Aucoin R; Dalhousie University, Halifax, Nova Scotia, Canada.
Jensen D; Stickland M; Brotto A et al

Clinical Physiology & Functional Imaging. 46(4):e70083, 2026 Jul.

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.