yes, they do (although I would not consider myself to be athletic I did ride a push bike for a great part of my youth, and was able to cover some long distances and reach some impressive speeds). This is provided they are combined with adequate rest and food inbetween training; although they won’t turn someone into a superhuman overnight and if the sport involves taking quick decisions as well as physical endurance on a repeated and known task the enhancement is not as great. it might not be as good for team sports as individual sports).
There is also the significant risk of stroke/heart attacks if you overdo things, which is why the stuff ended up on the banned list and became a controlled substance in the first place. I never got into competitive riding but one of the local speed dealers I knew then always rode a particularly well equipped bicycle (100% legit as in no part of it stolen); often with components that were very new and there was only 1 or 2 sets of them in the whole country.
He also supplied a lot of higher level amateur riders; who would pay him at least in part in bicycle components (many British cops still ride bicycles on duty and as a pastime, and are members of the same clubs. So these riders did not want to look overtly like drug users, by doing this any cops would have just thought it was two blokes talking about bikes and trading components)
