Panting has nothing to do with a dogs wind or stamina. Panting is a dogs version of sweating as they have no sweat glands in their bodies except for in their feet, and almost all cooling is done via the mouth through the bloodstream internally. The way a dog cools his body is by panting. On a hot day a dog with great stamina will pant just from the heat. Men sweat more than women, I read that this is because men have more muscle mass and typically require more sweating which is the body's way of cooling itself. The better a body cools itself the better it can perform in high stress, high energy, and high heat activities. It only goes to reason the more readily a dog pants the more efficiently it can cool itself. The panting has no relation to a dogs stamina, the sooner he pants the sooner he begins cooling his body, the longer he pants after an activity has a lot to do with the temperature and the time it takes his body to cool down. As his panting slows his body temperature is returning to normal levels. The minute a dog begins to exert himself his breathing and panting increase to counteract the heat generated as his body and muscles warm. The bottom line is panting is really not related to a dogs ability to perform physically other that how it relates to dissipating heat. Your dog is not breathing hard as does a human when his cardio vascular and pulmonary system is being stressed. He is cooling himself. A marathon runner will sweat profusely while barely breathing hard, where a dog will breath hard or pant just from temperature with no exertion what so ever. Judging your dogs conditioning by how he pants is not a good idea. If you're riding a bike don't judge by the panting judge by the distance he goes without slowing or stopping.