Which of the following Reformer exercises should be approached with caution for clients with lower back problems?

The Hundred is a Reformer exercise that involves coordinating breathing with a rhythmic pumping of the arms while holding the upper body off the mat and engaging the core. This exercise emphasizes core stabilization and requires a degree of spinal flexion. For clients with lower back problems, The Hundred can present challenges due to the position of the spine and the potential strain on the lower back. The strain may be exacerbated if the client lacks sufficient core strength or flexibility, which is often the case for those dealing with back issues.

In contrast, other exercises like Teaser, Plank, and Bridge can also be beneficial or neutral depending on the technique and modifications applied, but The Hundred requires a specific balance of strength and control that may not be suitable for all clients with lower back problems. Therefore, caution is warranted with The Hundred due to its demands and the risk of exacerbating existing back issues.