# Respiratory Muscle Strength as a Predictor of VO2 max and Aerobic Endurance in Competitive Athletes
## 4 Discussion
\begin{table}
\begin{tabular}{l c c c c} \hline \hline
**Variable** & **Coefficient (\(\beta\))** & **Std. Error** & **t** & \(p\) \\ \hline F-statistic & 22.60 & & & \\ Model \(p\)-value & \(4.61\times 10^{-1}\) & & & \\ \hline \hline \end{tabular} Notes: MIP refers to Maximum Inspiratory Pressure, while MEP stands for Maximum Expiratory Pressure. VE represents Ventilatory Efficiency, measured in liters per minute (L/min). VO2 indicates Oxygen Consumption in milliliters per minute (mL/min), and VCO2 is Carbon Dioxide Production in milliliters per minute (mL/min). VO2/Kg refers to Oxygen Consumption per Kilogram of body weight (mL/kg/min). The \(\beta\) values represent the regression coefficients, Std. The error refers to the standard error of the estimate, the t-value is the t-statistic used to test each coefficient, and the \(p\)-value indicates the statistical significance of each term.  
\end{table} 
Table 6: _Cont._group [34]. In contrast, [PERSON] and [PERSON] (2002) reported in a study conducted on 12 male competitive triathletes and marathon runners (N = 8 research, N = 4 control group) that breathing exercises (MIP 15%, performed twice a day for a maximum of 30 breaths for 4 weeks) did not cause an improvement in VO2 max capacity [35]. In another study conducted on young football players, it was reported that there was no significant change in VO2 max values after a four-week respiratory muscle training program [36]. Likewise, [PERSON] et al. (2002) conducted a study on 16 trained male cyclists (age = 29 \(\pm\) 3.3 research group, age = 30 \(\pm\) 2.6 control group), and they showed that inspiratory muscle training (6 weeks) caused no significant change in the VO2 max values of the subjects after respiratory muscle training. However, there is evidence that maximal increasing exercise attenuates the perceptual response to exercise, and there is evidence of improved performance in competitive cyclists after inspiratory muscle training [9]. During high-intensity endurance exercise, there is increased production of metabolic CO2. This excess CO2 needs to be removed by increasing ventilation. If the respiratory muscles are not strong or enduring enough to meet the increased demand for ventilation, the levels of CO2 in the tissues and blood will rise, leading to metabolic acidosis. This can cause both skeletal and respiratory muscles to fail. Therefore, expiratory muscle strength is important in this context [36]. We found a moderate positive correlation between MEP and VCO2 in our study, demonstrating the significance of expiratory muscle strength. Our study also revealed that subcostal circumference measurements in MEP during inspiration significantly affected VE. In line with these findings, it is predicted that increased development of respiratory muscles will result in higher air intake into the lungs per minute, leading to improved sports performance [37]. Efficient utilization of the respiratory muscles plays a critical role in sustaining prolonged aerobic activities. Enhanced respiratory muscle efficiency is commonly associated with improved exercise performance and overall endurance capacity [38]. Numerous studies within the literature have explored the efficacy of respiratory muscle training (RMT) as a means to augment exercise performance and optimize athletic outcomes, indicating its potential value in both elite and recreational athletes. For instance, [PERSON] et al. (2012) conducted a comprehensive systematic review and meta-analysis, demonstrating the significant benefits of RMT in improving exercise performance among healthy individuals [39]. Building upon this foundation, [PERSON] et al. (2024) explored the practical applications of RMT specifically within the context of endurance sports, shedding light on its potential implications for athletes [40]. Additionally, [PERSON] et al. (2013) conducted meta-analyses, providing compelling evidence for the efficacy of RMT in enhancing athletic performance across various disciplines [41].