I bought this abdominal breathing trainer and the effect is amazing! It is simply designed, easy to operate and has no difficulty getting started at all. Inhale under the guidance of the trainer, and your abdomen will naturally bulge. Exhale evenly and smoothly. Each time you use it, you can clearly feel the increase in breathing depth. After persisting for a period of time, breathing becomes smoother, sleep quality improves, and stress is also reduced