Endurance riding has evolved dramatically over the past 25 years. Speeds have increased significantly, with horses now covering long distances at faster paces than ever before. As demands rise, so too does the importance of understanding the physiological systems that support performance, particularly the respiratory system.
Traditionally, when selecting an endurance horse, riders focus on cardiovascular recovery, conformation and soundness. The respiratory system is rarely top of the list. However, as speeds increase and the intensity of work changes, breathing may play a more important role than previously assumed.
Why breathing matters more at higher speeds?
At lower speeds, such as trotting at around 13 km/h, the respiratory system is unlikely to limit performance. At this pace, breathing and stride are not synchronised, and the horse moves approximately 700 litres of air in and out of the lungs per minute.
However, at higher speeds, for example, cantering at 26 km/h, the situation changes considerably. At this point:
- Airflow increases to approximately 1100-1300 litres per minute
- Breathing becomes synchronised with stride (one breath per stride)
- The energetic cost of breathing increases significantly
In fact, moving air in and out of the lungs at canter requires around 50% more energy per litre than at trot. This means that any factor that increases airway resistance may have a disproportionate effect on performance as speed increases.
The Upper Airway: a key site of resistance
A large proportion of resistance to airflow occurs in the upper airway including the nostrils, nasal passages and larynx (throat). Horses are obligate nasal breathers, meaning all airflow must pass through the nose.
At higher speeds, during inspiration (breathing in), negative pressure within the airways increases (becomes even more negative), which can lead to narrowing or partial collapse of the upper airway structures. This increases resistance and makes breathing more energetically costly.
Reducing airway resistance, even slightly, may therefore improve airflow efficiency particularly at canter and or gallop where breathing is tightly linked to stride.
Respiratory Health: often overlooked
In a healthy endurance horse, the respiratory system is unlikely to be the primary limiting factor. However, even mild respiratory disease has been shown to negatively affect performance.
Importantly:
- Horses may have respiratory disease without obvious clinical signs
- Absence of coughing does not guarantee respiratory health
- Endoscopy is often required to detect undiagnosed or unrecognised issues
Field observations have shown that even horses living outdoors and appearing clinically normal may have significant airway inflammation.
Inflammation of the upper airway or trachea, even without lung involvement, can still impair performance. As in humans, mild respiratory illness may not prevent exercise, but it can reduce efficiency and willingness to perform.
Breathing, Heat and Energy balance
Endurance exercise generates substantial heat. Without effective cooling, a horse’s body temperature would rise rapidly. While sweating is the primary mechanism for heat loss, respiration contributes up to 15–25% of heat dissipation, depending on environmental conditions.
Efficient airflow is therefore not only important for oxygen delivery, but also for thermoregulation.
EIPH and the Changing Demands of Endurance
Exercise-induced pulmonary haemorrhage (EIPH), or “bleeding”, has traditionally been associated with racehorses. However, it is now recognised across a wide range of equestrian disciplines.
As endurance speeds increase, the risk of increased EIPH (microscopic lung vessel rupture) also rises. Studies have shown that lung changes associated with bleeding can occur at speeds of trot and above which are now commonly reached in endurance competition.
Recent research has confirmed that EIPH does occur to some extent in all endurance horses, suggesting that respiratory stress may be greater than previously assumed.
What does this mean for performance?
As endurance riding continues to evolve, it is likely that the respiratory system will play an increasingly important role in performance, particularly at canter and during more demanding sections such as climbs.
Key considerations include:
- The link between breathing and stride at canter
- The energetic cost of moving air at high airflow rates
- The impact of upper airway resistance
- The role of breathing in heat dissipation
- The potential for subclinical respiratory disease to be present and reduce performance
- The evidence that EIPH occurs in endurance horses
Small improvements in airflow efficiency may translate into meaningful benefits when horses are asked to compete at moderate speeds for hours or more.
Key takeaways
- Endurance speeds have increased, placing greater demands on the respiratory system
- At canter, breathing is synchronised with stride, increasing the importance of airflow efficiency
- The upper airway is a major contributor to airflow resistance
- Horses can have respiratory disease without obvious clinical signs
- Breathing plays a central role in both performance and thermoregulation
- EIPH occurs in endurance horses
- Reducing airway resistance may help support performance, particularly under high-intensity conditions
