This is very true. Long ago I started biking to work, and biking really hard - basically making the best time I could. The first few weeks, at the end of a 10

This is very true. Long ago I started biking to work, and biking really hard - basically making the best time I could. The first few weeks, at the end of a 10 minute sprint, my heart would be racing and I would be out of breath for 5 minutes after arrival. I was amazed after 2 months of doing the same thing I wasn't out of breath, it took maybe 1 minute for my heart rate to slow back down.