VO₂Max and health

Japan's Ministry of Health, Labour and Welfare (MHLW), in its 2023 Physical Activity and Exercise Guide for Health Promotion, describes cardiorespiratory fitness as a strong predictor of mortality from various causes and disease incidence. Here we introduce the research behind that statement and its numerical findings.

What difference is associated with 1 MET higher fitness?

A review of 33 cohort studies of healthy adults (102,980 participants in the all-cause mortality analysis) found that each 1-MET higher level of fitness measured by exercise testing was associated with a relative risk of 0.87 for all-cause mortality (95% confidence interval 0.84–0.90) and 0.85 for coronary heart disease/cardiovascular events (0.82–0.88). These correspond to approximately 13% and 15% lower relative risks (Kodama et al., 2009).

A more recent review of 34 cohort studies found relative risks per 1-MET higher fitness of 0.88 for all-cause mortality (0.83–0.93), 0.87 for cardiovascular mortality (0.83–0.91), and 0.93 for cancer mortality (0.91–0.96). Comparing the highest with the lowest fitness groups, the relative risks were 0.47, 0.49 and 0.57, respectively (Han et al., 2022).

MHLW summarizes these results as approximately 10–20% lower relative risks of all-cause or cardiovascular mortality per 1-MET higher fitness. One MET corresponds to 3.5 mL/kg/min.

The low- and high-fitness groups used in the research

Kodama et al. adjusted for age and sex and standardized everyone's fitness to that of a 50-year-old man. On this scale, the low-fitness group was below 7.9 METs (approximately 27.7 mL/kg/min) and the high-fitness group was at least 10.9 METs (approximately 38.2 mL/kg/min). Compared with the high-fitness group, the low-fitness group had relative risks of 1.70 for all-cause mortality (1.51–1.92) and 1.56 for coronary heart disease/cardiovascular events (1.39–1.75). These results compare groups defined for the study.

You cannot apply these cut-offs directly to your measured value or smartwatch estimate to classify yourself as having low fitness or calculate your future risk. For Japanese reference values by sex and age, see MHLW's 2023 reference tables. These reference values are not individual diagnoses either.

Estimates without exercise testing

The two reviews above used fitness measured by exercise testing. A review of eight cohort studies involving more than 170,000 people also examined fitness estimated from age, resting heart rate, body characteristics and physical activity. For each 1-MET higher estimated fitness, hazard ratios were 0.83 for both cardiovascular mortality (0.80–0.86) and all-cause mortality (0.78–0.88). The association was linear and did not differ between men and women. However, predictive performance was reported to be slightly lower than for exercise-tested fitness (Qiu et al., 2021).

Even a small improvement

MHLW states that even a small improvement in cardiorespiratory fitness can be expected to provide substantial health benefits, across people with low through high fitness. However, associations between groups in observational studies do not establish that an individual's mortality risk will fall by a corresponding amount when their fitness improves.

See the comparison of exercise methods for ways to improve, or measurement guide to check your current level.