Internal training load and its longitudinal relationship with seasonal player wellness in elite professional soccer
Introduction
Monitoring internal training load has been used extensively and well discussed in sports, especially in team sports [1]. Additionally, compared to internal physiological measures, such as heart rate (HR) and rate of perceived exertion (RPE), other measures of physiological status are less known. Recent literature has reported the use of the Hooper index [2] as a reliable method for the monitoring of athlete wellness providing further information concerning the detail of player fatigue, stress, muscle soreness and sleep perception. The Hooper index has recently been utilized to monitor player wellness during a 4-day FIFA international futsal tournament [2] in addition with a 2-month study on cycling performance [3]. However, apart from the aforementioned studies, the relationship between use of the Hooper index and session-RPE is limited amongst the research. One investigation observed no association between the Hooper index and RPE [4], however, further research is needed in this subject to validate the findings further.
Recent literature using team sport players competing in one game microcycle have shown that internal training load might be more intense towards the beginning of the microcycle as a way to ensure fatigue is minimal close to competitive match play [5], [6], [7] and a one-month mesocycle [8]. However, competing in 2-game microcycles occurs often in team sports such as soccer, when teams are more successful based on their need for domestic and European competition [6], [9]. A recent study also suggests that there are evidences of a negative impact of a longitudinal fixture congestions cross the season [10]. Only a few studies have so far investigated the quantification of training of microcycles varying for scheduled matches focusing on the external load, i.e. distance covered per training unit [6], [11], [12].
The effect of game and training load on fatigue have been also analyzed in the context of soccer [13], [14]. The immediate effect of a game is to reduce the maximal voluntary contraction and increase the muscle soreness [15]. Decreases in repeated sprint ability after the game is also commonly observed [16], [17]. However, the extension of the fatigue effect after game or training seems to be influenced by the competitive level in which elite recover faster than amateur players [15].
The daily training load may also constrain the perception of fatigue and the risk of illness and injury [18]. In a study conducted in elite soccer players it was found that ratings of fatigue were sensitive to fluctuations in acute total high-speed running distance accumulation [19]. Moreover, the high perception of leg muscular effort after high training volume can impair the improve of physical fitness variables [20]. The quality of sleep and the stress are also sensitive to the training volume [21].
Although the abovementioned research has enhanced our understanding of the variation of fatigue in different periods, namely identifying some decreases in performance variables [9] and the association of training load with quality of life variables, we believe that is still necessary to cross in a single study the variables of training load, perception of fatigue, stress, muscle soreness and stress and analyze such variance in different types of week. Such information would be of practical and theoretical value for coaches and researchers, respectively, as it may help coaches tailor training sessions with the aim of minimizing fatigue and lead to the player's perceptions. Therefore, as a result of the limited investigations in this area, the aim of this study was to i) to analyze the microcycle variance using the Hooper index scales amongst positional roles (1 vs 2 games per week), and ii) study the association between internal training load (ITL) and Hooper index scales.
Section snippets
Participants
Thirty-five professional soccer players from the Portuguese premier league participated in this study (25.7 ± 5.0 years; 182.3 ± 6.4 cm; 79.1 ± 7.0 kg). Two inclusion criterions were selected to analyze the variance of HI and ITL between microcycles: i) ensure regular participation in the majority of training sessions (80% of weekly training sessions); ii) possesses medical clearance at the beginning of the microcycle to participate in full training. The study of HI levels between weeks with one or two
Results
Analysis of variance found that DOMS (p = 0.001; ES = 0.087), fatigue (p = 0.001; ES = 0.060), Hooper index (p = 0.045; ES = 0.034) were higher in weeks with two matches and stress (p = 0.003; ES = 0.050) and internal training load (p = 0.001; ES = 0.195) were higher in weeks with one match. DOMS, fatigue and HI were 7.42%, 6.35% and 2.51% higher in weeks with two matches than with one match, respectively. In the other hand, stress and ITL were 5.49% and 25.49% higher in weeks with one match, respectively.
Discussion
The primary aim of this investigation study was to assess positional playing differences on ITL, session-RPE and wellness across two-different training microcycles (1 vs. 2 competitive games). Furthermore, the investigation aimed to examine the relationship between ITL and psychophysical monitoring levels (i.e. Hooper's Index) across the entire season. To the authors knowledge, this is the first study investigating the variance of HI and ITL across playing positions within different microcycles
Conclusion
Microcycles with two official matches revealed significantly greater values of DOMS and fatigue scores. In the other hand, higher values of internal training load were found in weeks with one match. Relationship tests between ITL and HI scores have revealed significant and negative small-to-moderate correlations in the weeks with two official matches but not in the weeks with only one match. Finally, HI scores and ITL differed significantly from position to position, thus suggesting that the
Acknowledgements
The authors would like to thank to BenficaLab and the soccer players for their participation. This work was supported by the FCT project PEst-OE/EEI/LA0008/2013.
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