Submaximal Exercise Testing and Maximal Oxygen Uptake Assessment

Submaximal exercise testing encompasses a range of protocols in which individuals perform physical activity at intensities below their maximal capacity. These tests are designed to estimate cardiorespiratory fitness—most notably maximal oxygen uptake (VO2max)—without requiring exhaustive effort or specialised laboratory apparatus. Common submaximal protocols include step tests, cycle ergometry, treadmill walking or running at set speeds, and field-based walking tests. By recording physiological responses such as heart rate, workload and recovery kinetics during these exercises, predictive equations or modelling techniques can infer VO2max with acceptable precision. The benefits of submaximal methods include reduced risk, greater accessibility, lower cost and the capacity to track fitness over time in diverse populations. Maximal oxygen uptake remains the gold standard index of aerobic capacity and is inversely associated with cardiovascular and all-cause mortality. In practice, VO2max can be measured directly through cardiopulmonary exercise testing (CPET) or approximated indirectly via submaximal responses combined with demographic or anthropometric data. Advances in sensor technology and computational modelling have further enhanced the reliability and convenience of indirect assessments, enabling widespread application in clinical, occupational and athletic settings worldwide.

Research from Nature Portfolio

Recent studies have harnessed large population cohorts to develop predictive models for VO2max based solely on wearable sensor data. One investigation trained machine-learning algorithms on heart rate and step count streams gathered during routine activities to generate point estimates and confidence intervals for VO2max. Tested in thousands of healthy adults and validated against laboratory treadmill protocols, the model achieved an average error below five millilitres per kilogram per minute. By relying on data routinely collected by fitness trackers, this approach promises scalable, remote monitoring of aerobic fitness and personalised exercise feedback without additional burden on users or clinicians.

Submaximal Exercise Testing and Maximal Oxygen Uptake Assessment publication trend

The graph below shows the total number of articles in submaximal exercise testing and maximal oxygen uptake assessment across all publications each year (not limited to Nature Index journals).

Technical terms

Submaximal exercise test: An exercise protocol performed below maximal effort, used to estimate aerobic capacity indirectly.

Maximal oxygen uptake (VO2max): The highest rate at which oxygen can be taken up and utilised during intense exercise, expressed in mL·kg⁻¹·min⁻¹.

Cardiopulmonary exercise testing (CPET): A laboratory procedure measuring respiratory gases and cardiovascular responses during graded maximal exercise.

Step test: A submaximal protocol in which participants step onto and off a platform at a fixed cadence to elicit heart rate responses.

Heart rate recovery (HRR): The rate at which heart rate declines after exercise, reflecting autonomic function and fitness.

References

1. Estimation of cardiorespiratory fitness using heart rate and step count data. Scientific Reports (2023).
2. Smartwatch-Based Maximum Oxygen Consumption Measurement for Predicting Acute Mountain Sickness: Diagnostic Accuracy Evaluation Study. JMIR mHealth and uHealth (2023).
3. Assessment and repeatability of aerobic capacity using the Chester Step Test among current, former, and never smokers. Internal and Emergency Medicine (2024).
4. A Moderate Walking Test Predicts Survival in Women With Cardiovascular Disease. American Journal of Preventive Medicine (2023).