Which exercise involves lying on your back and cycling your legs?

The exercise that involves lying on your back and cycling your legs is known as the supine bicycle. This movement engages core muscles as it requires coordination and stabilization while simulating a cycling motion with the legs. When performing the supine bicycle, the back remains flat against the ground, which is crucial for effective core engagement and to minimize strain on the lower back. Additionally, this exercise improves coordination, flexibility in the hips, and strengthens the abdominal muscles, making it a well-rounded addition to a fitness routine.

In contrast, the other exercises listed do not involve this specific body position or action. V-ups require raising both the upper body and legs simultaneously while seated on the ground. Prone rows are performed face down with weights, engaging the back muscles rather than the core. Swimmer involves a prone position as well but focuses on alternating arm and leg movements to simulate swimming. Hence, the supine bicycle is distinctly characterized by its specific lying position and cycling leg motion.