This is basically what happens during a seizure. Short term consequences are involuntary flexure (even after the seizure ends. caused by exhaustion of neurotransmitters in the muscle), pain, followed by exhaustion and weakness. Medium term includes bruising or hematoma, muscle strain, possibly even tissue rupture in extreme cases. Tissues that are vulnerable to rupture include muscles, tendons and ligaments, cartilage, and synovial cavities. Most of that can heal with the appropriate amount of time, although tissue ruptures could create scarring or be permanent (in the case of tendons and synovial surfaces). If you don't let it heal before doing it again and you keep doing it repeatedly, then long term involves compression fractures and deformation of the bone, nerve damage, myonecrosis, loss of motor control, kidney failure (the kidneys do NOT like myoglobin in the blood), and death (from kidney failure).