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Normative reference equations for leg discomfort during incremental cardiopulmonary cycle exercise testing in older
Rachelle Aucoin1, Dennis Jensen2,3, Michael Stickland4
1Respiratory Epidemiology Team, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada.
Background:
Leg discomfort, assessed with the Borg category-ratio 0-10 (Borg CR10) scale, is a primary reason for exercise cessation in both health and disease. However, interpretation during cardiopulmonary exercise testing (CPET) is limited by the absence of normative reference equations.
Purpose:
Develop normative reference equations for leg discomfort during CPET in relation to absolute and relative power output (W) and rate of oxygen uptake (V'O2).
Methods:
This was a retrospective analysis of the Canadian Cohort Obstructive Lung Disease (CanCOLD) study. We included healthy males and females aged ≥40 years who completed symptom limited incremental cycle CPET. The probability of each Borg CR10 leg discomfort rating by W or V'O2 was predicted using multinomial logistic regression. Model performance was evaluated by fit, calibration, discrimination (c-statistic), and externally validated in an independent sample (n = 86) of healthy Canadian adults.
Results:
In total, 156 participants (43% female) were included (mean age 64.8 years). The models demonstrated good discrimination in both internal and external validation (AUC 0.85-0.90), with similar performance across absolute and relative W and V'O2. An upper limit of normal ([ULN]; 95th percentile) could not be defined, as leg discomfort responses were highly clustered within the predicted normal range across exercise intensities.
Conclusions:
We present normative reference equations for leg discomfort during CPET. Although an ULN could not be established, these models enable grading and interpretation of leg discomfort relative to the predicted normal responses and facilitate comparisons across individuals and groups in both clinical and research settings.
