Contraction muscle is a term used to describe muscles that are able to contract and relax. The three crossword solutions for this term are EER (3 letters), SPASM (5 letters), and EEN (3 letters). EER stands for electrical excitability of the muscle, which is the ability of the muscle to respond to electrical stimulation. SPASM is an acronym for sudden, involuntary muscle contraction, which is a common symptom of muscle fatigue. Lastly, EEN stands for electromyography, which is a technique used to measure the electrical activity of muscles.