## 3 Results  
Figure 2 illustrates the description of the BP exercise movement and its different phases based on barbell position, velocity and acceleration. Based on power outcomes, the BP exercise movement can be divided into four different phases. During phase 1, there is negative vertical acceleration and velocity of the barbell, resulting in positive mechanical power (concentric). However, it has been observed that the movement of the barbell is due to the attraction of gravity rather than the concentric action of elbow flexors and shoulder extensors. Phase 2 is characterised by a positive acceleration combined with negative velocity, which indicates the performance of eccentric mechanical power and, subsequently, the eccentric mechanical work of the elbow extensors and shoulder flexors. During phase 3, there is a positive acceleration combined with positive velocity, signifying the performance of the elbow extensors and shoulder flexors, generating concentric muscle power. Finally, phase 4 is characterised by a negative acceleration with a positive velocity, which would involve the eccentric muscle power of the elbow flexors and shoulder extensors. However, it is observed that the movement of the barbell is mainly due to the attraction of gravity, not to the muscle action, although muscle activity acts partially in the development of the action. Table 1 shows the duration of each intensity interval and its CV for the different phases of the BP exercise. In all phases, interval 1 has a shorter duration than interval 2, and interval 2 has a shorter duration than interval 3, demonstrating a clear progression in duration as the load increases. Table 2 presents the comparative analysis between the different intensity intervals for V\({}_{\text{MAX}}\), V\({}_{\text{MEAN}}\), A\({}_{\text{MAX}}\) and A\({}_{\text{MEAN}}\) during the eccentric phase (P2) of the BP exercise. The results of the repeated measures ANOVA revealed significant differences among intensity intervals in V\({}_{\text{MAX}}\) (\(p<0.001\), \(\eta\)p2 = 0.716), V\({}_{\text{MEAN}}\) (\(p<0.001\), \(\eta\)p2 = 0.702), A\({}_{\text{MAX}}\) (\(p<0.001\), \(\eta\)p2 = 0.797) and A\({}_{\text{MEAN}}\) (\(p<0.001\), \(\eta\)p2 = 0.440). Pairwise comparisons showed that V\({}_{\text{MAX}}\) and VMEAN were significantly greater during interval 1 compared to interval 2 (V\({}_{\text{MAX}}\): \(p<0.001\), g = \(-0.87\); V\({}_{\text{MEAN}}\): \(p<0.001\), g = \(-0.12\)) and interval 3 (V\({}_{\text{MAX}}\): \(p<0.001\), g = \(-1.60\); V\({}_{\text{MEAN}}\): \(p<0.001\), g = \(-1.36\)). Likewise, V\({}_{\text{MAX}}\) and V\({}_{\text{MEAN}}\) were significantly higher during interval 2 in comparison with interval 3 (V\({}_{\text{MAX}}\): \(p<0.001\), g = \(-1.00\); V\({}_{\text{MEAN}}\): \(p<0.001\), g = \(-0.14\)). Similarly, A\({}_{\text{MAX}}\) and A\({}_{\text{MEAN}}\) were significantly greater during interval 1 compared to interval 2 (A\({}_{\text{MAX}}\): \(p<0.001\), g = 1.28; A\({}_{\text{MEAN}}\): \(p=0.002\), g = 0.36) and interval 3 (A\({}_{\text{MAX}}\): \(p<0.001\), g = 1.98; A\({}_{\text{MEAN}}\): \(p<0.001\), g = 0.55). A\({}_{\text{MAX}}\) was also significantly higher during interval 2 compared to interval 3 (\(p<0.001\), g = 1.06); however, there were no differences in A\({}_{\text{MEAN}}\) when intervals 2 and 3 were compared (\(p=0.131\), g = 0.22).