Anaerobic threshold. (a) Mann–Whitney U comparison of mean (95% CI) for CPET stratified and subsequently operated patients (13.3 ml/kg/min, 95% CI: 12.5 to 14.2) with those managed conservatively (9.2 ml/kg/min, 95% CI: 7.2 to 10.9;*** P < 0.001). The dashed line delineates the evidence-based threshold of 11.0 ml/kg/min. (b) Anaerobic threshold distributions for all CPET patients (n = 166, normal distribution on D’Agostino and Pearson omnibus normality test), CPET-era operated (n = 118, skewed distribution) and CPET conservatively managed subjects (n = 33, skewed distribution). Submaximal test results (no AT) have been removed from this analysis. AT: anaerobic threshold; CPET: cardiopulmonary exercise testing; Rx: management/treatment.