I have one friend who runs every day (and runs pretty fast). His grand total of official races he’s run? One. He just does not do races. Another friend, who also runs every day, once logged around 40 races in one year. And somewhere between those two is another friend who runs perhaps three times a week but plans to run 17 races this year.
What’s the proper amount of races per year in which to participate in comparison to just training? Having races for which to train can help motivate people to keep running even in the dead of winter, the sogginess of spring or the heat of summer. On the other hand, too many races can burn someone out. In fact, having too many races may actually be detrimental to your performance due to lessened training and recovery time.
Personally, I run five or six days a week and “limit” myself to no more than a dozen races a year. Ideally, the races are spaced out so I can do specific training for each race (more speed work for 5Ks and 4 milers as opposed to more long runs and tempo work for half and full marathons). Because of race week diets (such as added salts, carb loading and decreased alcohol intake) and race day exertions, I personally feel that each race experience is draining and takes a lot out of you. Additionally, I try to ensure that I am adequately prepared for each race so that I am possibly in line to set a personal best each time. Many good runners can roll out of bed and run a 5K hard or complete a half marathon, but unless they have done some race-specific training, they probably would not be able to do as well as they possibly could in a race of that distance.
One exception to limiting yourself to races for which you can fully train is if you are using the race itself for part of the training for another race. For instance, if the big fall race you are targeting is a marathon in October, you may want to sign up for a half marathon that takes place a few weeks before the marathon. While you may not have the speed or pace for the half had you been specifically aiming only for that race, you can still test your fitness at perhaps marathon pace at that distance.
So I believe the answer is to limit yourself to a manageable number of races so that you can properly train for each race, with the exception of using a particular race to help train for a more important race.