Data were entered into a spreadsheet (Quattro Pro) from which means and standard deviations were performed. A program (Statistical Graphics Corporation, Bethesda, Md) was used to compare regression lines between oxygen uptake and work rate. Students t-tests for paired observations were used to evaluate differences between measured and predicted maximal oxygen uptake.
All subjects completed the 2 exercise tests without complication. Hemodynamic and gas exchange variables at rest and maximal exercise for all subjects are presented in Table 2. Characteristics of the ramp test are presented in Table 3. Table 4 contrasts the regression equations and correlations between measured oxygen uptake and treadmill time in the present and previous studies. The relationship between measured and predicted oxygen uptake throughout exercise is illustrated in Figure 2. The relationship between measured and predicted maximal oxygen uptake is illustrated in Figure 3. Figure 4 compares maximal MET values predicted from a specific activity questionnaire vs those achieved on the treadmill.
Table 2—Hemodynamic and Gas Exchange Data at Best and Maximal Exercise
|Author||Protocol||RegressionEquation||Mean Maximal Uptake ±SD, ml/kg/min||r||Standard Error of the Estimate|
|Bruce et al||Bruce||Y = 3.29X + 4.07||37.3 ±8.2||0.93||34.9|
|Pollock et al||Bruce||Y = 4.33X —4.66||40.0 ±7.2||0.88||0.096|
|Roberts et al*||Modified||36.8±6.6||0.93||2.56|
|Balke||Y = 3.91X —8.88|
|Froelicher et al||Bruce||Y=3.18X—0.59||44.5 ±5.8||0.82||3.34|
|Martin et al||Balke||Y = 1.25X + 9.42||41.6±5.0||0.86||2.65|
|Myers et al (present study)||Ramp||Y=.72X+.3.67||33.1 ±10.7||0.87||4.35|
Table 3—Characteristics of the Ramp Test
|Data||Mean ± SD|
|Heart rate, beats/min||66± 11|
|Systolic blood pressure, mm Hg||136 ±20|
|Diastolic blood pressure, mm Hg||88± 16|
|Heart rate, beats/min||168 ±17|
|Systolic blood pressure, mm Hg||203 ±21|
|Diastolic blood pressure, mm Hg||90± 13|
|Perceived exertion||18.9± 1.3|
|Ventilation, L/min, BTPS||101.9 ±35|
|Oxygen uptake, L/min, STPD||2.819 ±0.952|
|Oxygen uptake, ml/kg/min||33.13 ±10.7|
|COz production, L/min, STPD||3.288± 1.199|
|Respiratory exchange ratio||1.16±0.14|
Table 4 ’—Comparison of the Ramp Treadmt to Previous Studies Relating Treadmill Time or Workload to Measured Oxygen Uptake in Normal Subjects
|Mean ± SD||Range|
|Ramp rate, % grade/min||2.32 ±0.82||0.5-4.1|
|Rate of change in speed, mph/min||1.18 ±0.45||0.4-2.4|
|Peak speed, mph||3.3 ±0.4||2.5-4.5|
|Peak grade, %||16.0±5.6||3.5-25|
|Peak treadmill time, min||9.47 ±1.8||5.4-14.7|
|Peak predicted maximal oxygen uptake, ml/kg/min||37.7 ±10.7||18.4-60.3|
Figure 2. The relationship between measured and predicted oxygen uptake each minute throughout exercise. The correlation coefficient between the two variables was 0.93 (SEE = 3.96 ml/kg/ min, p.
Figure 3. The relationship between measured and predicted maximal oxygen uptake. The correlation coefficient between the two was 0.87 (SEE = 4.35 ml/kg/min), p <0.001). The regression equation was Y = 0.72X + 3.67.
Figure 4. The relationship between exercise capacity, expressed in METs, estimated from a specific activity questionnaire (Y axis) and that calculated from treadmill speed and grade at peak exercise (X axis).