The acute stress response to two different laboratory stress tests in physically active individuals – A pilot study

Introduction The response to stress is driven by two interdependent systems: the hypothalamic-pituitary-adrenal (HPA) axis and the autonomic nervous system (ANS), which regulate cardiac control, endocrine levels, and immune function (Tsigos et al., 2000). Previous research suggests that regular exercisers show reduced responses to acute psychosocial stressors (Mücke et al., 2018). Nevertheless, it is currently unknown if the stress response in exercisers depends on the type of stressor and physiological marker of interest. Also, little research has directly compared male and female participants. Understanding the specificity of the response is crucial for designing future research on exercise and stress. This pilot study should clarify the feasibility of the presented design and methods to address this research gap. Methods We adopted a crossover design, exposing subjects to two laboratory-based stress tests in random, counterbalanced order. The Trier Social Stress Test (TSST; Kirschbaum et al., 1993) induces psychosocial stress, while the Maastricht Acute Stress Test (MAST; Smeets et al., 2012) incorporates additional physiological components by immersing one hand in ice water. Young, healthy, physically active subjects (n = 12; 6 females, 6 males; age = 20-3 yrs) were invited to the laboratory twice, one month apart. Females were eumenorrheic and invited within the self-reported mid-luteal phase. Participants were asked to arrive well-rested and under standardized dietary conditions. After a 15-minute resting period during which baseline measures were taken, participants underwent the stress test. Subsequently, participants sat in a quiet room for follow-up sampling of heart rate (HR), serum blood (+0 min, +5 min, +25 min), saliva, and subjective stress via a 100 mm visual analog scale (VAS100; +0 min, +5 min, +10 min, +15 min, +25 min). Free cortisol and HR were defined as primary markers for HPA and ANS activity, respectively, and analyzed using a timepoint x test x sex ANOVA followed by the Games-Howell. VAS100 was analyzed using continuous ordinal regression. Results HR was higher during the TSST than the MAST (∆ HR = 21.1 bpm, 95% CI 8.8, 33.4). No sex differences for HR were found. Sex differences indicate lower cortisol in females (g = 0.87, 95% CI 0.49, 1.26), but no time- or interaction effects were found (p > 0.05). VAS100 significantly increased following the stress tests. The MAST evoked higher VAS100 than the TSST (g = 0.46, 95% CI 0.13, 0.79), and women reported higher levels of subjective stress than men (g = 0.62, 95% CI 0.29, 0.95). Discussion While HR is a marker of ANS activity, the amount of movement during the interview phase might increase HR during the TSST. On the other hand, the VAS100 might reflect the physical pain experienced by the ice water and less so the psychosocial component. Despite increases in subjective stress, cortisol levels exhibited no change. This difference is in line with previous work hypothesizing even a protective effect of cortisol on subjective stress (Het et al., 2012). We conclude that the design is promising for testing hypotheses concerning the physiological and subjective stress response during acute laboratory stress tests in an exercising population. As this is a pilot study, inferential statistics should be read cautiously. This study was designed to facilitate a larger-scale project with sufficient power. References Het, S., Schoofs, D., Rohleder, N., & Wolf, O. T. (2012). Stress-induced cortisol level elevations are associated with reduced negative affect after stress: Indications for a mood-buffering cortisol effect. Psychosomatic Medicine, 74(1), 23–32. https://doi.org/10.1097/PSY.0b013e31823a4a25 Kirschbaum, C., Pirke, K. M., & Hellhammer, D. H. (1993). 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