Answer:
The horses developed an oxygen debt when they exercise because they suffered from Exercise-Induced Pulmonary Hemorrhage (EIPH).
Explanation:
A temporary shortage of oxygen in the body tissues during physical exertion such as exercise or a sudden burst of activity is referred to as oxygen shortage.
Horses (compared to humans) are uniquely designed to experience little or none of this.
When the body takes up oxygen, it reacts with glucose to produce energy. This is called Aerobic respiration.
There is also another procedure that the body uses to produce energy. This occurs when glucose is broken down in the cells. After this happens, lactic acid is created but cannot be stored in the body and must be expelled.
This interval when energy is produced without the presence of oxygen is called "oxygen debt".
When a horse is fit, its breathing quickly returns to normal. The longer the time taken for the breathing to return to normal, the less fit the horse is.
One of the factors that can reduce the fitness of a horse is the Exercise-Induced Pulmonary Hemorrhage (EIPH).
This occurs when blood vessle in the lung ruptures causing blood to bleed into the airways. So blood occupies space where oxygen should have. This reduced the amount of oxygen delivered to the blood stream. Hence the oxygen debt takes longer to be repaid.
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