What distance do you need to cycle before you feel you thighs/hamstrings/knees start to burn? So last week I was out most days, 20km cycle one day, the other around 10km, not far I know. By the end of the week I'm thinking I'm Lance Armstrong, legs feel strong etc. I am whizzing up any hills. Went out today and feel pretty rough, legs burning a bit after a km. Thinking to myself how can this be already. What's your story, I am sure you've probably been cycling for years and your legs are like machines but do you ever go out and feel like your starting from square one again?