The aim of this study is to compare the relation between ventilation (VE) and oxygen uptake (VO2) [VO2=ƒ(VE)] and between heart rate (HR) and VO2 [VO2=ƒ(HR)]. Each one of the subjects performed three types of activities of different intensities (walking without load, walking with load and intermittent work). VO2, VE, and HR were measured continuously by using indirect calorimetry and an electrocardiogram. Linear regressions and coefficients of determination (r2) were calculated to compare the relation VO2 =ƒ(VE) and VO2 =ƒ(HR) for two different regroupings: by session duration (r2session) and by subject (r2subject). Results showed that r2session of the relation VO2 =ƒ(VE) were significantly higher than those of the relation VO2 =ƒ(HR) for steady state activities (walking with or without load during 3 or 6 min, p < 0.01) and for activities without oxygen consumption steady state (walking with or without load during 1 min, p < 0.01 and intermittent work, p < 0.05). VE is more strongly correlated with VO2 than with HR. This is a very promising approach to develop a new method to estimate energy expenditure.