Introduction: Previous research has shown that inspiratory muscle training may improve endurance performance in competitive athletes in a range of sports. However, few studies have tried to investigate the effect of respiratory muscle training on swimmers. Due to the specific characteristics of the respiratory system in swimmer girls, this study examines the effect of inspiratory muscle training on swimming performance of swimmer girls.
Methods: Sixteen members of the females swim team of Kermanshah province voluntarily participated in this study and were randomly divided in two groups of sham training )with mean age 10/75 ± 1/98 yrs, Height  140/68 ± 14/7 cm, weight  32/17 ± 10/61 kg) and experimental group, each consisting of 8 participants )with mean age 10/75 ± 2/18 yrs, Height 143/68 ± 13/62 cm, weight 36/6 ± 9/01 kg) and were trained for 8 weeks (3 sessions per week, 30 breaths per session). Training intensity in the experimental group was equal to 5 (severe) and in sham training group was equal to 1 (very slight) in modified Borg scale. Before and after the exercise protocol 100m, 200m and 400m swim tests were performed. To analyze the data, independent and dependent samples t-test were computed by SPSS software at the level of significance (p<0/05).
Results: The findings of this study illustrate that after inspiratory muscles training, swimming performance of the participants in the experimental group in the 200 (p=0/007) and 400 (p=0/006) meters swim test improved significantly (p<0/05), but at 100m, mean changes were significant (p= 0/1).
Conclusions:  This study demonstrates that physiological adaptation in respiratory muscles that may occur after IMT
training can explain the significant improvement in 200 and 400 meters swim test in experimental group, but cannot account for insignificant results in100m swim. As yet, the causal mechanisms involved are undefined but they may be due to delay respiratory muscle fatigue.