Higher VO2 Max Went With Lower Death Risk in Heart Failure
Each extra mL/kg/min of peak VO2 went with about 14% lower all-cause mortality. Heart-related death alone did not reach significance.
Evidence rating for the proposition “Higher cardiorespiratory fitness predicts lower all-cause mortality risk”: Established
Yes for death from any cause, less clearly for heart-related death. A meta-analysis of 64 observational studies in heart failure found each 1 mL/kg/min higher peak VO2 went with a hazard ratio of 0.86 for all-cause mortality (95% CI 0.82 to 0.90). For cardiovascular mortality alone it was 0.92 (0.82 to 1.02), not significant. Heterogeneity was high and publication bias was evident. These are lab-measured values in patients, not wearable estimates.
Does peak VO2 predict death in heart failure?
For all-cause death, yes. A 2025 meta-analysis pooled 64 observational studies in patients with heart failure. Per 1 mL/kg/min increase in peak VO2, all-cause mortality had a hazard ratio of 0.86 (95% CI 0.82 to 0.90).
The combined outcome of ventricular assist device, transplant or death had a hazard ratio of 0.84 (0.79 to 0.89).
Peak VO2 is measured in a lab during a maximal exercise test. The authors call it a prognostic marker for several causes of mortality and hospitalization.
1 study
- In 64 observational studies of heart failure, each 1 mL/kg/min higher peak VO2 was associated with a hazard ratio of 0.86 (95% CI 0.82 to 0.90) for all-cause mortality and 0.84 (0.79 to 0.89) for ventricular assist device, transplant or all-cause mortality, but 0.92 (0.82 to 1.02) for cardiovascular mortality.
Why is the heart-specific result not significant?
The abstract does not say. The hazard ratio for cardiovascular mortality was 0.92 (95% CI 0.82 to 1.02, P = 0.12), a smaller gradient with an interval that crosses 1.
That differs from the all-cause result. The authors report variation among studies by age, sex, body mass index, ejection fraction, atrial fibrillation, hypertension, chronic kidney disease, diabetes and treatment. Heterogeneity for all-cause mortality was 85%. They also report a significant risk of publication bias.
So the pooled estimate is real but soft. It describes an average across different patients and study designs.
Is the link the same in people without heart failure?
It points the same way. A meta-analysis of 33 studies in healthy people found a relative risk of 0.87 for all-cause mortality per 1-MET higher fitness (0.84 to 0.90). Low-fitness participants had a relative risk of 1.70 against high-fitness participants.
In 6,213 men referred for treadmill testing, each 1-MET higher capacity gave a 12% improvement in survival. Peak exercise capacity was the strongest predictor of death among both healthy men and those with cardiovascular disease.
The units differ. One MET is 3.5 mL/kg/min. As rough arithmetic, a hazard ratio of 0.86 per mL/kg/min compounds to about 0.59 per MET. That is a conversion across studies with different patients, not a finding.
2 studies
- In 33 studies of healthy men and women, the relative risk of all-cause mortality per 1-MET higher fitness was 0.87 (95% CI 0.84 to 0.90), and low-fitness participants had a relative risk of 1.70 (1.51 to 1.92) against high-fitness participants.
- In 6,213 men referred for treadmill testing, with and without cardiovascular disease, each 1-MET increase in exercise capacity conferred a 12% improvement in survival, and peak capacity was the strongest predictor of death.
Does exercise training change the outcome?
Modestly, and not clearly. HF-ACTION randomized 2,331 outpatients with heart failure and reduced ejection fraction to supervised exercise training plus usual care or usual care alone. Median follow-up was 30 months.
In the primary analysis, death or hospitalization occurred in 65% against 68% (hazard ratio 0.93, 95% CI 0.84 to 1.02). All-cause mortality was 16% against 17% (0.96, 0.79 to 1.17). Neither was significant. Adherence fell from 95 to 74 minutes a week.
After adjusting for prognostic baseline factors, the hazard ratio for death or hospitalization was 0.89 (0.81 to 0.99). The authors describe modest significant reductions after adjustment.
This trial tested exercise training, not a VO2 change directly.
1 study
- In 2,331 outpatients with heart failure and reduced ejection fraction followed for a median of 30 months, exercise training gave a hazard ratio of 0.93 (95% CI 0.84 to 1.02) for death or hospitalization in the primary analysis and 0.89 (0.81 to 0.99) after adjustment for prognostic baseline factors.
Does a watch measure this number?
No. The heart failure figures come from laboratory tests on patients. A watch's VO2 max is an estimate, and validation studies found errors of 7% to 16% in healthy adults. See how VO2 max is calculated and how far watches miss. Healthy-population evidence is in VO2 max and longevity.
No study here tests a watch estimate in people with heart failure.
What does this not settle?
The pooled analysis describes an association in observational studies. It does not show that raising peak VO2 lowers mortality. It combines different heart failure types, ejection fractions and treatments.
HF-ACTION tested exercise training and reported mixed results by analysis. No source here shows what a given person's peak VO2 predicts.
The heart failure figures are associations from observational studies with high heterogeneity and publication bias, using lab-measured peak VO2. They do not show that raising VO2 lowers mortality, and none tests a watch estimate in patients with heart failure.
Common questions
Does VO2 max predict death in heart failure?
For all-cause death, yes in a 64-study meta-analysis. Each 1 mL/kg/min higher peak VO2 had a hazard ratio of 0.86 (95% CI 0.82 to 0.90). For cardiovascular mortality alone it was 0.92 (0.82 to 1.02), not significant.
Is the result reliable?
It is soft. Heterogeneity for all-cause mortality was 85%, the studies varied by age, sex, ejection fraction and treatment, and publication bias was evident.
Does exercise training reduce deaths in heart failure?
In HF-ACTION with 2,331 patients, the primary analysis was not significant (hazard ratio 0.93 for death or hospitalization, 95% CI 0.84 to 1.02). After adjustment it was 0.89 (0.81 to 0.99).
Is the link the same in healthy people?
It points the same way. In 33 studies of healthy people, each 1-MET higher fitness went with a relative risk of 0.87 for all-cause mortality.
Can a smartwatch VO2 max be used in heart failure?
Not established. Heart failure evidence uses lab-measured peak VO2, and watch estimates missed lab values by 7% to 16% in healthy adults.
Sources
- Prognostic impact of peak oxygen consumption in heart failure: A systematic review and meta-analysis.
- Cardiorespiratory Fitness as a Quantitative Predictor of All-Cause Mortality and Cardiovascular Events in Healthy Men and Women
- Exercise capacity and mortality among men referred for exercise testing.
- Efficacy and Safety of Exercise Training in Patients With Chronic Heart Failure