Adaptions to exercise.

[sandymere 8,263]

Ready for work.

 

At the beginning of the season many working dogs face a sharp increase in their exercise demands which can lead to unnecessary injuries, illness and reduced performance. Previously I have advocated pre season exercise to prepare the muscloskeletal system to deal with this issue but there are also stresses put on the cardiovascular and cooling systems that play an equally important role. An understanding of these processes can help us prepare the animal and thereby minimize the negative effects whilst maximizing potential ability. This is an adaptive process based on stressors that can either stimulate adaptive change or, if overloaded, lead to physical deteriation and injury. A rest period through the summer is a good idea and allows recovery from exercise induced problems such as the often unnoticed gastric ulceration that is not uncommon in working dogs. Against this is the idea that training prior to commencing work can reduce the risk of other problems such as exertional rhabdomyolysis and overheating.

Energy usage creates heat and the more energy used the more heat that will be produced, many mammals use the evaporation of sweat to dissipate heat from the whole body but the dog is only really able to do this via the tongue and mouth lining. This extremely limited ability combined with the very high exercise capability of dog’s results in overheating being a major limiting factor to the dog and the resultant dangers a cause for concern for the owner. There are two other causes of overheating fever through illness and extremes of temperature as in a dog left in a hot car but these are separate from the exercise induced heat under discussion. High body temp commonly known as hyperthermia is unavoidable with exercise and can be tolerated for short periods, the normal temp for a dog is 38.0 to 38.6C but sled dogs are often recorded with temps of over 40.0C during races. This type of hyperthermia in an unconditioned dog would lead to serious illness but through exercise adaptation working dogs are able to tolerate it without major ill effects although the process of this adaptation remains unclear.

 

The adaptation to deal with greater body heat does not mean that fit dogs cannot become dangerously hyperthermic and the differences between normal and dangerous can a subtle. Standard reactions to an increasing body temperature are panting, slowing down stopping and an increase in tongue size and redness. Early symptoms of over heating are not always easy to spot but can include becoming unsteady with a lack of coordination with owners describing the animal as “not being able to run straight†or “stumbling†as it walks. If steps are not taken at this point then fits, shock and death are likely to follow. The first step if to reduce the amount of heat being produced by stopping the exercise and if caught in time there will be a natural drop in temp and recovery at least during the colder winter months. In more serious cases a simple cessation of exercise may not be enough and active cooling may be required, water to soak the dog or ice packs are useful but as dogs is not designed to lose heat through the skin as in sweating animals, they do not have the surface blood vessels, so it is less effective than in animals designed to lose heat this way. Any dog that has suffered these symptoms needs the attention of a vet as, even if seemingly recovered, serious complications can occurs hours after the episode. As good conditioning seems to protect working dogs from the effects of hyperthermia then pre season fitness is a key to preventing complications, a fit dog will still get hot but its body will have adapted to cope with the conditions to a much greater degree.

 

The next area of adaptation concerns the heart and blood transport or cardiovascular system. The heart is a muscle and like other muscles it responds to stressors in the form of exercise, the blood vessels carry the blood to the body taking supplies to the muscle and removing waste products and these like the heart adapt to exercise. The heart when appropriately exercised will grow in size giving bigger chambers to allow more blood to be pumped at each stroke whilst gaining muscle power to enable a stronger pumping action. A trained athlete be it dog or human would be expected to have a slower resting pulse than average just because of the increased efficiency that training brings. The normal heart rate of a dog would be around to 100 beats a minute but an extremely fit dog this could be below 60; this could be a sign of a heart problem in a normal dog but is an expected result in a fit one. Along with an increase to the available cardiac output there is also an increase in blood volume and the production of more of the small blood vessels, capillaries, that take blood to the muscles. Again the process of growth of these vessels is not well understood but the results are, more blood vessels bringing nutrients and taking away waste products from working muscles enables increased performance. Big muscles without the extra oxygen, fuel etc would not be effective for very long. Some dogs are born with larger than normal hearts, increased red cell counts and blood volumes, the greyhound being an example, but all dogs can through appropriate exercise regimes increase their cardiovascular abilities.

 

So in conclusion I would suggest a little pre season training is sensible preparation and should reduce the incidence of early season injuries and health problems. Bringing about functional, adaptive, changes to the whole system prepares the dog in readiness for the rigors of work and so reduces the adaptations that are required in the field. This can lead to a reduction in a variety of issues ranging from minor strains to overheating/hyperthermia, cardiac muscle damage and exertional rhabdomyolysis.

 

Regards Sandymere.