MUSCULAR JERKS is a term used to describe involuntary muscle contractions, such as spasms and TICS. Spasms are sudden, involuntary contractions of a muscle or group of muscles, usually caused by fatigue or injury. TICS are sudden, repetitive, nonrhythmic movements or vocalizations that are often associated with nervousness or excitement. Both spasms and TICS can be uncomfortable and disruptive, and can interfere with daily activities.