Cardiovascular and respiratory adaptations during effort are intended to ensure the oxygen supply and nutrients needed for muscular activity and to allow for the elimination of wastes, particularly carbonic gas and heat, produced by muscular metabolism. These adaptations are indispensable not only for the completion of the sporting test in good conditions, but also to continue effort beyond the first instants. Two types of responses of the organism can be distinguished:
|
– an immediate response adapted to the instantaneous needs of the organism, therefore concomitant with the effort
|
– a more long term response that anticipates the organism's needs and corresponds to the adaptations caused by the organism
|
During physical exercise
Changes in the circulatory function during work are primarily to increase the blood flow and thereby supply oxygen to the tissues that are experiencing increased metabolism, particularly the muscles. The organism reaches this state by increasing the heart rate and redistributing the blood mass to the zones of activity to the detriment of the zones that are at rest. These changes are accompanied by an increased capacity of the blood to carry oxygen due to a contraction of the spleen that allows a large number of red blood cells to be sent into the blood, thereby increasing the hematocrit and amount of hemoglobin.
|
The heart flow can increase considerably and reach ten times its level at rest. The frequency of heart beats increases very noticeably in relation to the intensity of the effort, it can reach 300 beats per minute in racing Greyhounds, and 200 in sled dogs. The working muscles are at the center of intense vasodilatation; dilating the blood vessels allows muscles to increase their internal blood flow. The breath rate evolves in several phases during effort:
|
– during the first three to four seconds, the breath rate increases dramatically
– a plateau is then reached that will be maintained until the end of the effort
– during the recuperation period, a low decrease in respiratory frequency will occur, going from more than 200 movements per minute to approximately 30.
|
Ventilatory changes during exercise.
|
From the beginning of exertion, ventilation increases rapidly, then a second phase of slower increase appears and exists until ventilation is stabilized at a plateau. Once work has stopped, ventilation suddenly decreases, then more slowly decreases to return to its normal rate at rest.
|
The effects of training
After daily training for 4 to 5 weeks, the dog's body will present significant modifications in its cardiovascular and respiratory systems. Cardiac Average amounts of VO2 max known in dogs and hemodynamic modifications due to repeated physical exercise tend to minimize the energy needed for cardiac work, as well as to develop the capacity for the heart to pump. In trained dogs, the heart rate at rest is lower than that for sedentary dogs and arrhythmia is more marked. Their plasmatic volume is increased and the return of venous blood is improved, which results in an overall increase in heart flow.
|
|
Intensive training sometimes leads to hypertrophy of the heart. In Greyhounds, for example, six months of intense training causes an increase of 50 percent of the thickness of the heart wall and an increase of 30 percent of the volume of the left ventricular cavity. Training will also cause an increase in the number and density of capillary blood vessels in muscle. Finally, contrary to popular belief, in dogs with good health, regular physical exercise brings no or little modification to the respiratory system. It is the body's overall capacity to consume oxygen that is considerably increased through endurance training (we speak of "VO2Max," the maximum consumption of oxygen). These changes can only take place optimally in dogs with good overall health. Any change or insufficiency of these functions will limit the possibilities for adapting to the conditions of effort and, as a result, also limit performance in sports or work.
|
|
