Which exercise increases hamstring strength in Reformer 3?

The choice of Long Box Rocking as the correct answer is based on its specific targeting of the hamstring muscles. This exercise requires engagement from the hamstrings as the participant activates them to control the body's movement while rolling on the reformer. The mechanism of the exercise involves both stretching and contracting the hamstrings, which effectively promotes strength development in this muscle group.

Long Box Rocking also incorporates the use of the reformer's spring resistance, creating a challenging environment that further enhances strength gains. This makes it an excellent choice for focusing on improving hamstring strength.

In contrast, the other exercises listed do not primarily emphasize hamstring activation to the same degree. For instance, Footwork (legs in straps) typically engages more of the quadriceps and glutes, while Control Back Facing Ceiling focuses on upper body and core stability. Kneeling abdominals, on the other hand, are designed to enhance core strength, with minimal direct involvement of the hamstrings. This distinction highlights why Long Box Rocking stands out as the most effective choice for increasing hamstring strength in this context.