Most content on energy pathways in sports is limited to a “with oxygen / without oxygen” table. This simplified division masks a rarely discussed point: the boundary between aerobic and anaerobic is not a switch. Both systems coexist continuously, and their respective contributions vary depending on the intensity, duration, and training level of the practitioner.
Understanding this mechanism allows for structuring workouts with more precision than the simple opposition of “cardio versus strength.”
Energy pathways in sports: why the aerobic-anaerobic boundary is blurry
The body never completely switches from one system to the other. During a moderate-paced jog, the aerobic metabolism dominates, but a fraction of energy already comes from anaerobic pathways. Conversely, a sprint lasting a few seconds primarily mobilizes phosphocreatine reserves (anaerobic alactic), while gradually engaging the aerobic system as the effort exceeds ten seconds.
INS Québec has updated its sports science glossary to distinguish between aerobic capacity (the maximum ability to use oxygen to produce energy) and cardiorespiratory fitness (a more global measure used in epidemiology and general physical condition). This distinction changes the way progress is assessed: a VO₂max test provides information on aerobic capacity, while a six-minute walk test measures cardiorespiratory fitness.
To delve deeper into aerobic and anaerobic activity in sports, one must go beyond the binary model and think in terms of the relative contribution of each pathway depending on the type of effort.
Intensity thresholds and lactate: concrete markers to differentiate aerobic and anaerobic
The most commonly used physiological marker to locate the switch between aerobic dominance and anaerobic dominance remains the lactate threshold. Below this threshold, the body eliminates the lactate produced as quickly as it generates it. Above this threshold, accumulation exceeds the elimination capacity, and fatigue sets in more quickly.
In practice, this threshold varies in intensity from one individual to another. A beginner runner may reach their lactate threshold at a much lower heart rate than a trained athlete. It is precisely this variability that makes standardized heart rate zones (the famous “zones 1 to 5”) approximate if they are not individually calibrated.
Three markers to gauge effort
- The conversation test: if you can speak in complete sentences without marked breathlessness, the effort is primarily aerobic. As soon as speech becomes fragmented, the anaerobic contribution significantly increases.
- Perceived exertion (Borg scale): a score of 4-5 out of 10 generally corresponds to an aerobic zone. Beyond 7, the anaerobic pathway significantly takes over.
- Duration of effort: an effort sustainable for more than three minutes primarily engages the aerobic system. Below thirty seconds at maximum intensity, the anaerobic alactic pathway dominates.
Field reports vary on the reliability of wrist-based optical heart rate sensors to estimate these thresholds. A heart rate monitor with a chest strap remains more accurate for anyone looking to calibrate their training zones.
Combining aerobic and anaerobic: what data shows about longevity
Competing articles present the benefits of each pathway separately. Recent cohort data tells a different story. A study published in the British Journal of Sports Medicine, reported by Futura Santé, followed about 150,000 people over three decades. The result: individuals combining resistance training (engaging the anaerobic pathway) and activity in the aerobic zone have the lowest mortality risks, up to 45% lower than those who are inactive.
This figure does not mean one must run a marathon and lift heavy weights every week. It indicates that the complementarity between the two pathways produces a protective effect greater than the exclusive practice of one or the other. A program that alternates moderate endurance sessions with short high-intensity sessions ticks both boxes.
Practical application based on goals
For a practitioner aiming for fat loss, moderate-intensity aerobic work burns lipids during the effort, while anaerobic sessions (short intervals, strength training) increase post-exercise calorie expenditure. One without the other yields slower results.
For an athlete seeking endurance performance (trail running, cycling, long-distance swimming), neglecting anaerobic work means hitting a plateau. Threshold or short interval sessions improve lactate tolerance and push the tipping point towards anaerobic. The result: a higher cruising speed in the aerobic zone.
VO₂max and anaerobic power: measuring progress in each pathway
Progress requires measurement. For the aerobic pathway, VO₂max remains the reference indicator. It represents the maximum volume of oxygen that the body can consume per minute. Some recent publications highlight that VO₂max is also a predictor of longevity, beyond its athletic use.
For the anaerobic pathway, the most common indicator is the maximum power developed during a short effort (Wingate test on an ergocycle, for example). This test measures the ability to produce energy without sufficient oxygen supply.
The available data do not allow for concluding that a single indicator is sufficient to assess overall physical condition. A high VO₂max does not indicate anything about anaerobic power, and vice versa. A comprehensive assessment combines both measures.
- Recommended frequency for the VO₂max test to track progress: every two to three months during the loading phase.
- The Wingate test (thirty seconds at maximum effort) provides a reliable insight into anaerobic power but requires a calibrated ergocycle.
- Smartwatches estimate VO₂max using algorithms, with a margin of error that varies by model and sensor positioning.
Differentiating between aerobic and anaerobic activity is not just about classifying sports into two columns. It is a matter of personal calibration, based on individual physiological thresholds and measurable indicators. Progress involves training both pathways, tailored according to the goal and adjusted through regular testing.