THere is an article on exercising your dog in this month's Dog Fancy (my old collie is having serious old age health issues - I spend way too much time in vet waiting rooms). It talks about building up your dog's distance/endurance slowly - and not over doing it - as well as signs to look for when to give dog a break/rest. Another thing to keep in mind is feeding times to run time - some dogs are susceptable to bloat etc if they eat and exercise too close together.