Looks like the ones used in the study are an order of magnitude more expensive than the ones on amazon. Amazon (Plus model), $70: https://www.amazon.com/POWERb

Looks like the ones used in the study are an order of magnitude more expensive than the ones on amazon. Amazon (Plus model), $70: https://www.amazon.com/POWERbreathe-Fitness-Breathing-Trainer-LSI-Plus2/dp/B000NJMLPA/ref=sr_1_5?crid=2XUZPPY0CGIBV&keywords=POWERbreathe+K3&qid=1649983213&sprefix=powerbreathe+k3%2Caps%2C113&sr=8-5 https://www.amazon.com/POWERbreathe-Fitness-Breathing-Traine... From manufacturer (K3 model), $500: https://www.powerbreathe.com/product/k3/ https://www.powerbreathe.com/product/k3/