Exercise intensity is often prescribed using age-based heart-rate formulas or estimated training zones. However, everyone’s physiology is different. Measuring your individual training thresholds allows exercise intensity to be prescribed based on your own physiology.
Why do training thresholds matter?
As exercise intensity increases, your body’s energy demands rise, resulting in predictable changes in metabolism and breathing. Two important physiological thresholds help identify these changes.
These thresholds divide exercise into broad intensity domains. Below the first threshold, the body can reach a relatively steady response and exercise is usually sustainable for a prolonged period. Between the first and second thresholds, breathing and metabolic demand rise but a steady state may still be achieved. Above the second threshold, disturbance accumulates more rapidly and the effort can only be sustained for a comparatively short time.
Knowing where these transitions occur can be more useful than relying only on a percentage of predicted maximum heart rate. Two people of the same age can reach their thresholds at different heart rates, speeds or workloads because of differences in fitness, health, medication, training history and individual physiology.
Aerobic threshold
The aerobic threshold (AeT) is the exercise intensity where your body is able to comfortably meet its energy demands predominantly through aerobic metabolism. It is commonly associated with the first ventilatory threshold, or VT1, during a respiratory-gas exercise test.
At or below your aerobic threshold:
- Breathing remains relatively comfortable and controlled.
- Exercise can usually be sustained comfortably for a prolonged period.
- Your body produces energy predominantly through aerobic metabolism, using a combination of fat and carbohydrate.
Training around your aerobic threshold can help:
- Build aerobic endurance.
- Improve cardiovascular fitness.
- Increase the workload or pace that can be sustained comfortably.
- Delay fatigue during prolonged exercise.
Is the aerobic threshold the same as Zone 2?
Exercise at or below the aerobic threshold often corresponds to what is commonly called Zone 2 training. However, the terms are not automatically identical. There are several three-zone and five-zone systems in common use, and watches, gyms, coaches and laboratories may define the boundaries differently.
In a physiology-based model, Zone 2 may refer to exercise below or close to the first threshold. In some commercial five-zone systems, the same label may be calculated from a percentage of estimated maximum heart rate instead. The numerical zone can therefore differ even though the label is the same.
A measured threshold provides an individual reference point. Heart rate, pace, treadmill speed, cycling power and perceived effort can then be considered together to translate the laboratory result into practical training.
Anaerobic threshold
The anaerobic threshold (AT) is commonly used to describe a higher exercise intensity where blood lactate begins to rise more rapidly because production exceeds the body’s ability to clear and use it at the same rate. During respiratory-gas testing, a related change may be identified as the second ventilatory threshold, or VT2.
Above this threshold:
- Breathing becomes noticeably heavier and more difficult to control.
- Lactate and other metabolic disturbances accumulate more rapidly.
- Fatigue develops quickly.
- Exercise can only be sustained for a relatively short period.
Training around your anaerobic threshold can help:
- Improve sustainable higher-intensity exercise capacity.
- Guide interval and higher-intensity training.
- Monitor improvements in endurance performance.
- Track meaningful changes in fitness, even when VO₂ max changes only modestly.
Threshold terminology is not perfectly standardised
“Aerobic threshold”, “anaerobic threshold”, “lactate threshold”, “gas-exchange threshold”, VT1 and VT2 are sometimes used as though they are interchangeable. They describe related physiological transitions, but they are not necessarily the same measurement.
Lactate thresholds are identified from blood-lactate measurements. Ventilatory thresholds are identified from changes in oxygen consumption, carbon-dioxide production and ventilation during a graded exercise test. The results often occur in a similar region, but the method, protocol and interpretation can affect the precise point identified.
For this reason, a threshold result should be interpreted in the context of the testing method used rather than treated as an absolute boundary that never changes.
How are ventilatory thresholds measured?
At Executive Medicine, VO₂ max testing is performed during a graded treadmill exercise test. Intensity progressively increases while a specialised face mask measures the oxygen you consume and the carbon dioxide you produce. Heart rate, breathing, symptoms and exercise performance are monitored throughout the test.
As workload rises, the relationship between oxygen consumption, carbon-dioxide production and ventilation changes. These respiratory-gas responses can be used to identify the first and second ventilatory thresholds and to determine the corresponding heart rate and workload.
The mask-based test identifies ventilatory thresholds; it does not directly measure blood lactate unless separate blood sampling is also performed. A threshold is not always perfectly distinct, so the full pattern of results and the person’s physiological response need to be interpreted by an appropriately trained professional.
Why is this important for you?
Knowing your individual thresholds allows exercise intensity to be prescribed more precisely. This can help:
- Establish personalised heart-rate training zones.
- Guide endurance and interval training.
- Match exercise intensity to your health, fitness or performance goals.
- Monitor improvements in fitness over time.
- Reduce the risk of making every session too easy, too demanding or unnecessarily similar.
For someone building general health and aerobic capacity, the first threshold can help define a sustainable training range. For an endurance athlete, both thresholds can help distribute easier aerobic work, moderate sessions and higher-intensity intervals. When retesting shows that a threshold occurs at a faster speed or greater workload at a similar heart rate, this may represent a meaningful improvement even if VO₂ max has changed little.
Thresholds are guides, not fixed limits
Heart rate at a threshold can vary from day to day. Temperature, hydration, fatigue, recent exercise, stress, illness, medication and the mode of exercise can all influence the response. Treadmill and cycling thresholds may also differ.
A laboratory result is therefore best used as an informed starting point. Heart rate can be combined with breathing, perceived effort, pace or power, symptoms and recovery. Training zones may need to be adjusted as fitness or health changes.
Exercise testing and safety
Graded exercise testing and higher-intensity training are not appropriate for everyone without prior assessment. Seek medical advice if you have chest discomfort, unexplained breathlessness, fainting, palpitations, known cardiovascular or respiratory disease, significant cardiovascular risk factors, a recent illness or a marked change in exercise tolerance.
The bottom line
Understanding your training thresholds helps ensure you are exercising at the right intensity for your goals—allowing you to train smarter, not just harder. Measured thresholds can provide more individual guidance than age-based formulas, but they should be interpreted according to the testing method and applied alongside your broader health, symptoms and training response. Measure. Understand. Improve.
How Executive Medicine can help
Executive Medicine’s Premium Plus assessment includes VO₂ max testing as part of a broader doctor-led health assessment. The respiratory-gas response can help identify individual ventilatory thresholds and establish practical exercise training zones aligned with your health and goals.
References
- Balady GJ, Arena R, Sietsema K, et al. Clinician’s Guide to Cardiopulmonary Exercise Testing in Adults: A Scientific Statement From the American Heart Association. View source .
- Fletcher GF, Ades PA, Kligfield P, et al. Exercise Standards for Testing and Training: A Scientific Statement From the American Heart Association. View source .
- Poole DC, Rossiter HB, Brooks GA, Gladden LB. The Anaerobic Threshold: 50+ Years of Controversy. View source .
- Faude O, Kindermann W, Meyer T. Lactate Threshold Concepts: How Valid Are They?. View source .
