title: Selecting constant work rates for endurance testing in COPD: the role of the power-duration relationship.
abstract: Constant work rate (CWR) exercise testing is highly responsive to therapeutic interventions and reveals physiological and functional benefits. No consensus exists, however, regarding optimal methods for selecting the pre-intervention work rate. We postulate that a CWR whose tolerated duration (tlim) is 6 minutes (WR6) may provide a useful interventional study baseline. WR6 can be extracted from the power-duration relationship, but requires 4 CWR tests. We sought to develop prediction algorithms for easier WR6 identification using backward stepwise linear regression, one in 69 COPD patients (FEV1 45 ± 15% pred) and another in 30 healthy subjects (HLTH), in whom cycle ergometer ramp incremental (RI) and CWR tests with tlim of ∼6 minutes had been performed. Demographics, pulmonary function, and RI responses were used as predictors. We validated these algorithms against power-duration measurements in 27 COPD and 30 HLTH (critical power 43 ± 18W and 231 ± 43W; curvature constant 5.1 ± 2.7 kJ and 18.5 ± 3.1 kJ, respectively). This analysis revealed that, on average, only corrected peak work rate ( = WRpeak-1 min × WRslope) in RI was required to predict WR6 (COPD SEE = 5.0W; HLTH SEE = 5.6W; R(2) > 0.96; p < 0.001). In the validation set, predicted and actual WR6 were strongly correlated (COPD R(2) = 0.937; HLTH 0.978; p < 0.001). However, in COPD, unlike in HLTH, there was a wide range of tlim values at predicted WR6: COPD 8.3 ± 4.1 min (range 3.6 to 22.2 min), and HLTH 5.5 ± 0.7 min (range 3.9 to 7.0 min). This analysis indicates that corrected WRpeak in an incremental test can yield an acceptable basis for calculating endurance testing work rate in HLTH, but not in COPD patients.
authors.affiliation: 1Department of Pulmonology, University Medical Center Groningen, Groningen, Netherlands.
authors.forename: Hester
authors.initials: H
authors.lastname: van der Vaart
authors.forename: Scott R
authors.initials: SR
authors.lastname: Murgatroyd
authors.forename: Harry B
authors.initials: HB
authors.lastname: Rossiter
authors.forename: Carey
authors.initials: C
authors.lastname: Chen
authors.forename: Richard
authors.initials: R
authors.lastname: Casaburi
authors.forename: Janos
authors.initials: J
authors.lastname: Porszasz
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000465:Algorithms; D016022:Case-Control Studies; D005080:Exercise Test / Q000379:methods*; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology*; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology*; D012123:Pulmonary Ventilation; D013997:Time Factors; D055815:Young Adult
keywords: Exercise; critical power; gas exchange; ventilation