Stride length and respiratory tidal volume in exercising thoroughbred horses.

The research article examined how horses’ respiratory frequency and volume changed in response to running speed and metabolic demand, revealing that horses can adjust breath volume, but not frequency, independent of stride length under certain conditions.

Objective and Hypothesis

• The main aim of the study was to examine locomotor-respiratory coupling in horses. This is the relationship between the horse’s physical movement and their respiration.
• The researchers hypothesized that this coupling may be a mechanism enabling horses to match their lung ventilation (breathing rate and depth) with running speed and metabolic power. Thus, as a horse’s speed or metabolism increases, its breathing adjusts to maintain efficient oxygen exchange and energy use.

Methodology

• To test this hypothesis, the effect on respiratory frequency (how often a horse breathes) and tidal volume (how deep a horse breathes) in thoroughbred horses was tested under varying circumstances. Running speed was changed, but metabolic demand was kept constant by adjusting the incline of the treadmill on which the horse was running.
• This procedure was performed at three different speeds and at two different levels of metabolic rate.

Findings

• The findings suggest horses can control their tidal volume – how deeply they breathe – independently of their stride length, but not their respiratory frequency or how often they breathe.
• This indicates that horses can modify the depth of their breathing based on internal metabolic requirements even when maintaining a certain pace or stride length. This level of control enables efficient oxygen use and energy expenditure.
• However, when running on a treadmill set at 0 degrees incline, horses likely do not increase their tidal volume. The researchers suggest this is due to the extra energy cost that taking larger breaths would entail.