When running, many runners often focus on external factors such as shoes, apparel, or energy gels. Breathing, a direct link between the muscular and nervous systems, is frequently left to instinct. In reality, during the latter half of a long-distance race, how you control the airflow in and out of your lungs will determine success or failure.

The ability to maintain breathing rhythm at the end of a race determines whether a runner will break away or become exhausted. Photo: VnExpress Marathon.

When lungs "compete" for blood with legs

The most common mistake for new runners is shallow, rapid chest breathing. When the heart rate increases, shoulders rise, and air circulates only in the upper part of the lungs, while the bottom of the lungs – where most capillaries for gas exchange are concentrated – is deprived of oxygen.

As a result, the body quickly switches to an anaerobic state, increasing lactic acid buildup and causing muscle fatigue even without accelerating. A 2022 study by Harbour et al., published in Frontiers in Physiology, also revealed a more severe mechanism called the "blood steal" phenomenon.

Specifically, when respiratory muscles are overloaded due to incorrect breathing, the body activates a survival mechanism, prioritizing blood flow to the lungs and diverting blood away from the limb muscles. This is the scientific explanation for why, in the final kilometers, a runner's legs can feel heavy as lead, even when their will pushes them forward.

Breathing techniques to reduce energy expenditure

To prevent this, runners need to switch to diaphragmatic breathing (belly breathing). When inhaling, the diaphragm lowers, causing the abdomen to expand, maximizing oxygen intake. When exhaling, residual air is thoroughly expelled.

Harbour's research team affirmed that belly breathing reduces the energy consumed for respiration, preventing the "chest tightness" sensation when fatigued.

To optimize performance, many advanced runners adopt a technique of synchronizing their breathing with their stride. A 2025 synthesis of studies by Bernhart et al. showed that this synchronization significantly reduces the load on respiratory muscles.

Synchronizing breathing with strides helps reduce hip impact and conserves energy. Photo: VnExpress Marathon.

Accordingly, a 3:2 rhythm (three steps inhaling, two steps exhaling) is recommended for easy runs. This odd rhythm allows runners to alternate which foot lands during exhalation, thereby distributing the load and reducing the risk of hip impact. Conversely, for faster running, a 2:2 rhythm is more suitable to meet the body's increased oxygen demand.

Don't overthink nose versus mouth breathing

Many runners wonder whether to breathe through their nose or mouth while running, but science indicates this isn't a decisive factor for endurance.

Nasal breathing helps warm and humidify the air and stimulates the production of nitric oxide (NO), a substance that promotes vasodilation and blood circulation. Therefore, nose breathing is an ideal choice for low-intensity recovery runs.

However, during races or high-intensity training, mouth breathing is essential to rapidly take in large amounts of oxygen. The key isn't the airway used, but the depth and rhythm of the airflow.

Use breath to master the mind

Breathing is not only a physiological tool but also a psychological lever for runners. When stressed or exhausted, the natural tendency is to try to inhale deeply. However, the paradox is that to take in new air, you must first expel all the old air.

Bernhart's 2025 research emphasizes the importance of actively extending exhalation. This action activates the parasympathetic nervous system, helping to lower heart rate and restore calm even during intense physical activity.

Like muscle training, breathing techniques need to be honed daily. Start practicing belly breathing while sitting at work or walking, and feel the 3:2 rhythm during slow runs. Once breathing becomes subconscious, you will find yourself running farther, more enduringly, and with greater ease.

Nguyen Ky