Listening to the podcast that Jonathan did with the “Go to Bed” Folks. What you describe sounds like compartment syndrome. Basically in the forearm and the lower leg, the muscles are separated from eachother by fascia. The fascia compartments are fixed to the bones in the limb. Anything that causes swelling in the compartment will cause the symptoms you describe. The pressure prevents nerves that pass through the compartment from passes impulses. In the case of motocross, the chronic vibration associated with intense contraction leads to muscle damage and swelling in the compartment. The surgery you describe is called a fasciotomy. There are times when this has to be done as an emergency. Its not from blood being “trapped” in the muscle.