ACE Personal Trainer Practice Exam

Co-contraction occurs when which of the following muscle types contract together?

1. Agonist and antagonist

2. Skeletal and smooth

3. Cardiac and smooth

4. Skeletal and cardiac

The correct answer is: Agonist and antagonist

Co-contraction refers to the simultaneous contraction of both agonist and antagonist muscles around a joint. This type of muscle action can provide stability and support during movement, especially when maintaining a posture or performing controlled motions. For example, when lifting a weight overhead, the biceps (agonist) are working to lift the weight, while the triceps (antagonist) may also contract to stabilize the elbow joint and prevent hyperextension. This interplay allows for smoother and more controlled movements, which is essential in various physical activities and rehabilitation settings. In contrast, other muscle type combinations, such as skeletal with smooth or cardiac, do not share the same functional relationship in terms of joint movement and stabilization. Skeletal muscle is primarily involved in voluntary movements, while smooth muscle controls involuntary functions in organs, and cardiac muscle pertains to the function of the heart. These different muscle types do not typically co-contract in the same functional sense as agonists and antagonists do during controlled movement.