Introduction: Several epidemiological studies regarding endurance exercise have found that moderate exercise can benefit one's immune function, while excessive prolonged endurance trainings have the opposite effects. Post-exercise immune function depression is most pronounced when exercise is excessive, prolonged, of moderate to high intensity and performed without enough recovery time. Excessive prolonged endurance training can induce alteration in the circulating cytokines like TNF . This paper hypothesizes that exercise-related immunosuppression is due to excessive endurance trainings, producing cytokine TNF . The purpose of this study was to examine the effect of two different durations of tapering period on immune responses of TNF alteration. Methods Twenty four elite cyclists participated in a 11 week training program and were divided into two training groups. First group (age 25.25(0.78) years; weight 69.75(2.28) kg; VO2max 66.66 (0.65) ml/kg/min; means (SD)) underwent a progressive endurance exercise training program, whereas the second group (age 26.00(1.07) years; weight 67.91(2.03) kg; VO2max 66.87 (0.66) ml/kg/min) underwent an 8 week progressive endurance exercise training program (similar to first group 8 week program) followed by 3 week tapering program (50% decrease in training volume and a reduction in the training intensity to maximal 70% VO2max ). Immediately after 40 km time trail test, blood samples were taken at times corresponding to one day before the beginning of training program, after 4, 8, 9, 11 weeks training. Two groups data were compared by using ANOVA (P<0.05). Results Groups showed significant changes in endurance performance after 1 week and 3 week tapering periods 3272.83 (34.30) vs. 3203.16 (36.79) sec. after 9 weeks training and 3284.00 (32.18) vs. 3204.00 (37.62) sec. after 11 weeks training for the first and second (tapering) groups respectively (P<0.05). There were significant differences in TNF concentrations after 11 weeks training (3.94 (0.08) vs. 3.14 (0.15) pg.ml-1 for the first and second (tapering) groups respectively. Conclusions The excessive endurance exercise-induced elevations in pro-inflammatory cytokines (TNF-a) would, in turn, stimulate the release of anti-inflammatory cytokines indicating athletes are highly susceptible to infections. Our results indicate that elite endurance cyclists who reduce their training volume for 21 days can enhance endurance performance and decrease their circulating TNF concentration which indicates that there is improvement of immune function. To summarize, these results lend support to the immunosuppressive effect of excessive exercise and suggest that 3 week tapering program before major sport events is a useful method for athletes (without being detrained). These findings may have practical relevance especially for athletes forced to cut down their training intensity for some reason.
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