A study was conducted to clarify the validity and availability of inclination of exponential curve-fitting model for oxygen uptake (VO₂) and heart rate (HR) during incremental exercise (IECOH) as an index of cardio-pulmonary functional reserve in healthy subjects. A treadmill exercise test was used to measure the VO₂ (L/kg/min) and HR (beat /min) during incremental exercise of all subjects. The IECOH was derived from the following equation : HR=A⋅exp^B·VO₂. The constant “B” represents the IECOH. The following three identifications were made : 1) the relationship between maximal oxygen uptake (VO₂max) and IECOH in 82 healthy males ; 2) the relationship between IECOH and age in 428 healthy males and females ; 3) the effect of physical training in 8 healthy males.
There was inverse correlation between IECOH and VO₂max (r= -0.824) . And also, there were inverse correlations between IECOH detected from submaximal tests and VO₂max (above r=-0.6) . There were no differences in the IECOH detected from maximal and submaximal tests. In Bland-Altman plot method, accuracy of measurment in the IECOH detected from submaximal exercise test was precise. There was a significant relationship between IECOH and age in male and female subjects (r=0.499 and r=0.310, respectively) . Physical training increased VO₂max and decreased IECOH significantly. The VO₂max before and after physical training correlated inversely with the IECOH before and after physical training (r=-0.514) .
In conclusion, these results suggest that IECOH is adequate and useful as an index of cardio-pulmonary functional reserve which can be measured by the submaximal exercise test in healthy subjects.