The effect of exercise on diaphragmatic activation in horses.

This research investigates the impact of exercise on the activation of the diaphragm in horses by using electromyographic electrodes. The findings suggest that biomechanical forces play a minor role in equine respiration during exercise and demonstrate that the diaphragm’s total electric activity and mechanical output increase in proportion to any exercise-induced heavy breathing.

Methodology

• The researchers conducted their study on horses that had been chronically instrumented with costal diaphragmatic electromyographic (EMG) electrodes. This allowed them to directly monitor the electrical activity of the diaphragm during exercise.
• The horses exercised without the restriction of a breathing mask. This setup ensured that the horses’ natural breathing patterns were not altered.
• Changes in esophageal (Pes), gastric (Pga), and transdiaphragmatic (Pdi) pressures were measured during exercise. These measurements were then correlated with the diaphragmatic EMG activity (denoted as CS EMG) and the impact from the left forelimb of the horses.

Results

• Throughout all observed breaths, a notable finding was that the CS EMG activity always coincided with a decrease in Pes.
• Upon increasing the intensity of exercises in all trials, there was a linear increase in the CS EMG activity, Pga and Pdi. Conversely, Pes decreased proportionately with the intensity of exercise.
• Regardless of the type of gaits employed, the frequency of strides (fS) and the frequency of breathing (fR) were observed to synchronise one for one. However, this consistent phase-coupling relationship between fR and fS was present only when the horses were cantering and galloping, but not while walking or trotting.

Conclusion

• The study concluded that the contribution of biomechanical forces to ventilation—that is, the horse’s breathing—is minimal during exercise.
• The diaphragm was found to be continuously active during each breath. This signal, called phasic activity, was an important finding of the research.
• The total electric activity and the mechanical output of the diaphragm were proportionate to exercise-induced heavy breathing, referred to here as exercise hyperpnea. This correlation suggests that exercise causes an increase in the diaphragm activity in response to the increased demand for oxygen.