Smile Intensity in Volleyball Players' Pro le Photographs is Unrelated To Sports Performance


 Studies indicated that individuals who tend to smile while taking their photographs tend to experience more positive emotions in their life and, in turn, achieve superior outcomes in several life domains. However, little is known whether positive emotionality revealed in players' profile photographs is related to sports performance. This study examined whether the smiling intensity in volleyball players' profiles (full, partial, and no smile) predicted individual (e.g., points scored, service, and reception errors) and team performance (winning a match). Building upon previous studies on positive emotions, we expected that players presenting full (Duchenne) smiles would achieve better results. We analyzed 196 volleyball players' profiles from the Polish highest-level professional league competition (PlusLiga). Raters coded smile intensity. Using three-level path models, we found that teams with more frequent Duchenne smiles performed as well as those who presented Duchenne smiles less often. We conclude that positive emotionality (as reflected in profile photo smiling) might be independent of male volleyball accomplishments.


Introduction
Positive emotions, and their expression, broaden people's mindsets, build lasting physical, psychological, social, and intellectual resources, and support optimal functioning [1]. In sports, positive emotions facilitate the performance in softball [2], basketball [3], sprint races [4], cross-country skiing [5], and esport [6]. Studying emotions in top-level athletes is challenging due to restricted access. One approach that overcomes limited access is the thin-slicing method, which uses segments of expressive behavior (e.g., smiles in publicly available photos) to predict meaningful life outcomes [7] [8] [9]. Of particular interest in the domain of emotions and performance is Duchenne smiling -a valid marker of positive emotionality signaling underlying positive emotions and positive affective traits such as interpersonal warmth [1] [10]. This type of smiling is characterized by muscle contraction around the mouth and the eyes. Duchenne smiles differ from fake or forced smiles that re ect intentions rather than experience or asymmetrical smiles that re ect contempt rather than positive emotions.
Research showed that individuals smiling in pro le photos more intensely live longer [7], have higher life and marital satisfaction [11] [12] [13], are more competent [11], and achieve greater professional success [14]. Individuals who tend to smile in photos are also more caring for others, sociable, and interpersonally warm [11], factors that might be relevant to team sports performance. In sports, the research on smiling is limited. However, a recent experimental study indicated that smiling predicts running performance [15].
Nevertheless, no study to date tested whether pro le photo smiling was predictive of sports success.
Considering the support for the facilitating role of positive emotions in sports, we aimed to investigate whether pro le smiling data would su ce to predict athletes' performance. Building upon prior studies, we expected teams and individuals to perform better: 1) teams whose players express Duchenne smile more often to win more matches, and 2) players expressing Duchenne smile to achieve better results.

Stimuli
We used publicly available photos (N = 196) presenting Polish highest-level volleyball league (PlusLiga) male volleyball players in the 2019/2020 season from all 14 PlusLiga teams. As for the player specialization, data involved 57 outside hitters, 54 middle blockers, 29 opposite hitters, 28 setters, and 28 liberos. Players' age ranged from 19 to 41 years (M = 28.38, SD = 4.74). Players played from 1 to 25 matches in the season, resulting in 3596 cases of performance to analyze. A power analysis using G*Power 3.1 [16] indicated that 543 cases would allow detecting small effect sizes of f 2 = 0.02, with the power of 0.95, for the regression coe cient.

Smile Intensity
Ten raters blind to the research questions evaluated players' pro le pictures. Raters coded smiles using three categories -Duchenne smile (full smile), partial smile or asymmetrical smile, and no smile [14] [17]. A Duchenne smile is a facial expression characterized by the contraction of muscles around the mouth and the eyes that is closely related to the pleasant experience. A partial smile is a facial expression characterized by contraction of muscles only around the mouth, e.g., zygomaticus major, which draws the angle of the mouth upward. An asymmetrical smile is a facial expression characterized by the contraction of muscles around one side of the mouth, which draws the angle upward. Raters determined whether players presented no smile (coded as 0) vs. partial smile or asymmetrical smile (coded as 1) or Duchenne smile (coded as 2). The dominant rating for the raters was used as the smile intensity score for each photo. The interrater agreement was satisfactory (Krippendorff's α = 0.73) [18].

Sports Performance
We used publicly available statistics from the PlusLiga website (www.plusliga.pl) to measure volleyball performance. We collected data across one season on the number of 1) sets and matches played by each player, 2) scored points, spike errors, perfect reception, reception errors, points scored blocking, service aces and service errors, and 3) match results (binary coded as defeat = 0, win = 1). We used the match results as a team performance indicator, and the scores, spike errors, perfect reception number, reception errors, points scored blocking, service aces, and service errors as the player performance indicators.

Statistical strategy
We tested whether smile intensity predicted volleyball performance using multivariate regression models in Mplus 8.5 [19] [20] [21]. We run ve three-level models to account for within-player (level 2) and within-team (level 3) data dependency. The multivariate regression model regressed outcome variables speci c for players' role (position) on dummy coded smiling intensity (no smile category as the reference category), controlling for age. For instance, we regressed scoring points performance (scored points, spike errors, and spiking number) on smile intensity among players whose primary role was in scoring points, i.e., opposite hitter, outside hitter, middle blocker/hitter controlling for the sum of spikes. We regressed reception performance (reception errors, number of perfect reception) on smile intensity among players who receive served balls, i.e., libero and outside hitter controlling for the sum of receptions. We regressed blocking performance (points scored blocking) on smile intensity among players whose primary role is scoring points, i.e., all players except libero. We regressed service performance (service aces and service errors) on smile intensity among players who serve the ball, i.e., all players except libero controlling for the sum of services. Furthermore, we ran the logistic regression model, regressing the match results (defeat vs. win) on the smiling intensity. We used the Bayesian correction estimator [20]. Signi cant coe cients are indicated by 95% con dence intervals that do not include zero. Data and scripts are available in supplementary materials.

Results
Descriptive statistics Table 1 presents means, standard deviations, and the correlation matrix.

Blocking Performance
Players that expressed Duchenne smile had the same number of points scored blocking, β = -.10, 95% CI [-.28, .07], compared to players that did not smile. Players who smiled partially or asymmetrically had the same number of points scored blocking, β = -.07, 95% CI [-. 25

Discussion
We examined smile intensity revealed in volleyball players' pro le pictures as a marker of positive emotionality and related it to players' performance. We found that positive emotionality revealed in pro le pictures was unrelated to the individual or team performance. These ndings are the rst to suggest that positive emotionality estimated from pro le pictures does not predict volleyball performance. This adds to cumulative and complex evidence of how and to which extent emotions and their expression are related to sports outcomes. Players performed equally well whether they smiled or not. These ndings add to the complexity of previous studies showing that smiling can hamper [22] or facilitate [15] sports performance. Our nding is a caveat because elicited positive emotions usually improve sports performance across many contexts [2] [3] [4] [5] [6]. However, our ndings suggest that a happier facial expression revealed in a pro le picture of volleyball players does not convey meaningful information that might predict sports outcomes.
We also found that team members' positive emotionality determined by the smiling expression did not in uence the team's odds of winning or losing. Again, previous studies pointed out team-related positive emotionality as a predictor of successful team sports performance [23]. Thus, our ndings reveal that accounting for smiling expressions disclosed on players' photos might be insu cient to understand team emotionality and predict their outcomes. Our ndings add another perspective to the stream of research on smiles, emotions, and sports performance.

Limitations and Future Directions
The study had several limitations. First, we investigated photos exclusive to the PlusLiga players. Therefore, the results cannot be generalized to the whole discipline. Future studies might validate our ndings with photos from different leagues (covering a variety of countries and cultures) focusing on the broader range of facial expressions.
Second, the strength of the relationship between smiles and performance outcomes depends on the study material. For instance, it is more signi cant when smiles are captured in lms than in photos [24]. More accurate estimation of positive emotionality, e.g., video material, might provide different results [17] [25]. Future research might use publicly available brief video clips of speci c game actions to assess the smile category in the wild. Furthermore, we cannot rule out the possibility that some players were instructed to pose in a speci c way to present the photographer's artistic intention. Future studies might use players' photos from other sources (e.g., social media) that might be more representative of players' daily emotionality.
Third, the study is cross-sectional, and causality cannot be determined. For instance, we cannot distinguish whether achievements preceded or followed happier expressions. Research suggests that bidirectional in uences are likely, i.e., achievements lead to happiness and happiness lead to achievements [26]. Future longitudinal studies might link photos taken before each match or action to establish to which extent the smile predicts or follows particular match results or both. Smiling might be more predictive of sports performance for photos taken close to the competition [22].
Finally, although the validity and accuracy of the thin-slicing methodology using pro le photo smiles have been evidenced [7] [11] [14], inferring emotions based on facial movements is considered risky [27].
For decades, Duchenne smile was considered a genuine positive emotions indicator [1]. However, the latest studies undermine these ndings [25] [27]. Our ndings might favor these new theoretical approaches. The correspondence between facial movements and experiencing distinct emotions is often not straightforward [27]. Facial con gurations are not " ngerprints" of emotional states regardless of individual, social and cultural context [27].

Conclusions
Our ndings indicated that positive emotionality, determined via pro le photos smiling analysis, is not related to volleyball performance. A major strength of this study is that we used publicly available objective data and documented how smiles manifest in players' o cial pro le pictures and how this thin slice of expressive behavior is related to sports performance. A further examination of players' emotionality, e.g., emotions experienced across daily training or competitive contexts, might be necessary to learn more about the role of positive emotionality in volleyball.