I have figured this out for myself so I thought I would share it. The symptoms I mention in the title hit me a few times but I figured it out.
First it goes away after a few hours. But to avoid getting it, you should exercise hard only every second day. I was doing it every day and it was not good. It is sort of like using up all your energy. In between the hard workouts maybe do nothing or do a very short walk.
For me the hard workout was 4.5 KM walk over a variety of terrain.
I did not have pain in the beginning with ALS but pain started quick and it was constriction pain. It was easy to deal with - stretch the hand or if it was in my stomach lean back as much as I could. But by keeping legs straight when sleeping or watching TV helped and so did 250 mg of Magnesium. But then another pain started. I call it point pain as it happened in a specific point. It only lasted until I straightened out my leg or arm. So that is very good to know.
Once I had point pain that straightening my leg did help. It was the most pain I had felt in a long time. I straightened my leg but it took maybe 3 minutes to go away.
Another time I had back pain. I could not deal with it and it meant I had walk or sit very carefully. I tried taking Tylenol Extra Strength but it did not help. I was worried about how was I going to sleep. I added three glasses of red wine and between it nd the Tylenol no more pain.
Sometimes when you have a bad pain, it is a sore area after the pain goes. A hot shower helps with that.
I hope that this helps.