## 5 Discussion  
This study aimed to analyze acute changes in muscle mechanical properties of the triceps brachii long head after the bench press exercise performed at different external loads and with different intensities of effort along with power performance in male strengthened athletes. The results showed that the external load used during the bench press had an overall effect of increasing muscle tone after the performed sets but not for stiffness. In addition, there was a significant decrease in peak and average barbell velocity during the bench press in a set at 70% 1 RM compared to the first two repetitions in a set at 70% 1 RM UF. However, the reported changes in muscle tone did not significantly coincide with the significant decrease in power performance. First, we have to state that this study showed a \"poor\" to \"excellent\" intraclass coefficient for elasticity (decrement), relaxation time, and creep, while for stiffness and muscle tone, it was \"good\" to \"excellent\" (Table 1). Therefore, it seems that the Myoton device is inappropriate in assessing changes in elasticity, relaxation time, and creep following resistance exercises. Consequently, we recommend that future research pay special attention to checking and reporting the reliability of measurements made via the Myoton. The reported changes in muscle tone partially confirmed our initial hypothesis about the impact of external load used on differences in mechanical muscle properties. After the set at 50% 1 RM, no significant changes were noted in muscle tone or stiffness. Only after the set at 70% 1 RM and 90% 1 RM was a statistically significant immediate increase in muscle tone noted. The same trend was noticed in the case of stiffness; however, it did not reach the level of significance. Previous studies found that increases in muscle tone and stiffness have been associated with fatigue and decreased performance [32; 40; 41; 42]; therefore, this might indicate that some degree of fatigue has occurred. Interestingly, despite significant differences in volume compared to other sets (2 vs. \(\sim\)13 repetitions), the changes after the set at 70% 1 RM UF had a similar yet insignificant trend. It is also interesting that a similar level of muscle tone after the set at 90% 1 RM and at 70% 1 RM UF was noted. Therefore, it could be speculated that other mechanisms were responsible for these changes. Muscle tone might depend on both active (dependent of neural activity) and passive (independent of neural activity) muscle components. It seems that the reported increase in muscle tone after the bench press set at 70% 1 RM and 90% 1 RM may be related to the increase in neural drive. The comparable level reached after the set at 70% 1 RM UF could be caused by the rise of intramuscular pressure because of increased intracellular fluid due to the intense effort [43]. Nevertheless, it cannot be ruled out that if a higher volume were used, e.g., several consecutive sets or sets until failure, a significant change in the stiffness or a higher increase in muscle tone would occur. Furthermore, it is worth noting that the muscle tone level before the 70% 1 RM UF was slightly higher, which may have been a residual from the set at 90% 1 RM, indicating some degree of fatigue. This potential state could be manifested by a significant decrease in barbell velocity observed during the first two repetitions in the set at 70% 1 RM UF compared to the set at 70% 1 RM. A decrease in velocity has been previously revealed as an indicator of neuromuscular fatigue during resistance training [44]; thus, the results suggest that substantial fatigue has occurred. They indicate that three subsequent sets of two repetitions at 50, 70, and 90% 1 RM, respectively, with a 4 min rest in between, impair power performance and increase muscle tone among resistance-trained males. This trend of simultaneous muscle tone increase and performance impairment may suggest that muscle tone may be a sensitive marker for detecting acute fatigue.