I am turning fifty next month and I have let myself go until I am so fat now (247 lbs.) I need desperately to get in hsape. I have an old single speed bike with a coaster brake, and I got it out today and aired it up. I loved bike riding as a young girl and starting out I loved the feeling of the wind in my face. However, after a ten min ride I was panting, sweating, heart pounding like a sledge hammer and my thighs felt like they were on fire. My doctor says there is no reason I can't exercise as long as I start out slow What is slow in cycling? Can a fat lady ride?