Review on Maximize Your Stamina and Performance with POWERBREATHER Sport by Damon Mertz

I swim four days a week and use a snorkel because I have problems with my neck. I have used Powerbreather 4 times and found it difficult to inhale during my workouts. A few days later my chest hurt and I thought I might have pneumonia or some other lung problem. I visited my doctor and he said my lungs were clear and I might have muscle tightness due to difficulty breathing with the Powerbreather. Haven't used it since but plan to try again soon. I think it might be useful once you get used to it. For $100 I feel like I should get more out of it.