Introduction. The measurement of body composition is important for several reasons, but nowadays when obesity and overweight are common problems all over the world even more attention should be given to body composition. Excess amount of fat is itself a risk for health, but it also predisposes to many diseases, one of which is diabetes. It has been shown that with regular physical activity and exercise the body composition and body’s glucose regulation can be improved. In common activity guidelines the amount of traditional endurance and resistance training takes hours per week to perform to fill the recommendations. However, since it has been shown that one of the most common reasons for not participating in exercise is lack of time, therefore highintensity interval training (HIIT) might be one option. HIIT takes less time to perform, since it consists of short, high-intensity work periods separated often by even shorter, lower intensity recovery periods. Altogether one HIIT session takes in average 30 minutes. In studies it has been shown that with HIIT type of training similar and even greater improvements have been gained in different study populations regarding body composition and glucose tolerance as with traditional endurance and resistance training. Therefore, the purpose of this study was to investigate and compare the effects of eight weeks of high-intensity interval running (HIRT), high-intensity interval circuit training (HICT) and steady-state endurance running (SSE) on body composition and glucose tolerance.

Methods. Subjects were recreationally active adults, with normal glucose tolerance, weight and body mass index (BMI). After medical evaluation and electrocardiograph (ECG) test they were randomly divided into three training groups. All subjects participated in pre and post measurements, which included body composition measurement with dual-energy x-ray absorptiometry (DXA), oral glucose tolerance test (OGTT), and for another thesis maximal oxygen consumption (VO2max) test (with cycle ergometer) and measurement of excess post exercise oxygen consumption (EPOC). In between they performed three exercise sessions every week for eight weeks. The training consisted of 8–10 x 1 min submaximal running intervals separated with 30 s active recovery for HIRT, 8–10 exercises performed maximally as circuit training (one minute per exercise) separated with 30 s recovery between the movements for HICT and for SSE 40–60 minutes steady state running. In addition, the subjects filled out a food diary twice during the study period and the diaries were analyzed with NUTRI-FLOW program.

Results. After the training period, the SSE group had a statistically significant decrease in weight (63.21 ± 5.51 vs. 62.49 ± 5.24 kg, p = 0.043) and BMI (22.63 ± 1.31 vs. 22.19 ± 1.21, p = 0.028). In DXA results, the only significant findings were a decrease in the fat-free percent of the SSE group (77.80 ± 9.93 vs.74.40 ± 9.82 kg, p = 0.028) and a decrease in fat mass of the arms in the HICT group (1.51 ± 0.88 vs. 1.47 ± 0.87 kg, p = 0.046). In OGTT the only significant findings were decreases in the HICT group in blood insulin concentration at 60 minute time point (400.29 ± 134.24 vs. 347.28 ± 133.69 mmol/l), p = 0.046) and in fasting insulin in the combined high-intensity interval training group (HIRT & HICT) (76.17 ± 26.73 vs. 51.20 ± 17.56 mmol/l, p = 0.034). There were no significant changes in the food diary results.

Discussion and conclusions. Based on the result it seemed that SSE was the most effecting training mode to gain decrease in weight. However, the subjects had a tendency to lose both, fat and fat-free mass, and the decrease in fat-free percent was significant, and no significant changes were observed in HIRT or HICT. This indicates that with more intense training the subjects in the HIIT groups were able to maintain their fat-free mass better. It also seemed that the HICT program was especially loading for the arms, since the fat mass decrease in arms was significant. In previous literature, it has been noted that site specific fat loss would not happen along with training, but the result of the HICT group in this study indicates the opposite. This aspect needs to be studied more in the future. The results of OGTT suggest that the high-intensity interval training was more effective regarding glucose tolerance. Only few statistically significant findings were made in this study and no significant differences between the groups were found. However, that can be seen as a positive result, since the benefit of moderate intensity, steady-state exercise is well recognized in previous literature, and the high-intensity interval training groups did not differ from SSE.