Aim: To measure the effect of inspiratory muscle training, i.e. the strength and endurance of respiratory musculature and pulmonary function in children with regard to playing sports. Methods: The research is retrospective, data were collected over the period of 3 years, from 2014. to 2017. All subjects made 10 continuous arrivals in 2 weeks, with initial and final measurements on the Respifit device and also including pulmonary function measurements. Results: 128 participants were divided into 2 equal groups, of which 57% were male and 43% female. Respondents were 10 to 17 years old. A statistically significant difference of less than 0.005 was observed in both groups when testing maximal respiratory muscle strength (Pimax cmH20), p <0.001. The median for the initial Pimax (cmH₂O) is 96,000 with a range of 76,000 - 116,500, while the median for the final Pimax (cmH₂O) is 130,000 with a range of 113,000 - 144,500 in the first group (athletes). The median for the initial Pimax (cmH₂O) is 90,500 with a range of 71,000 - 107,500, while the median for the final Pimax (cmH₂O) is 121,000 with a range of 97,500 - 142,500 in the second group (non-athletes). A statistically significant difference between the two groups is in the difference in peak expiratory flow (L/s), p = 0.043. There is no statistically significant difference between the sexes or between individual or group sports in this study. Conclusion: The group of children involved in sports has a statistically significant peak expiratory flow relative to the other group, but both groups have an increase in values on the IMT device versus the initial measurement. Due to the lack of publications performed on IMT devices in children with asthma, further research and an increase in the number of subjects are needed.