Reference values for respiratory muscle strength measured with the S-Index Test in well-trained athletes, e-sports athletes and age-matched controls.

Respiratory function assessment is crucial in optimizing athletic performance, safeguarding respiratory health, and ensuring athletes can perform at their peak potential while minimizing the risk of respiratory-related issues. The S-Index Test is a dynamic evaluation of respiratory muscle strength. However, no comprehensive reference values regarding the S-Index Test have been reported yet. A total of 597 participants performed the S-Index Test. They were either well-trained athletes (WTA), or e-sports athletes (ESA), or age-matched controls (AMC) groups. The differences in S-Index Test results between sexes and for group-sex, and performance calibre tier-sex interactions were examined. The relationships between S-Index Test results and age, anthropometric indices and training experience were assessed. Reference values for all the groups were provided. Amongst athletes, the highest values were observed in swimmers and rowers, and the lowest in figure skaters and runners. The S-Index Test results were different for the group-sex interaction (P = 0.004, 151.6 ± 29.0 cmH 2 O for WTA males and 109.8 ± 21.6 cmH 2 O for WTA females, 136.7 ± 28.0 cmH 2 O for ESA males and 101.8 ± 22.0 cmH 2 O for ESA females, 128.7 ± 28.8 cmH 2 O for AMC males and 70.3 ± 24.7 cmH 2 O for AMC females) and higher in males than females (P < 0.001, 145.1 ± 30.5 cmH 2 O for males and 100.8 ± 27.6 cmH 2 O for females). The higher athletic level, presented as performance calibre tier, was not linked to higher respiratory muscle strength in the WTA group (P = 0.094). However, the Bonferroni correction revealed that except for the singular tier in females, there was a significant effect for all the other tiers and sexes (P < 0.001). The obtained results confirm that regardless of the level of physical activity, the anthropometric features are positively linked with respiratory muscle strength. Furthermore, age and training experience were positively correlated with the S-Index Test results in the WTA group.