The Benefits of Stretchy Bands for Warm Up

I'm seeing more athletes actually using these super cheap $2, whatever, stretchy bands and cords within a warm up routine. And in general, you mostly see it to help increase the blood flow so that when you hop on the bike, you're ready to go. You're sitting straight on the saddle, you feel warm, you're loose, and you're able to engage all the stable little stabilizing muscles - not the prime movers in the cycling and pedal stroke.