The oxygen cost of the treadmill speed and grade was calculated using equations commonly applied for predicting oxygen uptake from treadmill and cycle ergometer work. An example of the ramp test is illustrated in Figure 1. With the exception of the protocol, all exercise data, including hemodynamic, gas exchange, and perceived exertion were collected as on the initial test. The 10-min duration was used only as an estimated goal, so that the maximal external work rate on the second test would correspond to the measured maximal oxygen uptake obtained on the baseline test; however, exercise was continued to volitional fatigue.
Respiratory Gas Exchange
Respiratory gas exchange variables were determined continuously throughout the exercise test (using the Medical Graphics Corporation 2001 System). Gas exchange variables analyzed were as follows: oxygen uptake (Vo2, ml/kg/min, STPD); carbon dioxide production (Vco2, L/min, STPD); minute ventilation (Ve, L/min, BTPS); oxygen pulse (Vo*, ml/min divided by heart rate); and respiratory exchange ratio (RER, Vco2 divided by Vo*). One-minute ventilatory samples were used throughout exercise. However, when measured and predicted maximal oxygen uptake were compared, an eight-breath moving average sample corresponding to the treadmill speed and grade at peak exercise was used.
Figure 1. The ramp treadmill test. Following a 1-min warm-up at 2.0 mph/0% grade, the rate of change in speed and grade was individualized to yield the work rate (X axis) corresponding to maximal oxygen uptake (Y axis, obtained from the baseline test) in 10 min.