Dogs, as well as humans, need regular exercise to keep them (us) healthy and looking fit. if your dogs have access to a large pen in cool weather and are turned out with at least one playmate, they will exercise themselves, by playing tag and other "collie" games. If you do not have these conditions, your dogs may become a bit lazy, and may need alittle encouragement. Do not, however, force any dog to perform beyond his/her ability. Do not force a dog (especially a rough-coat) to perform in hot weather. If the dog must perform in hot weather (agility or obedience competition outside), hose the dog down with water first.
Daily long walks, are great for dog and human alike, to keep muscle tone and aerobic fitness, with a minimal toil on the joints. An occasional sprint to raise the heart rate is also good for the spirit. Long slow trots seem to improve the hind-ends of some collies to combat 'cow hocks'.
An added benefit: Walking / trotting a dog on the usual urban or or suburban pavement will help keep the back (and sometimes front) toe nails nicely worn, with out having to clip them.
Walking is the most popular form of regular excersise claimed by American adults today, and those with dogs, get more than the average of this beneficial exercise