Lack of stamina may be evidenced by a slower pace while riding or driving, resisting forward movement, abnormally heavy or rapid breathing during or after work and/or excessive sweating during or after work.

Disease or illness that affect any body system can decrease stamina. Tying-up, lameness, poor saddle fit and dozens of other conditions can be confused with or contribute to an apparent lack of stamina. Behavioral factors may overlap with physical factors, complicating the picture even more. In some cases, lack of training or rider ability are confused with a horse's lack of stamina.

The most common reason for a horse to be exercise intolerant is lack of cardiovascular fitness. Optimal conditioning requires consistent exercise. Heart and respiratory rates should return to normal fairly quickly following exercise. How quickly these return to normal following intense exercise is an indication of physical fitness.