"Effects of respiratory muscle training on performance in athletes: a systematic review with meta-analyses"
Hajghanbari B, Yamabayashi C, Buna T, Coelho J, Freedman K, Morton T, Palmer S, Toy M, Walsh C, Sheel AW, Reid WD.
More research recently published (July 25th 2012) to determine if respiratory muscle training (RMT) improves sport performance, and respiratory muscle strength and endurance.
The conclusion revealed that RMT can improve sport performance. Inspiratory muscle strength and endurance improved in most studies, which in part, was dependent on the type of RMT employed.
Read the Abstract online at The Journal of Strength and Conditioning Research