1.6.2 The long-term effects of exercise
The long-term effects of exercise have not been as well studied as the short4erm changes, but a number of adaptations have been observed. Prolonged exercise training leads to eccentric hypertrophy of the LV (and presumably the RV), resulting in an increased stroke volume. The maximum heart rate appears to be similar in trained and untrained animals; however, trained horses appear to be able to maintain stroke volume at high heart rates better than untrained animals, resulting in an increased performance capacity. The distribution of blood flow to skeletal muscles during exercise is assisted by an increase in the ramifications of blood vessels to fibre groups. This results in an increase in the maximal aerobic oxygen capacity of exercise-trained animals. Adaptation due to selective breeding has lead to a difference in the packed cell volume and oxygen carrying capacity of the 'hot blooded' breeds. Fit animals also appear to be able to move faster at the same maximal oxygen capacity. Athletic ability may also be related to the ability to tolerate increased levels of by-products such as lactic acid, which build up in the muscles during exercise, and affect anaerobic exercise capacity.