Most important bodyparts in trials

When I was at the worlds in Canberra, watching the 26" elite I heard 2 guys talking.
1: "hey look how high they can jump, they must have really powerful legs!"
2: "it seems like they use their lower back more"
and that is absolutely true, watch any trials video and you can see that the lower back gets a lot more range of movement than legs.
Ill use a picture of Damon Watson here to explain it a little better

You can clearly see how much movement the lower back gets.
The best exercises to get your lower back more powerful are squats and even better are deadlifts. Most trials riders can deadlift quite a lot even when they have never been in the gym, because riding has made it a lot stronger.

Next is legs and upper back. Legs arent used as much as lower back but they are still very important, like in vertical jump.
About the upper back, lats are very important because they help you to pull the handlebar towards you. If your lower back and legs are super strong but your lats cant keep up with them you wont be jumping very high. A chain is only as strong as its weakest link. To improve them the best exercises are pullups and barbell rows, and hold the bar about as wide as you hold your bikes handlebar.

So the most important bodyparts in trials are:
1. lower back
2. upper back and legs (TRA says that front squats are even better to improve legs because then you will get more work for quads)
3. forearms, bicep, tricep (for forearms you dont need to do extra work when you are already deadlifting and doing weighted pullups but you can if you want to)
4. everything else