Background: Older women are underrepresented in cardiac rehabilitation (CR) research despite high cardiovascular morbidity and unique functional limitations that influence exercise tolerance and outcomes. Determination of oxygen uptake (VO2) during walk testing and during recovery (VO2 kinetics) is critical for elucidating the pathophysiology of exercise intolerance observed in walk tests, quantifying physiological benefits derived from CR, and has been linked to prognosis and survival. As such, measuring VO2 during ambulatory testing offers practical utility for individualized exercise prescription, monitoring intervention response, and risk stratification.
Purpose: Demonstrate the novel use of VO2-measured walk testing to characterize aerobic function and exercise recovery dynamics in older females undergoing CR and develop prediction models for a large patient cohort.
Methods: We prospectively measured six‑minute walk distance (6MWD) with simultaneous ambulatory VO2 in older female inpatients undergoing intensive CR (August 2025-February 2026). Exercise VO2 was taken as the highest 30‑s average and VO2 recovery kinetics (time to 63% recovery) determined by non‑linear curve fitting. Using direct‑entry linear regression, we developed prediction models for walk‑test VO2 (predictors: 6MWD, height) and VO2 recovery kinetics (predictor: 6MWD), then applied the models to a retrospective cohort of older female inpatients who underwent CR between December 2022 and June 2024. We used these data to evaluate the effects of CR on derived exercise VO2 and VO2 recovery kinetics.
Results: Ten older females (mean age ± SD, 69 ± 8 years) completed admission 6MWD with ambulatory VO2 during inpatient CR. 6MWD was 419 ± 104 m, measured exercise VO2 15.9 ± 2.7 ml/kg/min, and measured VO2 recovery kinetics 74 ± 16 s. Regression models derived were 1) exercise VO2 = 45.857 + (0.006 × 6MWD) + (0.36 × height) (P = 0.028, R2 = 0.64), and 2) VO2 recovery kinetics = 120.675 – (0.113 × 6MWD) (P = 0.017, R2 = 0.53). Applied to a retrospective cohort of 192 older female inpatients (mean age 67 ± 12 years) with mixed cardiac indications, in whom 6MWD increased from 316 ± 129 to 459 ± 122 m (P < 0.001), estimated exercise VO2 increased from 15.2 ± 2.9 to 16.0 ± 2.9 ml/kg/min (P = 0.006), and estimated VO2 recovery kinetics improved from 87 ± 17 to 72 ± 18 s (P < 0.001).
Conclusions: The increased exercise VO2 with greater 6MWD reflects improved aerobic capacity and exercise tolerance, likely from enhanced cardiac output and peripheral muscle oxidative function. The faster post‑exercise VO2 recovery kinetics indicate improved autonomic and metabolic recovery, consistent with better cardiovascular control and reduced exercise intolerance. VO2 measurement during walk testing is a practical method to characterize aerobic function and recovery dynamics and clarify mechanisms of rehabilitation benefit. This may help inform individualized exercise prescription.