There was a documentary on over 20 years ago featuring the rivalry between Obree and Boardman. I remember one clip where G.O. was out on some undulating training rides and climbing in an absolutely massive gear. I think that he said that he did it to make his legs stronger. I wouldn't recommend that to most people, but it clearly worked for him! (Well, I suppose he might have been even better if he had trained a different way, but we will never know that because he didn't.)
Ooh - I just found it on YouTube and am watching it now on my Smart TV ...
Note the rust on Obree's little exercise bike caused by his sweat!