So, I was in colorguard in high school. One year, our routine required us to drop suddenly into a kneeling position. I don't know what the rest of the guard did, but I dropped hard onto my knees every time, and spent the whole season with dramatic bruises on my knees. When I went to the doctor's office that year, she inquired about my bruises, then explained that she's always happy to see a few scraps or bruises on little kids' knees, since it means they're running around outside, instead of just watching TV. (The she suggested that I might want to try knees pads.)
And my Andover doctor (who I loved, and who knew how much I run and bike outside), once told me after examining my pasty skin for unusual moles or freckles that it was OK to go outside from time to time without wearing SPF 873 sunscreen--I didn't want to be so obsessed with avoiding sun damage that I gave myself a vitamin D deficiency.
The good news is that they'd both be proud of me after this weekend... I have an interesting assortment of scraps and bruises on my legs (admittedly, some are from wearing slippery shoes to work and falling over spontaneously, but the rest are from learning how to use clipless pedals on my bike and falling over spontaneously), and some decidedly pink areas on my shoulders and back, from biking 50-some miles. (For actual information about the ride, and a picture of clipless pedals--which seem to me to have clips--visit Kevin's blog.)