Here is the proof

Bent’s phd research.

http://www.ncbi.nlm.nih.gov/pubmed/19960350

Nevertheless that was the question…

I would venture that time off the bike post season would provide a welcomed mental and physical respite. It is not possible to develop a balanced body if all one does is ride. Sooner or later those imbalances gained from chronic performance of one motion will cause the body to break down and performance to suffer.

Also, I don’t think the number of reps is the issue. More important than rep number is exercise selection, technique, and intensity. Thus competent coaching and supervision is crucial.

In theory it’s easy to argument that strength training is a great solution for cyclists in the off season. The major problem is that it’s not proven in scientific studies that you actually get better results than endurance training only.

One of the biggest problems for these scientific studies is that they are done at untrained people and the study group is usually small. That makes it rather difficult to prove a significant difference between endurance training only versus endurance training combined with weight lifting. My best guess is that strength training does make a difference and it is, at least in theory, possible to prove it with a larger study group. But the difference between including strength training or not, is obviously not the most important factor when it comes to overall performance in road races. Thus, it is very difficult to recommend you to either go to the gym or spend an extra hour on the bike. In both cases you will probably improve your overall performance level. It is important to notice that even though studies about strength training does not produce significant gains in overall cycling performance, it is very likely that there is a difference.

Your story with the rider who finished 4th illustrates the above. He would probably have done at least the same result if he had spend the same time training on his bike as he had spend time weight lifting.