Managed 10 minutes today mostly downhill and flat. No wheezing just sore throat

As soon as sat on the seat was in agony. Not just a bit but real bad. Had to peddle standing up. Are the gel seat covers on ebay any good?

Legs felt like jelly no power in them. Ob2 really unfit. Do I need to get fit some other way before starting cycling? I can't imagine 10 minutes a day going to do much good? I'm totally embarrassed how unfit I am