The relationship between stress and athletic performance is of interest to both researchers and athletes. For the last 25 years the inverted-U theory of arousal and performance has dominated thinking within the field of sport psychology. This hypothesis described the relationship between physiological arousal and performance as forming a curvilinear function in the shape of an inverted-U. Hanin's Zones of Optimal Functioning (ZOF) theory, more recently referred to as the Individual Zones of Optimal Functioning model, posits that each athlete has an optimal range of state anxiety where he or she performs best. Unlike the inverted-U hypothesis, however, this optimal level of state anxiety is a bandwidth that may be low, medium or high. Also, over the past decade it became clear that stress is a process and consists of many components like psychological, biological, physical and behavior responses. The focus in this study was on biological cortisol measures and applicating the ZOF model.