Influence of work rate on the determinants of oxygen deficit during short-term submaximal exercise: implications for clinical research.
OBJECTIVE
The effect of increasing work rate was studied on the determinants of the oxygen deficit.


METHODS
Exercise testing was performed on a treadmill and gas exchange was measured on a breath-by-breath basis. Eleven healthy subjects, aged 18-25 years, performed three square wave exercise tests of different intensity. Before exercise, gas exchange was measured at rest in the standing position for 3 min, followed by a 6-min square wave exercise test, randomly assigned at 4, 8 or 12% inclination. Immediately after exercise the recovery gas exchange was determined for 3 min. To calculate oxygen deficit, the oxygen uptake (O2) values at onset of exercise were subtracted from the steady-state value, the differences were cumulated and expressed as a percentage of the total oxygen cost for the 6-min exercise.


RESULTS
The oxygen deficit increased significantly (P<0.001) with increasing work rate (6.1 +/- 1.4% for 4%, 8.4 +/- 2.1% for 8% and 9.4 +/- 1.7% at 12% inclination). This resulted from a somewhat slower increase of O2 at the onset of exercise at the highest work rate, reflected by a significantly higher time constant for O2 at 8 and 12% (24.6 +/- 7.3 s at 8% and 24.1 +/- 6.3 s at 12% versus 20.2 +/- 8.1 s at 4%). More importantly a significantly higher steady-state value for O2 was found at the highest exercise level, compared with the other exercise intensities.


CONCLUSIONS
The higher oxygen deficit at the highest level of exercise is determined by a slower time constant and a higher asymptote value for O2.
Reybrouck
Tony
T
Department of Cardiovascular Rehabilitation, University Hospital Gasthuisberg, 3000 Leuven, Belgium. tony.reybrouck@uz.kuleuven.ac.be
Defoor
Johan
J
Bijnens
Bart
B
Mertens
Luc
L
Gewillig
Marc
M
D000328:Adult; D005080:Exercise Test; D005260:Female; D006706:Homeostasis; D006801:Humans; D007700:Kinetics; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D011659:Pulmonary Gas Exchange; D015203:Reproducibility of Results; D013997:Time Factors