Spring tendons enhance the foot’s efficiency: some of the energy spent to drop one’s weight down when taking a step is actually stored and then returned to the leg as it rebounds.

So a few weeks after my birthday, in the spring of 2006, I walked into the office of a weight-loss doctor.

But, just like I didn't lose this much weight and body mass in a week or a month, my doctors expect it will take until late this spring to regain it.