The influence of competitive exercise on aggression, testosterone, cortisol, and cardiac vagal activity

Objectives. Exercise is often used as an intervention to reduce aggressive behaviour. However, despite this widespread use, it is unclear under what conditions exercise can actually reduce aggressive behaviour (Pels & Kleinert, 2016). Competition is thought to increase aggression because it increases frustration (Breuer & Elson, 2017). This study aims to investigate the acute effect of competition on aggression during exercise. We expected exercise without competition to lead to less aggression than a competition-oriented exercise task, and, in accordance with the dual-hormone hypothesis (Mehta & Josephs, 2010), to lower testosterone and higher cortisol. Furthermore, cardiac vagal activity is expected to be higher in the individual condition compared to the competition condition.
Methods. 73 male students took part in the study. After an aggression induction, participants exercised on a bicycle ergometer at a moderate intensity in two conditions: They cycled either alone or against a fictitious opponent. Subsequently, the hot-sauce paradigm (Lieberman et al., 1999) was used to measure aggressive behavior, in which participants were asked to give to the fictitious opponent any amount of hot sauce. At 5 different time points, testosterone and cortisol were measured via saliva sample and cardiac vagal activity was measured via electrocardiogram.
Results. The competition group showed more aggressive behaviour after exercise than the individual group (t(71) = 2.123, p = .037, d = 0.498). However, this difference could not be shown on a physiological level.
Conclusion. The study shows that exercise without a competitive stimulus can lead to less aggressive behaviour compared to exercise with a competitive stimulus, although this effect may not be strong enough to cause differences at the physiological level. The lack of correspondent physiological reaction might be due to the low intensity of aggression induction. Future studies should replicate the present study using a stronger aggression induction.