In simple terms, wearing this during training or a workout helps you regulate your breathing, increase lung stamina, lung capacity, oxygen efficiency and increase your overall performance not just in sport but daily life. The basic concept of this training mask is that it regulates how much air you can actually breathe in. This means that you are breathing against resistance which in turn makes the air feel thinner which is akin to training at altitude. From amateurs to professionals, this product has been approved to train with any sport that’s cardio based. Additional benefits of the training mask include: Strengthening the diaphragm and sculpts abdominals, conditioning the lungs by creating pulmonary resistance, increasing surface area and elasticity of the alveoli, increasing lung capacity and oxygen efficiency and increasing overall anaerobic thresholds. For optimum performance, please take into account the following sizes: * Large: 113kg – 136kg (250-300 lbs) * Medium: 68kg – 109kg (150-249 lbs) * Small: 45kg – 63kg (100-145 lbs) To help you get the most out of the training mask, a training booklet is also included and contains a series of exercises.