# Respiratory Muscle Strength as a Predictor of VO2 max and Aerobic Endurance in Competitive Athletes
## 4 Discussion  
This study aimed to investigate the relationships between athletes' respiratory muscle strength, assessed via MIP and maximal expiratory pressure MEP, and aerobic endurance, as characterized by maximal oxygen consumption kinetics. It is noteworthy that approximately 16% of oxygen intake during exercise is utilized by the respiratory muscles. During maximal exercise (85% and above of maximum heart rate), approximately 14-16% of cardiac output is directed to the respiratory muscles [15]. Considering this aspect, the impact of respiratory muscles on performance is significant and cannot be ignored [26]. Our study found a negative correlation between VO2 max and measurements of the circumference at the mid-axilla and axilla during both inspiration and expiration, as well as at the mid-subcostal and subcostal regions during inspiration and expiration. In our study, we observed positive correlations between MEP and MVV, suggesting an augmented ventilatory response during exercise, where greater MEP and MVV capacity result in increased respiratory frequency. There are studies indicating an increase in maximum minute ventilation due to CO2 elevation during exercise [27, 28]. This, in turn, facilitates the swift elimination of carbon dioxide and enhanced oxygen uptake during physical exertion. Furthermore, [PERSON] et al. (2008) found that the respiratory muscle load during maximal exercise has a significant impact on tidal volume and CO in healthy trained individuals [29]. Another study conducted by [PERSON] et al. (2007) reported improvements in cycling performance following specific inspiratory muscle training, accompanied by an increase in anaerobic work capacity [30]. Additionally, [PERSON] et al. (2017) reported that improving inspiratory muscle strength through respiratory muscle training led to an enhancement in swimmers' maximum underwater swimming distance [31]. Lastly, differences in respiratory muscles between sports disciplines may result from variations in anaerobic or aerobic demands. The diverse nature of the group was crucial for enhancing the study's quality and diversity. In the literature, [PERSON] (2014) could not find a correlation between the MIP value and absolute or relative VO2 max values in male athletes but did find a correlation between the MIP value and absolute or relative VO2 max values in female athletes. In our study, no significant relationship could be found between relative VO2 max and MIP measurement results, which suggests that the athletes in our study reached their VO2 max value before reaching their maximum inspiratory muscle strength potential [32]. Previous studies in the literature have mainly focused on explaining the impact of respiratory muscle strengthening training on VO2 max. For instance, [PERSON] et al. (2011) found that a 4-week program of inspiratory muscle training enhanced the performance of the Yo-Yo test for two groups of 12 male football players competing in the national league. The training involved one set of 30 breaths twice daily at 50% of maximal inspiratory mouth pressure (PImax) and a pre-training inspiratory muscle warm-up of two sets of 30 breaths at 40% of PImax. This improvement was reported to be significant when compared to a control group [33]. In another study, [PERSON] et al. (2001) reported a study they conducted on 14 female competitive rowers at the commencement of rowing which found that the athletes' VO2 max value after respiratory muscle warm-up exercise performed with branch-specific general warm-up was higher than that of the experimental