Ride a bike for 30 minutes.

“Went on my first ride yesterday after buying my first bike (since I was a kid). [...] Cycling is WAY harder than I thought. I rode for 20 minutes and got 5 miles with a total climb of 200ft. The hills KILLED me. Hills suck as a runner, but cycling? JESUS! When I got off the bike, I nearly fell from the soreness in my legs. I run for 30 minutes to an hour and range from 3 miles to 8 miles every day. I cycled for 20 minutes and I felt way more tired than a threshold hour long run. I have a LOT of work to do.”

“I thought of myself as a fairly fit 35 year old until I went on my first bicycle ride today. I live in a very hilly area and I got to the first fill and felt like my heart was coming out of my chest and my lungs were ablaze. I walked it up and felt so embarrassed. It took me about 15 minutes to catch my breath. I got back on my bike and got to the next hill and again felt like I was going to pass away. I turned back around and went back home whimpering with my tail between my legs. [...] This experience really really humbled me.”