The purpose of this study was to examine the effect of incremental continuous running as well as morning vs evening-time training on changes in serum immunoglobulins including IgA, IgG, IgM, testosterone and cortisol hormones responses. For this reason, 28 male athletic students were purposefully selected and randomly divided into the two groups; morning-time training group (N = 14, weight 68.2±9.8 kg, age 19.5± 1.6 years, training time 7: 30 AM) and evening-time training group (N=14, weight 63.8±8.4 kg, age 19.81±1.24 years, training time 16:30 PM). The participants were trained according to an incremental continuous running program with a certain heart rate for two months (16 sessions). To determine the amount of serum immunoglobulins as well as cortisol and testosterone hormones, the participants’ blood samples was taken twice, once 24 h before the first training session and once 24 h after training session. Then, a 12-minute running-walking test was used to measure the maximal oxygen consumption. The results showed there were not any significant differences between the amounts of IgA, IgM, IgG serum of both groups in pre-test and post-test (i.e., respectively, p = 0.727, P = 0.068, P=0.14). Also, there were not any significant differences between the amounts of testosterone and cortisol hormones secreted of both groups in pre-test and post-test. However, there were significant differences between the concentrations of cortisol hormone of the two groups in pre-test (P = 0.006) and post-test (P = 0.0001). More ever, the results also showed a significant difference between the pre-test of the morning-time training group and the post-test of the evening-time training group (P = 0.0001). The findings of this research indicate that cortisol hormone is influenced by the time of training, which is due to circadian rhythm.
