Swimming is an individual sport performed in an aquatic environment that is characterized by continuous and cyclic high-intensity efforts (Fortes et al., 2016; Nugent et al., 2017). Typically, an athlete competes in two to four events per competition. The official events of swimming include the following (FINA, 2016): 50-m freestyle, 100m freestyle, butterfly, breast stroke, and backstroke, 200m freestyle, butterfly, breast stroke, backstroke, and medley, 400-m freestyle and medley, and 1,500-m freestyle. It is important to note that an athlete can enter the water up to three times in the same competition (eliminatory, semifinal, and final events). Therefore, considering the short time interval (~2 h) between the swimming events in a championship (FINA, 2016), it is necessary for the athlete to start the competition with a low level of residual fatigue. In the scientific literature, heart rate variability (HRV) has been suggested as a good indicator of the stress-recovery balance state of athletes (Kiss et al., 2016; Nakamura et al., 2015; Plews et al., 2013).
HRV refers to the variation between consecutive heartbeats (Task Force, 1996), which provides information regarding the autonomic sympathetic and parasympathetic modulation of the heart. Scientific research has revealed a close relationship between HRV and sports performance (Flatt et al., 2017; Nakamura et al., 2015, Proietti et al., 2017). According to Esco, Flatt, and Nakamura (2016), athletes with improved performance show increased parasympathetic modulation and increased HRV. On the other hand, according to other researchers (D'ascenzi et al., 2014; Mateo et al., 2012; Morales et al., 2013), pre-competitive stress can lead to an increase disturbance in the autonomic nervous system, resulting in impaired HRV.
It is important to note that an increase in precompetitive stress is accompanied by increased anxiety (Fortes et al., 2016; Raglin, 1992), and there is considerable variability in the optimal pre-competitive anxiety response among athletes (Raglin, 1992). Anxiety is a multidimensional construct that refers to the willingness to respond to stress and a tendency to perceive stressful situations (Fernandes et al., 2013). Raglin (1992) emphasized that the main stressor for athletes is competition. Swimming competition, in particular, has some specific characteristics that can increase competitive anxiety. The athlete's visual contact with his opponent moments before the competition (in the control room) and the possibility of hearing the announcer pronouncing his name and that of his opponents moments before entering the water to compete may potentiate competitive anxiety.
The individual zones of optimal functioning (IZOF) model (Hanin, 2004) are widely applied to the study of anxiety related to athletic performance. According to Hanin (2004), the level of competitive anxiety necessary to achieve good performance is subjective. Fazey and Hardy (1988) proposed the Inverted-U Hypothesis, known as the Catastrophe Theory, which attempted to clarify the relationship between the different anxiety components and performance. The model proposed that cognitive anxiety acts as a splitting factor that determines whether the effects of physiological arousal are small and smooth, large and catastrophic, or somewhere in between those two extremes. The Attention Control Theory, in turn, contends that anxiety manifests in impaired attentional control, which leads to performance deficits in tasks involving the central executive function of the working memory system, causing impaired sport performance (Coombes et al., 2009). Another theory framework that has been used is the Multidimensional Theory of Competitive Anxiety (Martens et al., 1990), which subdivides competitive anxiety into three dimensions: cognitive anxiety, somatic anxiety, and self-confidence. According to this theory (Martens et al., 1990), cognitive anxiety refers to negative thoughts, expectations, and/or self-verbalizations concerning the competitive event, whereas somatic anxiety refers to the affective and physiological elements that directly affect the central nervous system. Self-confidence, in turn, is related to the level of confidence and perceived readiness to compete (Martens et al., 1990).
Blasquez et al. (2009) investigated the relationship between competitive anxiety and HRV in 10 Spanish swimming athletes, verifying increased sympathetic predominance (sympathetic tone) in athletes with a higher level of competitive anxiety. By contrast, Mullen et al. (2012) did not identify an association between competitive anxiety and HRV among electronic game athletes. Likewise, the findings of Matteo et al. (2012) did not indicate a relationship between the respective variables in cyclists. Therefore, the relevant findings from the scientific literature remain inconsistent. It should be noted that although the aforementioned studies adopted an experimental design, they lacked the premise of investigating the relationship between pre-competitive anxiety and HRV tested a few hours after a competitive event. Moreover, interestingly, those studies all used relatively small sample sizes, which preclude the generalization of the results.
Practically speaking, research that analyzes the relationship between pre-competitive anxiety levels and HRV can generate important information for sports professionals. Indeed, if a negative association between competitive anxiety and HRV is identified, the coach can plan interventions with his athletes that demonstrate a high level of competitive anxiety with the aim of attenuating it and, consequently, inhibiting the vertiginous decrease in HRV in the hours following an athletic event. Therefore, the objective of this study was to investigate the interplay of competitive anxiety and HRV in swimming athletes. We hypothesized that competitive anxiety would be negatively associated with HRV.
The present study has a quasi-experimental design involving swimming athletes of both sexes. Participants were selected in a non-probabilistic manner, and a total of 68 volunteers (41 males and 27 females) aged 15 to 16 years (15.6 [+ or -] 0.2 years) who swam the 400-m freestyle event in the Brazilian Swimming Championship Juvenile category were included. Athletes trained for an average of two h per day, often five times per week. To qualify for inclusion in the study, athletes had to fulfill the following criteria: a) be a swimming athlete for at least two years; b) systematically train in swimming for at least 8 h per week; c) be enrolled in the 400-m freestyle event of the Brazilian Championship, organized by the Brazilian Confederation of Aquatic Sports; and d) be available to answer a questionnaire and participate in anthropometric and HRV measurements. The 400-m freestyle event was...