Ahh, hello tension my old friend…
Over the years I’ve picked up heaps of hand and forearm injuries, all related to tension. I’ve worked with hand therapists and osteopaths to settle things down, and it always comes down to minimising tension.
It’s two-fold for me - enough force to make the sound you need to, and time to release that tension, lest it build up.
The end point I keep coming back to is as little tension as possible. Fast, slow, moderate tempos are irrelevant. I need to play as light as possible, or the slightest tension will build over time and develop into injury. At the moment I’m dealing with a pain in my upper arm, tricep area, which has come from moving tension with speed higher up my arm, and also some incompatible shoulder rotating in some strumming passages.
If there’s pain always present, definitely address this first. See a doctor or someone who can get your body back into shape and give you some flexibility and strengthening exercises. Your playing has identified an imbalance, and it’s probably an easy fix, but is harder the longer you leave it.
My focus in practice and performing now is to be effortless and tension-free at all times. It starts with my pick grip, extends to my wrist mechanics, further in to my forearm, then upper arm, shoulder, back and neck. It’s all related. Over time my focus has extended through all of these, but I have a lot of work to do on shoulders still. Starting with being mindful of my hands helped a lot.
There was a LOT of relearning, I’ll be honest. But my technique is a lot better and I can play longer (8 shows a week at the moment) without pain. I stretch down after each show and try to warm up physically before I touch an instrument.
Sorry you’re experiencing pain. I get very jealous of guitarists who can play seemingly with whatever technique works for them and never experience injury. But I’m happy that my body has a very stern way of telling me I’m doing something wrong, quickly, because it’s leading me down a path of becoming more efficient.
The advice from others here is spot on about playing without tension, and avoiding speeds if your body isn’t keeping up. At higher speeds, any tension with be exacerbated.
I compare picking speeds to car or bike gears with students. At low speeds, you can use a little more force, as you’ll have time to recover between strokes. At higher speeds, you want to be floating through strings with zero tension. I can mostly identify 3 gears of speed and effort in my playing, you might have more. The important thing is they should feel different, and become lighter the faster you go, not become more tense.
The good news is your body should respond quickly. Get rid of the tension, let your arms and hands adapt, and you’ll find your technique will adapt to its new light regime in no time.