I didn't say flat back. I said straighten the spine. And working with a straight spine is good practice for just about any activity--lifting, skiing, sitting, standing, swimming, . . .

But if you must know, I first heard of riding with a flat back from Bill Farrell, the coach who conceived of the Fit Kit almost 40 years ago. Most beginning cyclists reach for the handlebar by bending at the waist and shoulders, and it really doesn't matter what kind of bike they're riding. The tendency to slouch is universal. But the more kinks you can get out of your spinal column, the better you're going to feel during the ride and after.

As a beginner I noticed that some days I couldn't get comfortable on my bike. The handlebar seemed too far away and I felt out of breath. Those were the days I hopped on and bent from my waist instead of the pelvis.