FWIW - I have been MTB racing for a few years, and have worked my way up to the Expert level. All this has been done without ever setting foot in a gym, or lifting any weights.

You need time on the bike. Find a training partner - someone just a bit faster than you, and train together. Go for longer rides - at least one 2-3 hour ride on the weekend.

I also race 'cross, which has some running, and never train for that part of it. However, for me, the running I have to do is short.

I have just this year started added a weight regimine to my training (this after 15 years of MTB, 4 of those racing, and 4 years of road racing), but it is primarily arms/upper body/core. I do very little in terms of strength training for my legs.

Just my $0.02.

SheFly