Whatever discipline you compete in or even if your dog is a working dog, the warm up is one of the most important factors in keeping your dog sound for the long term and injury free. I would advise warming up even when training, whether you are practicing speed and obstacle skills or improving general behaviour training, the warm up will help your dog stay focussed and limber. Warm up and cool down before and after every training session and competition, even if you are just training in your garden.
More than one study has looked at the effects of the warm up on injury rates, regardless of the sport and has found that dogs need to be warmed up for at least 9 minutes, otherwise muscle injuries are commonplace.
Start by brisk walking for 2 minutes, then trotting your dog for a few minutes (about 3 minutes) then introduce some cantering for a minute or 2, finally introduce some low jumps (for flyball and agility).
Include some active stretches after this, instead of holding your dog in a stretch, active stretching has proven, in both human and animal sport, to increase power and acceleration, while passive stretching, where the handler holds the dogs legs in a stretch, immediately before training and competing actually decreases performance. Using a baited stretch, where a piece of food is used to move the dogs head around to his flank, while his feet stay where they are! Move the dogs head between his front legs, by getting his nose to follow a treat, repeat on the other side. Active stretching prevents the muscles from being overstretched before strenuous exercise. Ask your dog to stand with his front legs on top of a box, to stretch the back and hind leg muscles. Teaching or encouraging your dog to “play bow” on command helps to stretch the shoulder, triceps and back muscles.
Finally at the end of the session remember to cool down effectively, 10 to 25 minutes of walking, start at a fast walk, then gradually change to a slower pace.