You may be thinking that you are as fit as they come, but remember that dogs share a common ancestor with wolves who can run all day if they have to. This makes it difficult to over-exercise larger dog breeds, but smaller dogs and puppies have a definite limit on how far they’re able to go.
Knowing what's right for your particular dog is important when establishing an exercise regime
Get to know how far your dog likes to walk, and make each walk interesting by bringing a ball or a toy to retrieve. Training your dog while you’re out with him will also help to tire him out.
Some breeds of dog need a lot more exercise than others. For example, dogs like Labradors and Vizslas will do well with a long daily walk, but breeds such as the French Bulldog and the Pug risk serious health problems if they are over-exercised.
Exercising Adult Dogs
See how long it takes for your dog to tire and then work around that. If you are walking your dog off the lead and allowing him to run around then he will tire a lot faster, but if you are walking him on the lead then you may need to exercise him for longer. Dogs enjoy being taken for a walk, so make it fun by bringing a ball or toy to play with along the way.
An agility course is no problem for a fit dog
If you have an older dog suffers with heart or joint problems, avoid long treks, but let him wander around the garden or park under your supervision instead. Avoid taking an older dog out during the hottest part of the day because their ability to regulate their body temperature deteriorates as they get older.
Over-exercising a growing puppy can result in joint problems, particularly with Giant breeds like the Scottish Deerhound or Great Dane. As a general rule of thumb, a puppy should receive five minutes of exercise for every month of its age. For example, 10 minutes per day for a dog of 2 months, and 15 minutes a day for a dog of 3 months. This can be done in one or two walks per day, but until your puppy is at least a year old, it should be taken for no more than two walks per day.