The reverse plank forces your posterior chain to work against gravity in an unfamiliar orientation. Your glutes and hamstrings must generate tension working on long lever. Meanwhile, your scapular stabilizers, particularly the lower trapezius and serratus anterior, must maintain active shoulder positioning, while your shoulder joint reaches its end range of extension. Your abdominal muscles work isometrically to prevent arching, while your posterior deltoids and triceps create the pushing force