# Evaluation of Thorax Diameter Changes through Trunk Morphology and Different Running Intensities
## 4 Discussion  
In the present study, the variations in thorax expansion through different running intensities and various morphology groups were evaluated using thorax cross-sections recorded by a motion capture system. Our results have partially confirmed the first hypotheses of the study as it was found that the three thorax cross-sections increased when the intensity of the exercise was raised, especially the mediolateral and anteroposterior cross-sections. However, there were no significant differences in thorax expansion in any of the cross-sections between morphology groups when compared at the same running intensity. Although the effect of the thorax morphology was not significant, some influence of it was seen in the changes in the anteroposterior cross-section. The subjects with a flatter thorax (group 1 and group 2) behaved differently than group 3 (deeper thorax) because they did not increase the anteroposterior cross-section when they passed from medium to highest intensity. It is important to highlight the relevance of our research as a new easy-to-use and ecological approach. This method has been developed for assessing breathing mechanics with applications to sports performance and the assessment of patients with respiratory diseases. In addition, it is important to mention that the results obtained in this study are related to the sample characteristics: young males with low BMI. We have found that the three cross-sections had a larger expansion of the thorax when subjects were running at an intensity of 85% HRR and a smaller expansion at 45% HRR. These results agree with those obtained by [PERSON] et al. (2005), where they used OEP during cycling at different intensities, concluding that inspiratory volume increases with the increase of intensity [38]. We have found that the IP of the craniocaudal and anteroposterior thorax cross-sections showed a smaller change from 45% to 70% HRR than from 70% to 85% HRR. However, in the mediolateral cross-section, a bigger change took place from 45% to 70% HRR compared to the change between 70% and 85% HRR, reflecting a quicker change during low- to mid-intensity exercise than during the highest intensity. These results are expected from a physiological point of view [3]. During low- to mid-intensity exercise, the elevation of the lower ribs produced by the contraction of the diaphragm increases the mediolateral cross-section of the thorax, followed by the elevation of the sternum and the upper ribs during high-intensity exercise enhancing the anteroposterior cross-section [3]. [PERSON] and [PERSON] (2012) documented differences between the movement of the thorax during quiet breathing and deep breathing in different positions (sitting and standing) without performing any effort [9]. They observed that the expansion of the thorax varies when the breathing pattern is modified [9]. It has also been demonstrated that body posture affects thorax volume variations during breathing due to the position of the ribs, the diaphragm, etc. [28]. This can be the reason for the discrepancies between our data and