The curve of race participation

Next year, I move up an age group category for triathlon - to the 50-54 group - even though I won't be 50 until December of 2007. That's because of the "age up" rule - you race at the age you will be as of December 31 of that year. It's so that if you're trying to quality for Nationals (not in my wildest dreams) you stay in the same age group all season (rather than move up mid-season).

So, this year, when I've looked at race results, I've looked ahead to the 50-54 group results. And what it striking is the steep drop in race participation. For example, in this year's Subaru Triathlon, there were 36 competitors in the 45-49 age group and less than half that (17) in the 50-54 group. I was curious, so I plotted the age group distribution:

Age group participation

Clearly, there is a sharp peak at 35-39, declining rather rapidly after that.

The difference was even more striking in the running race I did on Sunday: 51 women in the 40-49 age group compared to only 10 in the 50-59 group.

Now, I expected some drop, but not this steep. I would love to know why. Most woman I know my age have more free time than when they were younger - kids are grown or close to it, they are established in their careers. There is well-documented evidence that for endurance sports individuals can continue to improve their performance, with proper training, well into their 50's.

I think it would make an interesting study: to understand why people appear to start dropping out of racing at age 40. It might say something about how we percieve aging.