The Powerbreathe is an inspiratory muscle trainer promoted as improving inspiratory muscle strength (and consequently exercise performance) in athletes and patients with respiratory disease. No published evidence supports its efficacy.2
An advantage to training was observed when outcome was assessed by maximal static inspiratory mouth pressure (mean advantage 14.5 cm H2O, 95% CI 2.2-26.9 cm H2O, P=0.025). However. no significant difference was observed between the groups in any other parameter.2
The continued sale and use of the Powerbreathe device is not justified by our data.2
However Another Article suggest-
There were found 14 respiratory training devices available on the market and reported by published studies. However, three were not described in detail, due to lack of information. Amongst the 11 evaluated devices, all of them showed positive aspects and limitations that should be considered. Although some devices appear to be more advantageous than others, it is not possible to choose the best one, based only upon their technical information and clinical utility.
To select the most appropriate one, it is also necessary to consider the specific health condition, the nature of the impairments, and the purpose of the training. Furthermore, the professionals should also consider the purpose of the device, including whether it is for use within research or clinical contexts. Future studies with good methodological quality should investigate the efficacy of the other devices, which were not described in detail in the present review.
maximal static inspiratory mouth pressure-
Measurement of the maximum static inspiratory pressure that a subject can generate at the mouth (PImax) here