When I was a ‘juvenile’ and started out riding the road, I used to go and see this coach called Harol Nelson (he had coached Paul Sherwin among others and was a BCF coach).
He was famous for using ‘rollers’ exclusively to train people. He had this set of ‘machined from solid billet stainless steel’ rollers that weighed a ton. You rode them with a fixed wheel track bike and big old tyres. It was like pushing a 100+ inch gear. I will never forget the first time I did the standard 30 minutes on those things.
But I never got beyond someone having to be there to prop me up/catch me. Getting started was the hardest part and then stopping was also pretty tricky.