The LO2 Snorkel Top is compatible with the Adult and Junior Hydralign Center Snorkels for swim training. Breathing is an intricate part of swim training. A swim snorkel allows you to concentrate on a proper stoke and kick without having to turn your head to breathe. This helps our kick and stroke but does not improve respiratory efficiency. The Hydralign LO2 Training Snorkel Top is a respiratory training device to add to the top of the Hydralign Snorkel. This uniquely designed device with 3 levels of air flow restriction, improves inhalation muscle strength and simulates high altitude training by restricting oxygen intake. The Snorkel Top is made from corrosion and impact resistant plastic and is easy to install.