In the scientific field of basketball, salivary T, C and T:C are the most investigated and adopted markers to monitor hormonal responses to given loads during different typologies of training and matches (Moreira et al., 2013; Nunes, Crewther, Viveiros, et al., 2011; Sansone et al., 2019). An analysis of these markers is indicated as an essential method to determine the balance between anabolic and catabolic processes (Kamarauskas & Conte, 2022a), allowing to evaluate the process of training and recovery in basketball. In general, an increase in T levels indicates an appropriate recovery, whereas decrease in T levels and increase in C levels represents a possible risk of overtraining, non-functional overreaching and reduced performance (Coutts et al., 2007). Previous investigations, assessing changes in hormonal responses showed that the analysis of salivary markers could be used as valuable monitoring tool in basketball. However, a more detailed analysis of hormonal responses in combination with load measures and well-being variables in different basketball populations, during different phases of the season, could provide basketball coaches the benchmarks of load, well-being, and hormone measures. Moreover, there are no findings, if changes in load measures, and well-being variables can influence changes in hormonal responses, which would indicate if hormonal levels of basketball players are affected by changes in other measures. Such findings would allow to understand if measures of load variables can be used to anticipate changes in hormonal responses. The research described in this doctoral dissertation includes four scientific studies, addressing differently designed but related research questions. The assessment of weekly fluctuations in hormonal responses in different basketball populations (i.e., semi-professional and professional, male players), during different phases of the season (i.e., pre-season and in-season) were investigated in study 1 (Chapter II), study 3 (Chapter IV), and study 4 (Chapter V). The second study question, a comparison of weekly changes in hormonal responses in relation to changes in load measures and well-being between European- and national-level professional, male basketball players was investigated in study 4 (Chapter V). Finally, the last study question of this research, investigating relationships and associations between weekly changes in hormonal responses and weekly changes in load measures and players’ well-being during different phases of the season in different basketball populations were investigated in study 1 (Chapter II), study 2 (Chapter III), and study 3 (Chapter IV). The methodological design of all four investigations of this research was observational. Only semi-professional (Chapter II) and professional (Chapter III; Chapter IV; Chapter V), male basketball players were selected as participants of this research. The inclusion criteria of participants in all four studies were based on the attendance, and only participants with attendance of ≥75% of total training sessions and matches combined, were included for the final analysis of each study. The monitoring periods of all studies described in this research were implemented, following the actual schedules of pre-season or in-season phases of investigated teams, without applying any experimental changes for the research purposes. Data was collected during strength and conditioning (except weight room sessions), basketballspecific on-court training sessions, and depending on the study, during in-season official matches or pre-season friendly matches. During the data collection, saliva samples were collected for the analysis of changes in levels of T, C, and T:C (Andre et al., 2018; Arruda et al., 2018; Nunes et al., 2014). External load measures (PL and PL·min-1 ) were monitored using triaxial accelerometers ClearSky T6 (Catapult Innovations, Melbourne, Australia) sampling at 100 Hz to calculate instantaneous movement demands (in arbitrary units, AU) (Fox et al., 2020b; Scanlan et al., 2014). Internal load measures were monitored using the sRPE method (Foster, 1998), and HR measures (Berkelmans, Dalbo, Kean, et al., 2018). The sRPE method and total duration (min) of each training session and match were used together to calculate sRPE-load in AU. Subsequently, these data were used to calculate weekly monotony and strain variables (Foster, 1998). HR was measured by Polar H10 chest-worn straps (Polar Electro; Kempele, Finland), and subsequently collected and processed via OpenField software (version 1.18, Catapult Innovations; Melbourne, Australia), to calculate SHRZ load (AU) (S. Edwards, 1994), and %HRmax (Berkelmans, Dalbo, Kean, et al., 2018). HRmax of each participant was determined as the peak HR attained during a maximal 30-15 Intermittent Fitness Test performed on a basketball court at the beginning of the monitoring period (Buchheit, 2008). The maximum HR attained during this initial testing was updated to a new peak value if it was superseded by HR responses recorded during training sessions or friendly matches throughout the monitoring period (Berkelmans, Dalbo, Fox, et al., 2018). An established well-being questionnaire was used to assess perceived fatigue, sleep quality, general muscle soreness, stress, and mood on a five-point Likert scale (scores from 1-5) (Conte et al., 2018). Overall well-being was then calculated by summing the scores across each item assessed (Conte et al., 2018). Ethical approval was obtained from the Kaunas Regional Research Ethical Committee review board (No. BE-2-97). The first purpose of this research was to assess weekly fluctuations in hormonal responses during different phases of the season, in different basketball populations. Three studies of this doctoral dissertation were aiming to assess weekly fluctuations in hormonal responses during a 4-week period of the in-season phase in semiprofessional, male players (Chapter II), across a 5-week pre-season phase in professional, male players (Chapter IV), and across a 5-week pre-season phase of European- and national-level professional, male basketball players (Chapter V). The results of three investigations showed different findings on weekly fluctuations in hormonal responses. In study 1 (Chapter II), a congested in-season phase with a constant external load and decrease in internal load measures was found causing a decrease in T and C levels, and no changes in T:C ratio. As T:C remained stable across a monitoring period, a possible explanation of imbalance between load and recovery negatively affecting T levels was rejected. A negative effect on T levels most possibly occurred due to the constant losing in official matches, resulting in a lower willingness to compete and decreased T levels (Mehta & Josephs, 2006). Contrary, a constant losing in matches did not cause an increase in C levels, which was found decreasing towards the end of the investigated period. During the in-season phase, levels of C were previously shown to increase due to a higher accumulated physical stress (Moreira et al., 2011; Nunes et al., 2014). Therefore, as monitoring period of study 1 (Chapter II) was in the middle of the in-season, a possible explanation of decreased C levels might be a lower accumulated physical stress than in other investigation, which reported an increase in C levels in the end of the in-season phase (Moreira et al., 2011). Differently than during the in-season phase in semi-professional, male basketball players, study 3 (Chapter IV) and study 4 (Chapter V) provided inconsistent findings of hormonal responses during the pre-season phase in professional, male basketball players. An increase in T and T:C levels, and no changes in C levels during the pre-season phase were found in two European-level teams (Chapter IV). Inversely, no changes or differences in T levels across the pre-season phase, but higher C and lower T:C levels in the beginning of the pre-season phase were found for the European-level team, when compared to the national-level team and other weeks of the pre-season phase (Chapter V). A different findings emphasize the importance of load management process during the pre-season phase, to maintain an appropriate balance between anabolic and catabolic processes (Alba-Jimenez et al., 2022). The main conclusion of the assessment of weekly fluctuations in hormonal responses during the in-season and pre-season phases in semi-professional and professional, male basketball players indicates the usefulness of monitoring hormonal responses in basketball to evaluate changes and maintain an appropriate balance between anabolic and catabolic processes across different phases of the season. The second purpose of this research was to compare two professional, male basketball teams, preparing for the season at different playing levels, i.e., Europeanand national-level (Chapter V). The main findings of this investigation showed different load periodization strategies, depending on playing level. European-level team, preparing for the congested season schedule had increasing training load, while national-level team, preparing for a less congested in-season phase had decreasing training load towards the end of the pre-season phase. The explanation of this dissimilarity is most possibly related to the differences in the upcoming in-season phase, which teams were trying to replicate during the pre-season phase. When considering hormonal responses, these differences in load periodization, induced no differences between teams in T levels, while European-level team had a higher C and T:C levels at week 1 of the pre-season phase. A higher European-level team C and T:C ratio levels in the beginning of monitoring period, resulted in an overall higher level of C and T:C across the pre-season phase. The main conclusion of the assessment of differences between European- and national-level professional, male basketball teams during the pre-season phase is that load periodization in preparation to play at a higher level and more congested in-season schedule, has a negative impact on the balance between anabolic and catabolic processes. The last goal of this doctoral thesis was to quantify the relationships between weekly changes in hormonal responses and weekly changes in load variables, and players’ well-being, during different phases of the season in different basketball populations. The relationships between weekly changes in T, C and T:C responses and weekly changes in external and internal load, and well-being variables during the inseason phase in semi-professional, male basketball players were investigated in study 1 (Chapter II). Relationships between separately and jointly considered weekly changes in load measures and hormonal responses during the pre-season phase in professional, male basketball players were examined in study 2 (Chapter III). The associations between weekly changes in hormonal responses and load measures with weekly changes in well-being during the pre-season phase in professional, male basketball players were determined in study 3 (Chapter IV). The main findings of study 1 (Chapter II) showed non-significant, trivial-to-moderate relationships between weekly changes in hormonal responses and weekly changes in load and well-being variables during the in-season phase in semi-professional, male basketball players. Similarly, study 2 (Chapter III) showed that neither separately, neither jointly considered changes in load measures are not influencing changes in weekly hormonal responses, during the pre-season phase in professional, male basketball players. Additionally, study 3 (Chapter IV) showed only negative and weak associations between weekly changes in well-being and weekly changes load measures, and no associations between weekly changes in well-being and weekly changes in hormonal responses, during the pre-season phase in professional, male basketball players. The findings of all three studies suggest that other measures than investigated in these studies or combination of them might be influencing weekly fluctuations in hormonal responses. Moreover, these findings suggest that all investigated measures might provide a unique insight about training and recovery process in basketball and should be separately used for the monitoring of basketball players. The main conclusion of the quantification of relationships and associations between weekly changes in hormonal responses, load measures, and well-being variables indicates that these measures are not influencing weekly changes in between each other and that weekly fluctuations in these variables might be induced by other physical, physiological, psychological measures or combination of factors.