Can I just add that in the 8 weeks running up to my LEJOG I worked in an laboratory (not the kind that needs white coats) and had to shift 2500kg of animal feed in 20kg bags from pallets to the animals' troughs. Now that combination of stop/start, lift, carry, and carefully put down was tremendous for developing much better muscle strength all over my body - and in all sorts of flexible ways which certainly made the cycling a lot more comfortable, so I'd argue that weight training helps cycling. You don't need a gym membership to try this - just a couple of filled hessian sacks and some space.