There's no official distance for a sprint in pigeon racing. A marathon is about 600 miles, although many long-distance races fall between 500 and that number. A sprint is only a fraction of that, and to improve your chances of winning you should put your pigeons on a sprinting diet, check your birds for strong muscles and feather health, and use only your strongest birds in the race.
A diet rich in proteins and grains, and slim on fat, is a good diet for short-distance pigeons. Feeding the birds a diet of barley, rice, wheat, and some seeds gives them mainly proteins, fibres, and sugars to power their body. The more you change out grains for seeds, the more fat and oil the birds will take. This may be good for long-distance flying, where the energy stores of fats really counts, but for racing sprints you'll want to stick to a lighter mix of grains.
Checking Your Birds
Dr. John Lamberton, a birding enthusiast and pigeon racer, says that evaluating a pigeon's health and vigour is one of the most important tasks in getting good results in a race. If you put unhealthy or comparatively weak birds in the air, you're not going to do well. Fortunately, evaluating the health, vigour, and strength of your birds isn't that difficult. When holding the pigeon, one hand pressing the legs to the body and the head facing your stomach, you can press your palm against the pigeon's feathers. There should be some resistance. If there's not, the pigeon is not that strong. You can also feel for the density of feathers by running your hand down the ventral side of the body. This area should be replete with many feathers.
Your Best Birds
You'll want to use your best birds in a sprint. Having many training sessions before the official race, as well as checking the evening before the race will help you find which birds are healthiest. The strongest birds have long, thin flight feathers, a flat breast, proportionately sized head and wings, feel buoyant in your hands, and have a keel bone about the length of one of your fingers. It'll take practice getting used to feeling for the differences among your birds using your hands, but as long as you have trial sprints you can see which of your birds did best, and get a feel for them in your hands so you know what to look for.