Monitoring mood state to improve performance in soccer players: A brief review

Introduction Psychological aspects of sport are key in maintaining athlete motivation and make a difference in competitive outcomes. Adjustments to training may be necessary according to athletes’ emotional state. Therefore, it is important to assess and quantify mood states throughout the season in team sports, including among soccer players. The Profile of Mood States (POMS) is a widely used questionnaire that assesses emotional states characterized by positive or negative feelings and can be administered repeatedly to assess changes in mood state. This review aims to assess and summarize the current literature on mood state variation in soccer players with a specific focus on training loads, training modalities, and competitive performance. Methods A literature search was systematically conducted and resulted in 156 records. After removing duplicates, items with irrelevant titles and abstracts were screened out, and full texts were then screened for relevance and compared with inclusion and exclusion criteria. The remaining 37 articles were included in the final qualitative synthesis. Results POMS scores were related to variability in training load, intensity of the training period, modality of training exercises, competitive performance and time of day in soccer players. Common recommendations include monitoring the mood state of soccer players during training sessions, matches, and throughout training periods to detect early signs of psychological disturbance and aid in optimizing high-level training performance. Conclusion The POMS allows for monitoring of players’ psychological state, providing coaches with data to aid in adjusting acute program variables according to players’ psychological states and improve performance. Results offer practical support for the use of a simple POMS measurement as part of an overall program to monitor the players’ psychological states. Results also highlight how training choices (i.e., load and exercise modality) and competitive performance are related to mood states (i.e., tension, anger, confusion, depression, fatigue, and vigor).


Introduction
Optimization of sport performance is linked to multiple factors such as physical, technical, tactical, and cognitive skills. The importance of mental health as a factor in sport performance is becoming increasingly recognized, including among soccer players (Soylu et al., 2021). Mental health is a concept that includes emotional, psychological and social states of athletes and affects the way they feel, react, and behave (Souter et al., 2018;Russell et al., 2020). Among the many dimensions of mental health is mood state which may change in response to the daily and periodic challenges that soccer players face (Selmi et al., 2017). Additive stressors from soccer players' personal lives, wellbeing, and sport training can influence mood state (Yagmaee, 2021). It is clear that soccer performance is closely linked to mental health in general and to mood state specifically (Yagmaee, 2021).
It is well known that in the field of sport, mood state is affected by psychophysiological responses (Soylu et al., 2021) and influenced by various factors such as training modality (Selmi et al., 2017), training load (TL; Beykzade et al., 2011;Watson et al., 2017;Botelho et al., 2022), competitive performance (Filaire et al., 2001;Casanova et al., 2016) and motivation and concentration of athletes during training (Aydi et al., 2022). Therefore, sport psychologists have sought to develop and validate reliable tools and inventories to assess athletes' mood states (Filaire et al., 2001;Saidi et al., 2020). In fact, the validated Profile of Mood States (POMS) questionnaire has been widely used to assess mood state in different sport situations such as during individual training sessions, throughout training periods, and before or after competitions (Miranda et al., 2013;Saidi et al., 2020;Selmi et al., 2020). Additionally, this tool has been widely used to explore the relationship between training modalities, TL and athletes' psychological state (Lovell et al., 2010;Aydi et al., 2022). For that reason, it is suggested that psychological state should be assessed during training to control and prevent negative mood states that are related to training intensity and exercises' modalities.
Increased TL during intense training periods in soccer is associated with a lack of concentration, negative feelings, uncertainty, and mental fatigue (Smith et al., 2016), which are reflected by mood and behavior changes, increased anxiety and aggressiveness, indifference, irritability, and sleep disturbance (Selmi et al., 2020). Sleep quality is a key and vital factor which can affect athletes' mood state (Paryab et al., 2021). In fact, sleep loss is detrimental to vigor and attention and increases fatigue, confusion, depression, and tension (Benjamin et al., 2019(Benjamin et al., , 2020. Moreover, sleep is essential to maintain adequate recovery and stress tolerance among soccer athletes, and needs increase with TL (De Morais Ferreira et al., 2022). Because of the potential implications of psychological aspects of sport, a great deal of attention has been focused on the impact of high TL on mood. Several studies have confirmed that mood disturbances increase during heavy training periods (Smith et al., 2016;Botelho et al., 2022) alongside physiological variations (Filaire et al., 2001;Silva et al., 2008). Based on this body of work, Smith et al. (2016) suggested that negative affective responses and reduced performance may be related to physical fatigue accumulation, while positive affective responses during the taper period were associated with positive physiological changes and higher performance (Filaire et al., 2001;Beykzade et al., 2011). This is likely due to fatigue reduction and recovery during taper which allow for improved physical performance (Schmikli et al., 2011).
Additionally, mood state variation has been associated with performance achievement or failure (Jones et al., 2010;Miranda et al., 2013;Casanova et al., 2016;Picoli and Bueno, 2022). Therefore, mood regulation strategies may be beneficial for the competitive performance among soccer players (Hashim et al., 2011;Bijukumar, 2021). Mood regulation is associated with training modalities and player motivation (Selmi et al., 2017). In fact, verbal encouragement, a form of motivational training, improved mood state and resulted in greater self-reported physical enjoyment among young soccer players (Aydi et al., 2022). Using the POMS to monitor players' mood state may allow the technical staff of the soccer teams to better adapt TL, improve programming and select motivational training exercises to maximize performance via improved mood state.
This brief review summarizes the current literature on mood state variation in soccer players in the following areas: (1) TL and training period; (2) exercises modality; (3) competitive performance; and time of day. Additionally, a discussion of the impact of training on mood state is presented. Practical applications and future research are suggested.

Search strategy
This review included studies that examined the effect of training on mood state within soccer players. The literature search was performed using PubMed, Scopus, Web of Science, and Google Scholar and included articles published until August 10, 2022. The oldest article retrieved was published in 2001. Moreover, we performed manual searches of relevant journals and reference lists obtained from published articles. The following English terms and key words were searched using Boolean operators: "mood state" AND "soccer" combined with the key words "training load, " "training period, " "training exercise" and "performance"(i.e., "mood state" AND "soccer" AND "training load, " "mood state" AND "soccer" AND "training period, " "mood state" AND "soccer" AND "training exercise, " and "mood state" AND "soccer" AND "performance"). The inclusion criteria for these articles were: (1) the original studies were published in English; (2) data concerning training load, training period, exercise training or performance; (3) players included soccer players; and (4) studies examined mood state. The exclusion criteria were: (1) studies that included sports other than soccer; (2) studies that did not include any of the parameters evaluated in this review; and (3) reviews, commentaries, interviews or expert opinions, posters, or book chapters (Figure 1).
Two authors independently extracted and reviewed study data to verify if a given study met the inclusion criteria. Disagreements between the two authors on the inclusion criteria were resolved by a third author with experience in the field.

Definition and measurement of mood state
According to Lane (2001), mood is a set of sensations varying in intensity and duration. Chennaoui et al. (2016) reported that emotional mood contributes to an athletes' likelihood of success or failure in relation to training. This concept refers to the change in emotional state. Athletes may think of this dichotomously and report Frontiers in Psychology 03 frontiersin.org being in a good or bad mood characterized by overall positive or negative feelings, respectively (Selmi et al., 2020). To identify practical assessments, researchers examined various psychological dimensions related to training that require less technology such as mood state questionnaires which have been actively researched in recent years (Saidi et al., 2020;Aydi et al., 2022;Picoli and Bueno, 2022). The profile of mood states (POMS) is a selfreport questionnaire comprised of 65 items assessing seven mood states subscales (i.e., tension-anxiety, anger-hostility, confusionbewilderment, depression-dejection, fatigue-inertia, vigor-activity, and interpersonal relationship; Table 1), with the interpersonal relationship subscale often being eliminated from measurement by researchers. Each item is rated on a 5-point Likert scale from 0 (not at all) to 4 (extremely) in response to questions such as "How are you feeling right now? (Aroian et al., 2007). The six subscales of POMS can be combined into a total mood disturbance (TMD) score by summing the (T) scores for the five negative mood subscales and subtracting the T score for positive mood state and adding a constant of 100 in order to prevent negative numbers. Terry et al. (2003) published guidelines for the definition of each emotional state assessed by the POMS. According to this work, tension is characterized by sensations such as nervousness, apprehension, worry and anxiety. Anger is characterized by feelings that vary in intensity from annoyance or mild aggravation, fury, and irritation. Confusion described feelings of indecision associated with a decreased ability to control alertness and emotions. Depression is associated with a negative self-concept characterized by themes such as disappointment, deficiency, ineffectiveness, and self-blame. Fatigue is characterized by perception of mental and physical fatigue. Vigor represents the state of well-being, power, excitement, concentration, alertness, vitality, and strong ability to execute physical and mental effort. Finally, interpersonal relationships describe more of a trait than a specific state, but a strong score on this subscale is considered to indicate positive emotional state (Terry et al., 2003). These dimensions can be expressed in terms of state or trait depending on whether the instructions accompanying the form guide the participant to concentrate on their feelings at the moment, throughout the day or week of the assessment, or their usual feelings.
Some researchers have distinguished between high performers and low performers based on their pre-competition mood states (Filaire et al., 2001;Casanova et al., 2016). These studies reported that positive emotional state and successful athletic performance are strongly correlated. Specifically, the players who present lower tension, depression, anger, confusion and fatigue scores and higher vigor Flowchart describing the study selection process.
Frontiers in Psychology 04 frontiersin.org scores generally have more competitive success than players with the opposite profile as assessed by the POMS questionnaire. This positive profile has been called the "iceberg" profile (i.e., high vigor score and low scores for depression, tension, fatigue, confusion and anger) (Filaire et al., 2001;Casanova et al., 2016).

The relationship between training loads, training periods, and mood state variation
During high-intensity training periods characterized by heavy TLs, athletes have usually reported significant mood changes (Filaire et al., 2001;Lovell et al., 2010;Picoli and Bueno, 2022). For example, Filaire et al. (2001) showed that mood disturbance increased progressively with higher TL. It has also been shown that acute fatigue during intense training periods was associated with worse mood state and decreased vigor (Lovell et al., 2010;Saidi et al., 2020). Similarly, Fields et al. (2021) reported higher intensities during soccer preseason were associated with more negative mood scores (i.e., anxiety, anger, depression, confusion, fatigue), while indicators of positive mood states (i.e., vigor) decreased. These results are in line with those reported by Filaire et al. (2001), which showed that mood disturbance increased with the training stimulus. Amstrup et al. (2002) examined the effects of sports season on mood states and found no change in POMS scores during the pre-season period. However, vigor decreased and fatigue and depression increased from the end of pre-season to mid-season. Additionally, Miranda et al. (2013) studied changes in mood across of10 weeks of training in young soccer players. This study showed that as training intensity increased throughout the training period, the mood state became more negative (Miranda et al., 2013). However, Silva et al. (2008) reported that POMS scores were stable after12 weeks of high training intensity, suggesting that athletes' mood states may be more vulnerable during extended periods of intense training.
The relationship between overtraining and mood state has also been investigated. Schmikli et al. (2011) reported a significant increase in depression and anger subscale scores and total mood disturbance (TMD) with overreaching in soccer players. Lovell et al. (2010) found that mood state shifted from more positive to more negative as the competitive season progressed, likely due to increasing TL and accumulating stress. Similarly, during a period of congested matches (10 games over 6 weeks) soccer players reportedly significantly increased fatigue, tension, anger and a decreased vigor compared to the non-congested period of match play (6 games over 6 weeks). They suggested that mood state disturbance is associated with increased physical and physiological load. Additionally, Botelho et al. (2022) showed significantly increased negative mood scores (i.e., tension, depression, anger, fatigue, confusion, and TMD) after7 weeks of intensive pre-season training in female soccer players, suggesting that training intensity increase may be associated with negative mood changes (Filaire et al., 2001). Results from these studies are consistent with the finding that substantial increases in training intensity may result in a decreased ability to concentrate and feelings of disorder, uncertainty, and mental fatigue (Djaoui et al., 2017). These changes in mood are also associated with poorer recovery state and well-being changes in soccer players (Selmi et al., 2020).
The tapering period, characterized by reduced training intensity, generally appears to have a positive effect on mood state. Beykzade et al. (2011) reported that after the tapering period, TMD, fatigue and depression decreased significantly compared to the beginning of the intense training period. Reducing the training intensity during the tapering period can produce a balance between effort and recovery which leads to mood regulation (Beykzade et al., 2011).
Regarding the study during Ramadan, the study by Baklouti et al. (2017) compared the effects of two small-sided game (SSG) training formats (4 × 4 min and 2 × 8 min) on mood state during Ramadan in male professional soccer players. The results indicated that Ramadan and not training increased subjective feelings of fatigue. Along the same lines, the study by Chtourou et al. (2011) which examined the effects of Ramadan fasting on RPE and mood state. They indicated that RPE and fatigue score were higher during Ramadan in comparison with before Ramadan.
Overall, results from studies using the POMS to assess mood state reveal that extended intense training is associated with more negative mood states, whereas periods of reduced training can be useful in restoring more positive mood state. However, short-term intense training may not negatively impact mood state. A summary of 13 studies examining the effects of both training intensity and periods on mood state variation is presented in Table 2.

Training exercises and mood state
Limited research has investigated how acute mood state changes with different training exercises in soccer. Those that have indicate   (Selmi et al., 2017). In fact, Selmi et al. (2018) assessed mood responses to high-intensity interval training (HIIT) in soccer players, with the POMS questionnaire administered immediately before and within 5 min after training. Results indicated a significant increase in negative mood scores (i.e., anxiety, fatigue, and global mood score) and decrease in vigor score. Selmi et al. (2017) also reported that physical small-sided games (SSGs) induced significant improvements in mood state in professional soccer players. In the same study, both HIIT and SSG sessions induced similar physiological responses; in contrast, HIIT resulted in mood disturbance highlighted by increased tension, fatigue and TMD scores, whereas SSGs provided mood balance. The stability of POMS scores in this study may be due to athletes' motivation during preferred exercise modalities (i.e., exercises using the ball; Selmi et al., 2017). Similarly, Oliveira et al. (2009) reported that fatigue scores increased following a HIIT session in female soccer players. Broodryk et al. (2017) examined the effect of an anaerobic fatigue test (Yo-Yo Intermittent Recovery) on cortisol levels and mood state in female semi-professional soccer players and found significantly increased cortisol, psychological fatigue and TMD and decreased vigor. Sparkes et al. (2018) found perturbed mood state for up to 24 h after intensive SSG during the competitive period in professional soccer. Exercise motivation is associated with positive mood in soccer players and may be achieved using specific drills such as integrating the ball during physical tasks or the use of verbal encouragement by coaches (Aydi et al., 2022). Specifically, Aydi et al. (2022) showed that technical circuit dribbling drills with verbal coach encouragement improved mood state highlighted by decreased scores on negative mood subscales and increased vigor. Together, these studies suggest that verbal encouragement is an effective method to improve mood or prevent mood disturbances during training. A summary of 5 studies investigating the relationships between exercise session characteristics and mood state variation is presented in Table 3.

Competitive performance and mood state
Previous studies have examined the relationship between mood state and performance using the POMS questionnaire (Filaire et al., 2001;Miranda et al., 2013). In fact, mood state in soccer is related to competitive performance in terms of win/draw/lose (Casanova et al., 2016). Studies with professional soccer players have shown that athletic performance can improve positive and decrease negative POMS subscale scores (Robinson and Howe, 1987;Filaire et al., 2001;Miranda et al., 2013). Furthermore, Silva et al. (2008) showed that when professional team presented an "iceberg" profile during the training program, with a fatigue score decrease from beginning to middle season, coinciding with the team's best performance during the season (50% of wins). However, decreased vigor score at the end compared to the beginning and middle of the season, corresponded with poor performance (33.3% wins; Silva et al., 2008). Similarly, Miranda et al. (2013) reported that the overall POMS score increased significantly in male youth soccer players after 10 weeks of training indicating greater TMD, and that the mood state disturbance was correlated with the team ranking in the championship. Mood state also appears to be related to match outcomes. Casanova et al. (2016) indicated that positive mood state (vigor) score increased after lost matches and anger score decreased after won matches during an official female association football tournament while "Iceberg" profiles were observed during all 5 matches regardless of outcome. Lowther and Lane (2002) indicated that vigor was associated with successful match performance and depression score were associated with poor match performance in a soccer team. Oliveira et al. (2009) examined the influence of match results on mood changes in professional female soccer players. They found more positive mood states among winners and more negative mood states among losers at the end of the matches, suggesting that overall mood state is related to match performance in female soccer players. Moreover, Dejongh et al. (2006) examined the relationship between in-season team performance and mood state in professional female soccer players. They showed that tension, depression, anger, and confusion scores were lower and vigor was higher when the team won indicating that poor performance was related to negative mood state in female players. In addition, Filaire et al. (2001) showed lower vigor scores when the performance of a professional male soccer team was below 50.0% wins. It is likely that competition success can lead to improved psychological states including more satisfaction, pleasure, and reduced anxiety, while the effects of defeat can produce poor wellbeing (Casanova et al., 2016). Alternatively, more negative mood state may decrease competitive performance. A summary of 6 studies regarding the relationship between competitive performance and mood state variation is presented in Table 4.

The effect of training on mood regulation
Mood regulation strategies may benefit athletic performance (Hashim et al., 2011). In fact, strong athletic performance among soccer players is associated with high positive mood scores and low negative mood scores (Hashim et al., 2011;Bijukumar, 2021). Indeed, researchers have revealed several mood regulation strategies for soccer players (Selmi et al., 2017;Bijukumar, 2021). For example, Hashim et al. (2011) compared the effects of two different relaxation techniques, known as progressive muscle relaxation and autogenic relaxation on the mood of young soccer players and showed that these relaxation techniques induced equivalent beneficial mood responses and can be used to regulate mood state (Hashim et al., 2011). Akimoto et al. (2003) studied the effect of acupuncture treatment on the mood state in 12 women soccer players during the competition period. The results indicate that acupuncture treatment has a positive effect on mood regulation with improved positive mood and reduced negative mood scores. Other less obvious mood regulation strategies may also be effective, such as choices in training programming. For example, Progressive Muscle Relaxation training (PMR)decreased mood disturbance, anger, tension, and fatigue scores in university students (Bijukumar, 2021) suggesting positive impacts on mood state. This may be a worthwhile strategy to examine among soccer players. Selmi et al. (2017) showed that SSG, a training exercise that soccer players found more enjoyable and motivating, provided better mood state regulation compared to HIIT, a less preferred training strategy, despite similar training intensities. Likewise, previous studies have shown that using motivational training exercises can reduce negative emotions and improve mood in soccer players (Hashim et al., 2011;Aydi et al., 2022). Therefore, implementing relaxation training and selection of preferred training exercises could help to regulate the mood state of athletes (Hashim et al., 2011;Bijukumar, 2021).  A summary of 4 studies examining the relationship between training and mood regulation is presented in Table 5.

Time of day and mood state
Mood state in soccer players is related to time of day and to training time (e.g., morning versus evening training) (Chtourou et al., 2012(Chtourou et al., , 2014Masmoudi et al., 2016;Irandoust et al., 2019;Hsouna et al., 2021;Masmoudi et al., 2021). In male youth soccer players, depression, RPE scores, Hooper Index, and stress were higher in the afternoon than the morning (Masmoudi et al., 2016). In some studies, training in the morning improved mood state (Masmoudi et al., 2016;Irandoust et al., 2019), whereas Masmoudi et al. (2021) showed that only depression and vigor scores, but not anger, confusion, fatigue, inter-relation, or TMD were significantly worse when training at 17:00 h compared to 08:00 h. Across these studies, exercise/training in the morning boosts physical performance and physiological status including perceived energy levels that may have positive feedback effects and perpetuate improved mood. These studies also indicated that morning activities may also confer improved mental health status and productivity throughout the day. Dietary patterns, especially periods of fasting like Ramadan, may be particularly important for time-of-day studies to consider since fasting could impact mood and performance. Chtourou et al. (2012) observed that professional soccer players felt more fatigued in the evening versus morning during Ramadan. However, among youth soccer athletes, aerobic training during Ramadan had decreased anger, confusion, depression, fatigue, tension, and TMD, and increased vigor scores regardless of whether they trained in the morning or evening (Chtourou et al., 2014).
A summary of 4 studies examining the relationship between time of day and mood in soccer players is presented in Table 6.

Limitations and recommendations for further research
This work has assessed and summarized the current literature on mood state variation in soccer players with a specific focus on training loads, training modalities, and competitive performance. However, the study was not without limitations. This review only examined studies carried out in the context of soccer and not other sports   psychological aspects of sport. Finally, we did not include relationships between POMS scores and other psychological states such as physical enjoyment or motivation. Such measures would be a valuable addition for mood assessment in soccer players. Future investigations examining mood state should be conducted with other sports disciplines (individual and team sports), include other mental health dimensions, and examine the influence of environmental condition to extend the findings of the present work.

Conclusion
This review examined relationships between training load/period, training exercises, and competitive performance on mood state in soccer players. It offers practical support for the use of a simple POMS measurement as part of an overall program to monitor the players' psychological states. Results also highlighted how those training program (e.g., training load, training modality) and competitive performance are related to mood states (i.e., tension, anger, confusion, depression, fatigue, and vigor).

Practical applications
This review was conducted to summarize the current literature on the relationships between mood state in soccer players and: (1) TL and training period; (2) training exercises (e.g., modality); and (3) competitive performance. Methods of mood regulation also emerged and were examined. POMS is a simple, non-invasive, non-fatiguing, sensitive and effective measurement tool which can help coaches monitor the psychological state of soccer players. Mood state assessment can be useful in predicting mental fatigue and quantifying emotional state of players during training. It follows that the technical staff of soccer teams should bear in mind that an increase in TL (i.e., intensity and volume of training), fatigue accumulation and poor recovery negatively affect the mood state of players.
Monitoring mood state variation during training may also help predict player performance. This strategy could be useful for coaches to determine when to implement techniques to improve stress coping and to avoid potential negative impacts of extended periods of high TL such as anxiety and loss of concentration. Better identification of athletes' psychological states allows the technical staff to select programming and strategies to achieve better outcomes during training and competition.