Isn't there a device currently on the market that restricts your breathing for you...
It seemed quite clever the last time I had a look.
www.powerbreathe.com
This?
they've been around for years, one of the crews I used to row for got given a bunch for free... seemed pretty good but I never got into the habit of using regularly.
www.powerbreathe.com
This?
they've been around for years, one of the crews I used to row for got given a bunch for free... seemed pretty good but I never got into the habit of using regularly.