I am a climber (currently doing mostly bouldering - short, powerful and very dynamic climbs) and I recently have issues with sore back muscles - I can barely move the next day after exercises and the following few days. What can I do about it other than making sure I warm up properly and stretch? Should I try any vitamins or other supplements?
There are a couple sources of pain, particularly for the lower back. These are:
DOMS is characterized by a dull soreness that can range from a general feeling of being "used" to a more intense feeling of soreness inside the muscle. Usually, after the same type of stress repeated regularly (such as every other day), the body gets used to the stress and returns to a state of normal rather quickly. Eventually the pain can even disappear.
Injuries on the other hand can range from very small tears (a normal part of getting stronger) which can cause pain for a couple days. The more severe the injury the more severe the pain. Injuries can be caused by a lack of flexibility, a lack of core strength (in the case of the back), and poor technique.
Ironically, the long term solution is essentially the same in both cases. The only difference is that you have to let an injury heal first.
After your bouldering exercises, I recommend a cool-down period. In this cool-down you'll do the stretching you need to improve your range of motion, but don't over-stretch (meaning don't push past the pain). The very next day when you can barely move, try to get your blood flowing with a simple warmup. You'll probably have to go slowly, but it is worth it. Then foam roll and do more stretching.
In essence you can stretch daily, and the more you limber up, and foam roll the soft tissues, the better you will feel and the quicker you will recover. If your bouldering activities are all on the weekend, you should have a couple days for building core strength in between during the week. Even if you don't have access to barbells, kettle bells, or anything like that, good body weight exercises will help you improve your core strength.