My back hurts when I ski a lot of moguls and bumps, why does this happen?
It is hard to know the exact reason why your back hurts when you ski a lot of moguls or bumps, it is best to get a ski instructor or work with a physical therapist to let them assess your movement pattern and body.

One potential cause to back pain when you ski moguls or bumps is if you are using your back to take the majority impact and absorbing the bump instead of your knee and hip. As you are hitting a bump, you want to keep your back as straight as possible and let your hip and knee take the impact. The movement pattern is similar to squatting down, where you want to drop your bottom down towards your ankle. The reason you want your knee and hip to take the impact is because those joints have much bigger range of motion compared to your back so as you hit a bump or mogul, those joints will help absorb the majority of the irregularity in the terrain so your back is not needing to move as much which will help reduce the strain being put on it.