Introduction

Physical activity and sports have long been a phenomenon of great social interest (^{García Ferrando, 1993}, ^{Sánchez Bañuelos 2002}). Sports, when correctly performed, contribute to an individual´s physical and psychological well-being, such as lower anxiety, higher concentration and less work absenteeism (^{Márquez, 2006}).

Researchers in sports psychology have been studying for many years the psychological variables related to sports practice that clearly influence in an individual´s health and performance in any context (^{Berger & Owen 1983}; ^{Márquez &Tabernero,1996}).

Regarding sports performance, researchers have generally focused on stress control (^{Moriana-Elvira & Herruzo-Cabrera, 2004}), attention (^{Hutchinson & Tenenbaum, 2007}; ^{Wulf, 2007}), self-esteem (^{Vealey & Chase, 2008}; ^{Wilson, Sullivan, Myers, & Feltz, 2004}), motivation (Amorós, 2007; ^{Bartholomew, Ntoumanis, &Thøgersen-Ntoumani, 2009}; ^{Mageau & Vallerand, 2003}) and team cohesion (^{Carron, & Eys, 2012}; ^{Spink, Wilson & Priebe, 2010}).

In recent years, coinciding with the consolidation of Positive Psychology, there has been an increased interest in analysing the importance of constructs such as psychological wellbeing (^{González, Garcés de los Fayos & García, 2012}; ^{Liberal, Escudero, Cantallops & Ponseti, 2014}), resilience (Fletcher & Sarkar, 2012; García et al. 2016; ^{Reche, Tutte & Ortín, 2014}), or optimism in sports (Fogarty, Perera, Furst &Thomas, 2016; ^{Gaudreau, Gunnell, Hoar, Thompson & Lelièvre, 2015}). The use of renown theoretical models, such as the concept of flow (^{Csikszentmihalyi, 1990}) or ^{Ryff´s Wellbeing model (1989}) in physical activity and sports, are providing interesting information that bring closer the gap between sports and health.

In this sense, one of the most relevant constructs in positive psychology is optimism (^{Marín, Ortín, Garcés de los Fayos & Tutte, 2013}). Its systemic analysis began with the re-formulation of the theory of learned helplessness in humans by ^{Abramson, Seligman and Teasdale (1978}), as a method to explain the confrontation responses to negative occurrences that appear during an individual´s life, postulating the existence of two explanatory styles: optimism and pessimism.

Together with the focus on explanatory guidelines, the other most commonly used theoretic model is the dispositional optimism developed by ^{Scheier and Carver (1987}). In this perspective, optimism is regarded as the tendency to await favourable consequences in life occurrences. This tendency can influence in the confidence and persistence to search for an objective or challenge. In this manner, the pessimistic individual is more dubious and indecisive towards many situations, being more evident in adverse conditions (Carver & Scheier, 2005).

The scientific literature correlates optimism with performance and health in various contexts. Regarding health, various studies have demonstrated its influence in disease, pain and psychological well-being (^{Chang, D’Zurilla & Maydeu, 1994}; ^{Maruta, Colligan, Malinchoc & Oxford, 2000}; McDonald & Harrison, 2016; ^{Millstein, et al. 2016}; ^{Rees, Ingledew & Hardy, 2005}; ^{Remor, Amorós & Carrobles, 2006}). Specifically, in mental health, certain researchers have positioned optimism as a protective variable against certain disorders such as depression (^{Brissette, Scheier & Carver, 2002}; ^{Extremera, Duran & Rey, 2007}; Hirsch and Lyness, 2014; ^{Sánchez & Méndez, 2007}, 2009).

Regarding performance, various studies have correlated optimism with higher confidence levels (^{Manzo, Silva & Mink, 2001}), more adequate confrontation strategies (^{Gaudreau & Blondin, 2004}), behavioural self-regulation (Gordon, 2008; ^{Norlander & Archer, 2002}; ^{Wilson, Raglin & Pritchard, 2002}),a higher control in stressful situations (^{Ortín, Garcés de los Fayos, Gosálvez, Ortega & Olmedilla, 2011}) and a higher mental robustness (^{Nicholls, Polman, Levy & Backhouse, 2008}).

Systematic reviews and meta-analysis, as methods to analyse and revise the studies of a corresponding aspect, have significantly improved the scientific quality of these studies. In this sense, ^{Gilbody and Sowden, (2000}) indicated that systematic reviews have solved the problem of the accumulating knowledge that was present in social sciences. Regarding Psychology, the traditional review articles were at risk of being biased or have contradictory conclusions. Certain authors (^{Sánchez-Meca & Botella, 2010}; Botella & Sánchez-Meca, 2015) have indicated that systematic reviews constitute a method to analyse systematically and objectively the evidence of empiric studies concerning a certain problem. Other authors, such as ^{Ferreira, Urrutia and Alonso-Coello (2011}) on the other hand, consider that reviews are second-order research, as it regards to researching that which has been researched.

In sports, there are several systematic reviews focused on training aspects such as periodization (Martín, ^{García, Salum, Sposito & Gomez, 2010}), physiological response (^{Carazo, 2013}) or its relation with cognitive and academic performance (^{Conde & Tercedor, 2015}).

Regarding health, ^{Ayala & Sainz de Baranda (2013}), analysed the quality of the studies in stretching programmes. As for sports psychology, a recent study by ^{Palmi and Solé (2016}) analysed sports interventions based on mindfulness.

The objective of the study is to discern the possible correlation between optimism and sports performance through the review of previously published studies. Also, the methodological quality of the selected scientific articles was evaluated after performing a systematic review regarding optimism and sports performance.

Materials and Methods

Search Strategy

The search was performed between January and September 2016, using the following databases: ISI Web of Knowledge, Psycinfo, SportDiscus, Scopus and Pubmed. The key words used were: athletes, sport, exercise, optimism, improve and enhancement. These key words were combined in the following manner: athletes/performance/optimism; athletes/enhancement/optimism;athletes/improves/optimism;exercise/performance/optimism/;exercise/enhancement/optimism; exercise/improves/optimism; sport/performance/optimism; sport/enhancement/optimism and sport/improves/optimism. Articles published between 1990 and 2016 were analysed. Finally, the empiric study references were revised and several prestigious experts of the field were contacted.

The systematic search process, following PRISMA guidelines (^{Urrutia & Bonfill, 2013}) resulted in a total of 630 references, allowing us to select 7 articles that complied with the inclusion criteria. A flow diagram depicting the selection process can be seen in Figure 1.

Figure 1: Flow Diagram. 

Results

The analysis of the seven selected articles was performed using two approaches. First, Tables 1 and 2 show the main data obtained from each article, emphasizing on aspects such as the theoretical model used to analyse optimism, the instrument to assess both optimism and performance, as well as a summary sentence of the correlation between the two concepts.

On the other hand, as commented in the previous section, the quality of the studies was analysed using another, more specific instrument.

As for the first analysis, it is noteworthy to comment that three of the analysed studies (Gordon, 2008; ^{Norlander & Archer, 2002}; ^{Seligman et al. 1990}) presented two different studies each, which is reflected in the tables, considering them as independent investigations.

Table 1: Analysis of the selected studies. 

Table 2: Continuation of the analysis of the selected studies.  

The analysed articles were published between 1990 and 2012. Concerning the theoretic approach to analyse optimism, three articles used explanatory methods (Gordon, 2008; ^{Martin-Krumm et al. 2003}; ^{Seligman et al. 1990}). The other studies analysed optimism using a dispositional perspective. Regarding this aspect, the works focused on disposition used the LOT and LOT-R questionnaires to assess optimism. As for the explanatory focus, the works generally used the ASQ questionnaire, except for Martin-Krumm et al. (2003)which applied a French modified version of the Sport Attributional Style Scale (^{Hanrahan, Grove & Hattie, 1989}) called Sport Explanatory Style Questionnaire (Martin-Krumm, Sarrazin, Fontayne & Famose, 2001).

Regarding the language, the majority of the studies were in English, except for ^{García-Naveira and Díaz, (2010}) and ^{Ortín et al. (2011}).

All studies, except for ^{Ortín et al. (2011}), presented data regarding reliability and/or validity of the tests used to evaluate optimism (see Table 2).

As for the method to evaluate optimism, the studies applied either the LOT or ASQ questionnaires, or modified versions of these, which are the most widely used in the literature. The Life Orientation Test (LOT) (^{Scheier & Carver, 1985}) and its reduced version (LOT-R) (Scheier, Carver & Bridges, 1994) analyse optimism from a dispositional perspective, whereas the Attributional Style Questionnaire (ASQ, ^{Peterson, Semmel, Baeyer, Abramson, Metalsky & Seligman,1982}), evaluates optimism or pessimism through the explanatory theory. The bibliometric study by ^{Marín et al. (2013}) indicated that these are the most commonly used methods to assess optimism in various contexts, including sports.

On the other hand, there is much variation in how performance was measured. Certain works used the amount of time performing a task, such as in ^{Seligman et al. (1990}) (study 1) or ^{Ortín et al. (2011}). Others, such as Seligman et al. (1990) (study 2) and ^{Norlander and Archer (2002}) measured the result of the competition. Gordon (2002) analysed the amount of success in executing a movement, such as goals, baskets, or passes. Similarly, ^{Martin-Krumm et al. (2003}) measured these same actions but in a prepared circuit. ^{De la Vega et al. (2012}) analysed the strength when using a hand dynamometer. Lastly, ^{Garcia-Naveira and Diaz (2010}) referred to the trainer´s expectations regarding the athlete´s performance, which was also measured by Seligman et al. (1990) (study 2) albeit combined with the athlete´s result in the competition.

The most relevant information from each of the 7 selected studies are explained below.

^{Seligman´s study (1990}) supposed a turning point in sports optimism research.In this study, the swimmers were given a falsely-negative feedback after the first swim. The results indicated that the more optimistic swimmers improved their time in the second swim, while the pessimistic ones significantly decreased their performance (i.e. took longer to complete the swim). ^{Ortín et al. (2011}) performed a similar study but measuring optimism through a dispositional perspective. The results of this study were similar to those observed by Seligman. In this case, although not all the optimistic athletes improved their time, those that did improve were optimistic. On the other hand, regarding the athletes that obtained worse results in the second test, the pessimistic ones obtained much lower scores than the optimistic athletes.

In 2002. Norlander and Archerpublished two studies, using swimmers and skiers, analysing their results in a competition correlating with the optimistic or pessimistic profile of the athletes, as well as their mood state during the several weeks prior to the competition. In the first study, analysing 43 skiers of different specialities, the results indicated that the athletes with higher scores in optimism obtained better results in the competition. However, the second study, using 50 swimmers, obtained contradicting results, where the optimistic athletes performed worst. Both studies were performed during national-level competitions of the respective sport.

^{Martin-Krumm et al. (2003}), used negative feedback to analyse the reaction of the individuals and the correlation between optimism, performance, anxiety and self-confidence, in 62 basketball players. In this study, the more optimistic athletes were less anxious, more confident and obtained better results in the second trial after receiving the negative feedback.

Gordon (2008) performed two studies measuring optimism and performance, while also analysing the attributional profile of the individuals. In the first work, 20 soccer players were analysed with the ASQ questionnaire and 8 competition matches were recorded, using variables such as goals, fouls committed, passes intent, passes completed, etc. In the second article, 18 basketball players completed both the ASQ and LOT questionnaires. The results of the first study indicated that the optimistic players performed better (more successful in performing their actions) after committing an error. The second study, however, obtained mixed results. The optimistic players obtained higher scores in number of assistances and interceptions, but also committed more fouls and captured less rebounds. The attributional analysis indicated that the more optimistic individuals presented an attribution in negative situations (low performance) towards the lack of effort compared to the capability.

^{García-Naveira and Díaz, (2010}), analysed the correlation between optimism and performance, as well as optimism and age. With a sample size of 151, the highest of the selected studies, the results indicated a moderately-positive correlation between optimism and performance. On the other hand, a tendency, though not quite significant, was observed when comparing optimism and age, with a higher score obtained in the older individuals.

Lastly, ^{De la Vega et al. (2012}) analysed various aspects. On one hand, the correlation between performance and self-efficacy expectations was assessed. On the other, the authors determined how a progressive increase in negative feedback could affect the individual´s performance. Lastly, the authors assessed if there were differences in performance when feedback was present or not. Using a sample of 53 soccer players, the results showed significant differences between optimism/pessimism levels regarding the self-perceived efficacy. Also, significant differences were obtained when analysing the effects of the feedback, where a lower decrease in result expectations was observed in the more optimistic individuals.

As for the analysis of the methodological quality of the studies, Table 3 depicts the values obtained in the instruments for critical reading and evaluation of the transversal epidemiological studies. The dimensions for scientific evidence were assessed in the 7 selected studies using the criteria of the instrument designed for the critical assessment of the original articles (^{Berra et al. 2008}).

Also, as indicated in the Statistical Analysis section of Materials and Methods, a Cohen´s Kappa Coefficient for qualitative values was calculated, with results ranging 0.7 to 1.

Table 3: Critical assessment of the articles and Cohen´s Kappa Coefficient.  

From the evaluation it is possible to conclude that the quality of the study was average, as the majority of the aspects assessed can be considered “good” or “average.”

The aspects with lower scores were those referring to the participants of the study, specifically their inclusion in certain experimental groups, the absence of a precise description of the inclusion/exclusion criteria used, and the methods/sources for the selection process. Also, the studies analysed should improve their sample size, as well as confidence level and statistical strength of their sample.

Discussion

The number of studies concerning optimism in sports has increased in recent years (^{Marín et al, 2013}). Optimism has been generally analysed with respect to its effect on performance. However, the number of studies that specifically measure performance is rather low, despite being the objective of the study, which is a clear methodological deficit.

Although the majority of the studies are driven based on their different theoretical foci, one of the aspects that should be more homogeneous among them is the method used to measure performance, as 6 different methods were observed among the 7 articles.

The majority of the studies regarding optimism, not only from a sports point of view, use a dispositional focus. Therefore, questionnaires LOT and LOT-R are generally used, as commented in the study published by ^{Marín et al. (2013}). One possible reason for this is that the questionnaires used in the dispositional model are much shorter than those used in the explanatory model. Regarding the dispositional model, and its correlation with the questionnaires mentioned, the scientific literature shows that there are many methods to measure or interpret the construct. As for the correction or interpretation of the questionnaires, there are two options (^{Ferrando, Chico & Tous, 2002}). On one hand, the measurement of each individual disposition can be used, whereas another possibility is to measure total optimism when the items are written in a negative manner. Certain authors consider measuring optimism and pessimism as two separate factors (^{Mroczek, Spiro, Aldwin, Ozer & Bosse, 1993}; ^{Myers & Steed, 1999}). However, ^{Cano-García et al. (2015}) compared 7 empirical models, with the final conclusion that it is more recommendable to use one sole score that represents the total level of dispositional optimism, which the authors have called vital orientation.

The studies analysed seem to indicate that there is a correlation between optimism and performance in sports. In this sense, studies such as those described here prove the importance of teaching specific strategies to the technicians and trainers in order to increase the athlete´s level of optimism.

Studies with higher quality methods are necessary to confirm this correlation between optimism and sports performance. The results of this review allow the possibility of providing various recommendations for future studies in this field. As indicated in the Results section, it is necessary to improve the methodological quality, emphasizing on certain indicators of quality (such as the method of assigning individuals into certain groups, etc) so that the results obtained may not be considered biased due to lack of proper controls. Another aspect to consider is to include a precise description of the inclusion/exclusion criteria, as well as the methods and sources of the selection. On the other hand, it is important to estimate the adequate sample size, confidence level or statistical strength of the sample. Lastly, the inclusion of statistical techniques related to meta-analysis studies should be considered in future studies.

Regarding studies relating optimism and sports, it is vital for future studies to use a single method to measure performance so that it may be possible to compare them. On the other hand, these studies should apply specific intervention programmes for a sports context in order to analyse the efficacy of possible techniques or strategies to increase optimism.

Conclusions

The objective of this study was to perform a systematic review of the scientific articles that correlate optimism with sports performance. In this sense, the number of studies is low, and even more so when the inclusion criteria included that the study must present a specific method to measure performance. Despite the low number of studies, the majority indicated that optimistic athletes performed better in competitions or when confronted to adverse situations, such as poor results (being real or informed). Only two of the studies analysed presented contradictory results, with lower performance levels detected in the optimistic athletes.

The accumulated scientific knowledge correlating performance and optimism has been rather lacking, making it difficult to obtain solid conclusions of the studies. However, it could be interesting to perform more studies of this topic since, as commented in the Introduction section. To this end, various studies have demonstrated the influence of optimism in an individual´s psychological functioning. If optimism is a method to measure health, it is possible to believe that it may improve performance, but it is very important to improve the scientific quality of the studies based on information provided in this review.