Electromyogram (EMG) activity in the lower extremities during quiet standing is fairly continuous in which of the following muscle groups?

The answer, involving the soleus and gastrocnemius muscles, is correct because these muscles play crucial roles in maintaining posture and balance during quiet standing. The soleus, in particular, is highly active in responding to gravitational challenges, providing constant support to keep the body upright. The gastrocnemius also contributes to this stability but is more involved in activities that require dynamic movement.

During quiet standing, the continuous electromyogram (EMG) activity of these muscles indicates that they are consistently engaged to manage changes in balance and to maintain an upright position. This sustained muscular activity is essential for preventing postural sway and ensuring stability, particularly when the body is static.

In contrast, other muscle groups listed might not show the same level of continuous EMG activity during quiet standing due to their different primary functions—such as movement or dynamic support—rather than statically holding a position.