic responses have never been compared during exercise on immersible ergocycle (IE) and dryland ergocycle (DE) at the same level of external power output (Pext). In this regard, the first study of this thesis has proposed a method to calculate accurately the Pext deployed by participants using a model of IE during chest level immersion exercise, since the Pext from pedalling rate (rpm) in water was still undetermined to date. The Pext expressed in W was calculated by multiplying the total force overcoming the resistance of the water on the system movement (pedaling system and legs) by the velocity (m/s) of the pedal. We favored this approach since it takes into consideration the resistance of water on the lower limbs and not only the pedaling system. The quantification of Pext allowed us subsequently to compare the physiological response of the immersion during exercise on an IE when compared to the same Pext on a DE. The results shown that VO2 (p< 0.0001) and C(a-v)O2 (p<0.0001) were significantly lower during exercise on IE relative to DE. Among hemodynamic variables, stroke volume (p<0.05) and cardiac output (p<0.05) were higher and heart rate (p<0.05) lower during exercise on IE. Because physiological responses were different for the same Pext on IE and DE, we have studied the relationship between various expressions of relative exercise intensity (% VO2max, %HRmax, % VO2 reserve (% VO2R) and %HR reserve (%HRR)) in order to obtain the more appropriate method for exercise intensity prescription when using an immersible ergocycle (IE). The results shown that %HRR vs % VO2R relationship appears to be the most accurate for exercise training prescription on immersible ergocycle (IE). Thus, absolute cardiopulmonary responses (VO2 and HR) during exercise on IE were different to that of DE but relative intensity was found similar at a similar Pext on both immersible and dryland ergocycle. This study offers a new tool to better prescribe, control and individualize exercise intensity on IE in young healthy subjects. Finally, a last study comparing parasympathetic reactivation after maximal incremental exercise performed on IE (immersion at the chest) and DE, showed that short-term parasympathetic reactivation was more predominant on IE (i.e. delta 10 delta 60 and T30, p<0.05). This suggests that, after maximal exercise on IE, parasympathetic reactivation was accelerated relative to recovery after maximal effort on DE in healthy participants. In conclusion, we proposed a method to calculate the Pext on different models of IE from rpm and an equation for the calculation of VO2 during exercise on IE. We demonstrated that during exercise on IE the hemodynamic and cardiorespiratory responses are different from those on DE at the same Pext and a method for exercise prescription and control on IE. Finally, we demonstrated that short-term parasympathetic reactivation was accelerated during post-maximal exercise recovery on IE as compared to that on DE.

Keyphrases: Central hemodynamic responses, Immersed ergocycle, External power output, Oxygen uptake, Exercise prescription, Parasympathetic reactivation