Furthermore, this cascade of effects has been suggested to be the possible result of body temperature changes, cytokine concentration changes, increased energy consumption/metabolic rate, central nervous system fatigue, changes in mood and anxiety symptoms, changes in heart rate and heart rate variability, changes in growth hormone secretion, changes in brain-derived neurotrophic factor secretion, improved fitness level, and changes in body composition [15]. This evidence concerns the gene BDNF and Anxiety.