Dear Bas Rutten,I wanted to tell you how impressed I am with your O₂ Trainer. Since purchasing it, I have used it with my Krav Maga training. I have also used it with the Bas Rutten MMA Workout. What a challenging workout when combined with the O₂ Trainer!! I have noticed remarkable gains in my stamina in just a short time with the O₂ Trainer. This device will definitely be an item that I will train with for years to come.Thanks for making such an excellent product!