Enhance Endurance: This portable breathing trainer is great for boosting endurance during high intensity workouts through deep abdominal inhalation exercisesAdjustable Resistance Levels: Equipped with an adjustable resistance knot, this device allows users to customize the level of resistance to match their fitness level and training goals, making it versatile for a wide range of usersImprove Athletic Performance: Suitable for individuals at all fitness levelsfrom athletes and singers to seniorsMaterial: Made from flexible silicone, our breathing trainer offers comprehensive respiratory muscle training for various usersSize: Its compact design ensures comfort and convenience during use, measuring just 10*5cm for easy portability Specification: Material: Silicone Size Chart: 10cmx5cm/3.94inchx1.97inch Package Includes: 2 Breathing Trainer Note: Please allow slightly errors 1-2cm/0.39-0.79inch differences due to manual measurement.