The hardest ride I ever did was my first road bike ride in 15 years, right after moving to the SF Bay Area in the mid 90s. I borrowed a friend's bike and went with him and a group of his friends up Mt Hamilton. It's not a particularly difficult ride, except I was completely unprepared for it. I thought I was going to die. Several times. But they all did it with ease, riding very slowly (kindly, on my behalf) and chatting while I was doing my best to stay upright and turn one pedal at a time. I made it though; I felt like this would be a ton of fun and very enjoyable if I could do it as easily as them - so by next week I had bought a bike and was hitting the hills 2-3 times per week to get in cycling shape.
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"This 7:48 cycling session burned 5933 calories. Speed up recovery by replacing them with a healthy snack." - Whoop