What term describes the alternating contractions of opposing muscle groups?

The term that describes the alternating contractions of opposing muscle groups is known as a "tremor." Tremors are involuntary, rhythmic muscle contractions that can cause shaking movements in one or more parts of the body. They typically involve the opposing muscle groups contracting and relaxing in a coordinated manner, which leads to the characteristic oscillatory movement.

In contrast to tremors, cramps and spasms refer to involuntary muscle contractions but do not inherently involve alternating contractions of opposing muscle groups; rather, they often involve a single muscle or a group of muscles contracting simultaneously. Seizures involve abnormal electrical activity in the brain that can lead to a range of symptoms, including convulsions, but they are not specifically described as alternating contractions of opposing muscle groups. Understanding these distinctions helps clarify why "tremor" is the correct answer for this particular question.