What is a precaution to consider when performing the "criss-cross" exercise?

The precaution of avoiding lateral flexion of the trunk during the "criss-cross" exercise is essential for maintaining proper form and protecting the spine. The criss-cross exercise emphasizes the rotation of the torso while engaging the oblique muscles. If lateral flexion occurs, it can place unnecessary strain on the lower back and disrupt the exercise's intention of developing core stability and rotational strength. Ensuring that the body moves in a controlled manner helps focus on the targeted muscle groups and prevents injury.

While the other options may address important aspects of performing exercises safely—such as maintaining a straight back or keeping the head stationary—these are not the primary concern in this specific exercise. Furthermore, using weights for resistive training is generally not a standard practice in criss-cross, as the exercise typically relies on body weight and core engagement rather than additional external weight. Thus, avoiding lateral flexion is the key precaution to ensure effective engagement and minimize the risk of injury.