Introduction
Athletes are often required to perform complex sporting skills in challenging and social evaluative environments. The subjective evaluation and appraisal of the athlete’s ability to cope with the stressors of competition influence the development of negative emotional states.1 These negative emotions (eg, anxiety) are expected to trigger a biological stress response through activation of the sympathetic nervous system (SNS) and the hypothalamic-pituitary-adrenal (HPA) axis with the hormone cortisol as a marker of HPA-axis activation.2 However, both pathways are activated by distinctive psychological determinants.3 Challenge and effort are linked to SNS activation, whereas lack of control, harm and unpredictability outcome are more associated with HPA-axis activation.3–5 Due to the high level of agreement between serum and salivary cortisol concentrations and the ease of collection, studies more regularly use salivary cortisol as an indicator of HPA-axis activation over serum analysis.6 Based on the systematic analysis of laboratory studies of acute psychological stressors, Dickerson and Kemeny4 identified that cortisol is released under motivated, goal-relevant performance tasks during social-evaluative conditions. As these psychosocial factors resemble the psychological stressors of competitive sport, it is of interest to systematically examine whether participation in sport competition activates the HPA-axis. Craft et al 7 identified via a meta-analysis the presence of an emotional response (eg, cognitive and somatic anxiety) to anticipating sport competition. In addition, Hayes et al 8 systematically examined the physiological effects of sport competition on the cortisol response and concluded that an increase in cortisol after sport competition was influenced by the timing of precompetition sampling and in particular the suggested presence of an anticipatory stress response.
A strong anticipatory rise in cortisol has been identified in anticipating participation in extreme sports9 10 as well as in social-evaluative laboratory stressors.4 An anticipatory increase in cortisol before sport competition is important to prepare for the psychological and physiological demands and is suggested to affect sport performance through its influence on cognitive processes (eg, prefrontal cortex-amygdala activation and deactivation11 12). There is evidence that a moderate increase in cortisol is associated with reduced reaction time to identify task relevant stimuli and increased inhibition of aversive stimuli (eg, pictures of fearful faces or violent scenes) in comparison to low and high levels of cortisol secretion, which could facilitate sport performance.13 In contrast, high levels of cortisol are associated with a reduction in inhibition of task irrelevant stimuli, suggesting a debilitative effect on sport competition.14 Thus, moderate levels of cortisol might positively influence performance compared with low and high levels supporting the presence of an inverted U-relationship between cortisol and performance.
Variety in HPA-axis activation and cortisol reactivity is influenced by factors such as genetic predisposition as well as determinants such as gender, age and habituation.2 15 Kirschbaum et al 16 identified that males demonstrated increased levels of salivary cortisol concentration in anticipation of participating in a social stress task, but this anticipatory stress response was absent in females. In contrast, van Stegeren et al 17 did not identify gender differences in cortisol response. It is relevant to note that the gender differences in HPA-axis activity to social stress tasks are still unclear due to confounding effects of factors such as age, contraceptive use and predominantly due to differences in the appraisal of psychosocial stressors used in stress protocols.18 Gender differences in HPA-axis activity have also been the primary aim of studies in the sport domain. Kivlighan et al 19 identified no gender differences in cortisol concentration in the anticipation phase of competition. Salvador20 concluded that the anticipatory cortisol response to sport competition is often absent in women. Therefore, an investigation into HPA-axis activity in anticipation to sport competition should consider the moderation effects of gender.
Where the effects of gender differences on HPA-activation is inconclusive, an even more complex interaction takes place with the effects of age, experience and habituation to stressful events. Experienced athletes have had more exposure to stressful competition. It is suggested that repeated exposure to stressful events reduces the HPA-axis activation in social stress tasks21 as well as in extreme sports (eg, sky-diving).22 However, the peak cortisol concentration before sky-diving is not different between experienced versus less experienced sky-divers9 where the pattern of cortisol reactivity (eg, quick rise and reduction) is distinct.10 Therefore, it is anticipated that age and experience might play a greater role in the pattern of cortisol reactivity than in the magnitude of the cortisol response.
One of the key challenges in investigating the psychosocial effects of sport competition on the cortisol response is separating cortisol secretion due to emotional stress or due to physiological demands of the exercise. Exercise intensity influences blood glucose levels and declining blood glucose levels elicit the hypothalamus to secrete the corticotrophin releasing hormone (CRH). CRH triggers the release of the adrenocorticotropic hormone which activates the adrenal cortex to release cortisol.23 The release of cortisol in this mechanism supports homeostasis of blood glucose levels by stimulating gluconeogenesis from amino acids and mobilising free fatty acids from adipose tissue.23 Cortisol secretion with the aim of mobilising energy sources is therefore independent from experiencing psychosocial stressors and is mainly a function of exercise intensity. Indeed, Jacks et al 24 identified that blood glucose significantly decreased while salivary cortisol significantly increased after 59 min of high intensity exercise in comparison to rest and low-intensity exercise. This finding is supported by the conclusion from Kudielka et al 15 that both maximal physical exercise and sustained exercise above 70% of the VO2max will significantly increase cortisol concentrations compared with moderate exercise intensities. Therefore, to examine psychosocial stress and cortisol reactivity in sport competition, it is important to investigate the anticipatory stress response in contrast to exercise induced changes. If precompetition cortisol has a possible influence on sport performance, it is of interest to examine the magnitude of this anticipatory cortisol response. By means of a meta-analysis, it is possible to aggregate the results of other studies and to examine the influence of moderating variables on the anticipatory cortisol response before competition.