# Respiratory Muscle Strength as a Predictor of VO2 max and Aerobic Endurance in Competitive Athletes
## 4 Discussion
Another study conducted by [PERSON] (2018) contributed to the body of knowledge by reviewing the ergogenic effects of RMT in healthy individuals, further substantiating its potential benefits in exercise settings [42]. Likewise, [PERSON] et al. (2015) investigated respiratory adaptations in athletes across different sports disciplines, highlighting the versatility and applicability of RMT strategies [43]. Lastly, [PERSON] (2020) conducted a study focusing on specific respiratory muscle adaptations in males engaged in both endurance and strength training, providing valuable insights into the physiological mechanisms underlying RMT benefits [44]. The studies mentioned above emphasize that RMT is an effective strategy for improving exercise performance and athletic outcomes in diverse populations and settings. Endurance training is thought to delay the onset of respiratory muscle fatigue and improve the efficiency of oxygen utilization. As respiratory muscle development progresses, it is expected to increase air intake volume, leading to a positive impact on sports performance [3]. Additionally, enhancing the strength of respiratory muscles not only enhances performance but also helps in preventing injuries. For instance, previous studies demonstrate significant improvements in respiratory muscle strength and functional outcomes, indicating potential benefits for injury prevention and recovery [45]. Increased respiratory muscle strength can assist athletes in maintaining proper breathing mechanics during intense exercise, reducing the risk of fatigue-related injuries and respiratory distress [46]. Furthermore, research has found inconsistencies in the effects of inspiratory muscle training on athletic performance. Some studies show significant benefits, while others do not demonstrate meaningful improvements. These discrepancies may be due to the use of standard inspiratory muscle training protocols without considering individual differences [47]. Additionally, RMT is associated with extra stress and training load. Therefore, such training methods should not be unconditionally recommended without considering the broader context [48]. Lastly, our study found a negative correlation between VO2 max and chest circumference measurements at rest, during inspiration, and expiration, as well as diaphragm circumference measurements at rest, during inspiration, and expiration. In contrast, positive correlations were observed between MEP and MVV values. In a resting state, the diaphragm or external intercostal muscles alone are sufficient for adequate respiration. However, during intense exercise, the effectiveness of the diaphragm decreases, and accessory muscles such as the scalene muscles, pectoralis minor, and sternocleidomastoid muscles gradually come into play to assist with inspiration [49]. During calm breathing, expiration is passive because the chest wall and lungs tend to return to their original state due to their elastic properties. During exercise, the internal intercostal muscles become active, responsible for forceful expiration. The contraction of these expiratory muscles, which reduces intrathoracic volume, increases lung compression [50]. Hence, this suggests that when exercising, the respiratory system is more active. This may be due to stronger expiratory muscles and a higher maximum voluntary ventilation, leading to a faster breathing rate. This helps in quicker removal of carbon dioxide and faster absorption of oxygen. It is well-documented that there are two distinct phases of respiratory increase when physical activity begins. Initially, there is a sudden and noticeable rise in respiration, followed by a more gradual increase in both the depth and frequency of breathing. During the onset of exercise, even before chemical signals are released, the cerebral motor cortex becomes more active, sending neural signals to the respiratory center. This neural activation is responsible for the initial spike in respiration.