The PowerLung Trainer looks like an overbuilt plastic kazoo with a snorkel's mouthpiece at the business end. It is almost as easy to use as a kazoo. One of two numbered adjustable twist knobs varies the amount of resistance the device imposes against inspiration (breathing in). The other knob varies the amount of resistance your expiratory (exhaling) efforts meet.
In my first PowerLung session I just played around with these knobs and practiced breathing through the device until I felt I had found an appropriate starting level. Thereafter, in obedience to the literature that came with the PowerLung, I did two brief respiratory muscle-training sessions per day: the first during my morning commute and the second during my afternoon commute.
(Yes, I got more than a few strange looks from other drivers, but this was in San Diego, so most of the people who saw me driving with this overbuilt plastic kazoo sticking out of my mouth probably assumed I was just some surfer dude enjoying a newfangled water bong on his way to the beach.)
Within a matter of days I began to notice a training effect. It became easier and easier to complete the same number of repetitions with the same amount of resistance, so I incrementally increased first the number of repetitions and then the resistance.
It's now been about eight weeks since I started using the PowerLung, and while the strength and endurance of my respiratory muscles are markedly improved, I still can't say I've noticed an obvious improvement in my running performance resulting directly from these changes.
There have been moments, however, in hard workouts when I have felt less limited by my capacity to draw air—when my lungs have seemed to be coasting along even as my legs have begged for mercy. But it could be a placebo effect, for all I know.
When you've been an endurance athlete as long as I have, you have to start looking in out-of-the-way places for improvement. And it can be difficult to judge whether or to what degree a particular new out-of-the-way measure has contributed to any improvement you do experience.
Sometimes you have to take a leap of faith based on the results of controlled scientific studies showing that a particular tool or method really works. Such is the case with respiratory-muscle training. Several good studies have shown it enhances endurance performance when done properly.
So if you've been a triathlete for some time and are already training as hard as you're ever going to train, you might want to try respiratory muscle training.