Ultra Canine Athletes Adapt Rapidly to Ongoing Intense Exercise

Super canine athletes seem to have an inborn ability to adapt rapidly to ongoing intense exercise unlike human marathon runners or triathletes who often need a full day of recovery. These optimally conditioned dogs have enormous aerobic capacity. Within four days after exercise begins, these dogs return to their pre-exercise health status despite sustained, strenuous exercise. Research by Michael Davis, D.V.M., Ph.D., DACVIM, professor of veterinary physiology at Oklahoma State Uni­ver­sity, has shown that during the first day of intense exercise, ultra canine athletes experience many of the metabolic changes seen in human endurance athletes. "These dogs undergo depletion of muscle energy reserves, increase in stress hormones, oxidative stress, and evidence of injury to protein, lipid and DNA just like humans," Davis says. "The major difference is that with subsequent consecutive days of exercise at the same intensity, these changes are reversed in dogs. Within four days, their metabolic profile returns to where it was before exercise began." Davis, who presented these findings last fall at the American Physiological Society's annual conference, says though it is a mystery what makes dogs premier performers, it is likely to have something to do with their ability to regulate extremely thin membranes in muscle fibers and changes in cells that are responsible for the body's energy production. "In the racing sled dogs we studied, we found that despite having to rely on muscle reserves during the first day of exercise, on subsequent days the dogs are able to use other sources of energy and even replenish their reserves, all while continuing to run 100 miles per day," says Davis. "They are undoubtedly one-of-a-kind athletes. Hopefully, we will learn from these dogs information that will benefit human performance as well." Obviously being fully trained and conditioned is important, too. "While untrained sled dogs have an average aerobic capacity of 175 ml/kg/min VO2 max — the ratio of volume of oxygen to body weight per minute — the aerobic capacity of fully conditioned sled dogs may be twice that amount," he says. Gastric Ulcers in Racing Sled Dogs Davis began studying the physiological aspects of racing sled dogs around 2000. Much of the research has evaluated the gastrointestinal disease that occurs in these dogs, as compared with ultra human athletes, with a goal of developing medications and treatments to help prevent exercise-induced stomach problems. The research has been published in articles in the Journal of Veterinary Internal Medicine. "We found that both people and canine athletes have a high incidence of gastrointestinal disease compared to the sedentary population," Davis says. "The reported prevalence of gastrointestinal disease in human athletes ranges from 30 to 40 percent of French marathon runners and triathletes to as high as 100 percent of Korean long-distance runners. Our initial surveillance study of racers found that nearly half experience gastritis, gastric ulcers or both." Why super athletes suffer from gastric erosion, bleeding and diarrhea is unknown, but these problems seem to occur regardless of exercise conditioning, diet or lifestyle. This led Davis and his team to deduct that a common feature of exercise is a predisposition to gastrointestinal dysfunction. "We went to Alaska and began scoping (gastroscopy) the stomachs of these dogs to assess whether they experienced any gastrointestinal effects from their sport," he says. "All the dogs we studied appeared normal and healthy. These dogs compete at the highest level and are capable of exercising at about 50 percent of VO2 max for up to 14 days with very few adverse effects." To diagnose a gastric ulcer, the veterinarians performed a gastroscopy, a procedure that enables them to insert a flexible scope down the esophagus into the stomach. The scope has a camera on the end that provides a view of the stomach walls. Ulcers appear as breaks in the lining of the stomach. When they are severe, bleeding can be seen. More commonly, lesions appear as areas of inflammation under the lining or partial thickness erosions. Not surprisingly, the researchers found that "from 40 to 60 percent of the dogs had abnormal stomachs," says Davis. "About 10 percent had true ulcers, although none showed outward signs of ulcers. Dogs generally don't until the condition is severe and requires intensive care." Signs of gastric ulcers include vomiting blood, abdominal pain and depression. Davis notes that as a routine, in both races and research studies, any dog showing signs of an ulcer would be withdrawn and properly treated. The researchers' hypothesis was that the prevalence and magnitude of the ulcers would increase as dogs continued to race. They speculated that stomach ulcers were unique to dogs that exercised for five or six consecutive days and was related to the effect of hard exercise. "In 2004, we conducted a study to confirm this, but found in sequential 100-mile runs, a dog remains static after the first hundred miles and dsn't get better or worse," Davis says. "We also found the percentage of affected dogs stays consistent. Keep in mind, 100 miles a day for these dogs is basically a trotting pace." More recently, the researchers have begun studying exercise-induced stomach ulcers in other canine athletes to determine whether they, too, are affected. "The fact that subclinical gastric lesions were found in racers with as little as a single day of exercise prompted us to think that perhaps many athletic dogs, not just sled dogs, are also at risk of exercise-induced gastric disease," Davis explains. A one-year grant from the Morris Animal Foundation is helping Davis and his team to evaluate field trial retrievers before and after a competitive event. If stomach ulcers are found in these retrievers, further research will seek to identify methods trainers and veterinarians could use to reduce risk through modifying training