I'm definitely NOT built to run (at least not fast)...short, stubby, heavy legs, BIG boobs (I was a 34DDD prior to reduction surgery), asthma...but I ran 1800+ SLOW miles last year.

Sure, some people are built to run fast, but we are ALL built to run. Humans are about the most efficient creatures on earth. Our ability to wear down our prey on-foot is what kept us fed for millions of years. We have big gluteal muscles to support running on 2 legs.

Biking is awesome...and I definitely seem to be more of a natural on the bike than I am on-foot, but running is great when weather conditions aren't ideal for biking (pouring rain, snow). Running is a more efficient workout than biking, too. I have a much tougher time getting my heart-rate up on the bike and I have to spend a lot more time cycling to get the same workout I can while running. The two pursuits really complement one-another.

Perhaps the best thing about running is the lack of necessary gear.