On issues of confidence in determining the time constant for oxygen uptake kinetics
- 1Departments of Medicine and Physiology, UCLA School of Medicine, Los Angeles, CA 90095, USA
- 2Departments of Biostatistics and Radiological Sciences, UCLA School of Medicine
- 3Exercise Science Laboratory, El Camino College, Torrance, CA 90506, USA
- Correspondence to: Dr Cooper 37-131 CHS, UCLA Medical Center, 10833 Le Conte Avenue, Los Angeles, CA 90095, USA; ccooper{at}mednet.ucla.edu
- Accepted 29 July 2003
Abstract
Background: τV˙o2 at the onset of constant work rate (CWR) exercise is a variable of aerobic fitness that shortens with physical training and lengthens with cardiopulmonary disease. Determination of τV˙o2 with sufficiently high confidence has typically required multiple exercise transitions limiting its clinical application.
Objectives: To design a protocol to determine τV˙o2 reliably but simply.
Methods: On each of three days, five healthy men performed two CWR tests on a cycle ergometer below the metabolic threshold (V˙o2θ) for blood lactate accumulation as determined by gas exchange measurements followed by an incremental work rate (IWR) test. τV˙o2 was determined (a) from the on-transit (on-τV˙o2) and off-transit (off-τV˙o2) of six CWR tests both individually and superimposed, using non-linear regression with a monoexponential model, and (b) by geometric analysis of the IWR tests (ramp-τV˙o2).
Results: Group means (SD) were: V˙o2max 3.84 (0.44) litres/min, V˙o2θ 1.88 (0.23) litres/min, steady state exercise V˙o2 1.67 (0.07) litres/min, on-τV˙o2 38.0 (5.3) seconds, off-τV˙o2 39.0 (4.3) seconds, and ramp-τV˙o2 60.8 (15.4) seconds. On-τV˙o2 correlated with off-τV˙o2 (r = 0.87), V˙o2max (r = −0.73), and V˙o2θ (r = 0.89). The pooled mean τV˙o2 from six superimposed tests agreed with the arithmetic grand mean of the six tests.
Conclusions: The average of on-τV˙o2 and off-τV˙o2 fell within the 95% confidence interval of the pooled mean by the second test. Ramp-τV˙o2 was longer and less reproducible. These findings support the use of both on- and off-transit data for the determination of τV˙o2, an approach that reduces the number of transitions necessary for accurate determination of τV˙o2, potentially enhancing its clinical application.
