# Characteristics of Changes in Contractile Properties of Muscle after Anaerobic Exercise
## 4 Discussion
In addition, small changes were observed in the Tc parameter (1%). As suggested by the authors [24], the decrease in Dm after the Wingate test reflected a swelling response, elevated intracellular water volume, and also heightened passive muscle stiffness induced by anaerobic exercise. Moreover, an increase in the Td parameter illustrated a longer reaction to the stimulus, and an increase in the Tc indicates a reduction in muscular contractile force due to muscle fatigue [31]. Within the study group, the Tr and Ts parameters in the rectus femoris muscle were also prolonged (Tr 39.23%, Ts 24.32%). This could stem from the involvement of the rectus femoris, which along with the hip flexors and adductors, perform the recovery function during the pedaling movement [6], and this may have translated into greater fatigue of this muscle. The reports of [PERSON] et al. [23] also seem to support the fact that, in many studies, muscle fatigue is typically linked with heightened time variable values. However, in the other study [23], the opposite situation was observed, because there was a significant decrease in the parameters Td, Ts, and Tr after the RSA test, along with an increase in the parameter Dm in the rectus femoris muscle for both the dominant and non-dominant leg. In turn, after the ultra-endurance triathlon [6], almost no changes in Tr, Ts, Tc, and Dm in rectus femoris were observed, and only shortening of the Td parameter was found. However, the authors explained that the rectus femoris muscle is crucial predominantly during the cycling phase, while its importance diminishes during running. Increased Td and the accompanying decrease in Ts were also observed in the gastrocnemius lateralis and gastrocnemius medialis muscles, while a significant decrease in the Tc occurred only in the soleus muscle. Correlation analysis revealed a notable connection between anaerobic endurance parameters and changes in individual muscle contractility parameters. The analysis shows that most of the changes (indexes of change) in muscle contractility parameters correlate negatively with Wingate test performance, which means, among other things, that the lower the power generated by an individual, the longer the contraction and relaxation times. No relationship was shown between the Dm parameter and most of the muscles tested, except for the gastrocnemius medialis for which this relationship was also negative. Therefore, it can be concluded that the participant's level of anaerobic endurance affects the level of changes in muscle contractility parameters after anaerobic exercise. This conclusion, of course, requires further research to characterize these compounds in detail. A limitation of the presented study is connected to the characteristics of the subjects. First, the research group consisted of only one gender. It limits the comparison between genders. Second the sample size is small. However, it was necessary to have a group of 20 participants to identify an interaction with an effect size of 0.86, with a significance level of 0.05. In addition, although all participants were described as active, differences in lifestyle and the presence of prior injury or medical conditions could have affected the results. Furthermore, only one anaerobic exercise was assessed, and the study was conducted once without testing the data collection. Furthermore, the high reliability of TMG has been confirmed for Tc, Dm, and Td parameters, while parameters Ts and Tr have poorer reliability [2]. In addition, there is no confirmed reliability for all the muscles we tested. Last, the time between coming off the cycloergometer and the end of the TMG measurement of the first and last muscle was not measured.