College of Massage Therapists of British Columbia (CMTBC) Practice Exam

Which contraction occurs when muscle force is exceeded by an external force?

1. Eccentric contraction

2. Isometric contraction

3. Concentric contraction

4. Static contraction

The correct answer is: Eccentric contraction

An eccentric contraction occurs when a muscle lengthens while under tension, which typically happens when the force generated by the muscle is less than an opposing external force. In this scenario, the muscle must allow some lengthening to occur as it tries to maintain a certain position against a load that is too heavy to lift. For example, when lowering a weight or descending stairs, the muscles controlling the movement engage eccentrically to manage that load safely. This is distinct from isometric contractions, where the muscle generates force without changing length, effectively stabilizing a joint or maintaining a position without movement. Concentric contractions involve the muscle shortening as it generates force sufficient to overcome an external load, which is not applicable in this scenario. Static contraction is a term often used interchangeably with isometric contractions, further affirming that these types of contractions do not illustrate a scenario where an external force exceeds muscle force. Thus, the concept of an eccentric contraction best captures the situation where the external force surpasses the muscle's ability to generate force, leading to a lengthening of the muscle under load.