Introduction: Insulin resistance is one of the biggest medical problems in overweight population. So, the purpose of the present study is to determine the effectiveness of a four-week concurrent training with and without caffeine ingestion on the levels of insulin resistance indices of the overweight girls.
Methods: For this purpose, 20 overweight female students resident in dormitories of Tabriz university (mean body fat 33.43±1.91% and BMI 28.21±2.05 kg.m²) were chosen. After completing consent forms in  a randomized double-blind clinical trial, they were divided into two homogeneous groups of 10 subjects; Caffeine and  Placebo (each one 5 mg.kg^-1.day) along with a 4-week concurrent aerobic-strength training (30 min of aerobic activity with intensity between 65-85% HRreserve and 30 min of resistance exercise with the intensity of 70-75% 1-RM; 3 days per week). Blood samples were taken at two phases (baseline and 24-hours after supplementation and exercise training period). Data were analyzed using dependent t-test at level α≤0.05.
Results: The results showed that the fasting serum blood glucose (62.98 vs 67.51 mg.dl) and insulin levels (14.27 vs 16.15 µm.ml) and insulin resistance index were significantly decreased in two groups (P=0.03) after the 4-week supplementation. Whereas, this reduction in caffeine group was not statistically significant (P>0.05) compared with placebo group.
Conclusion: It seems that four weeks of compound training of aerobic and resistance training alone and also in interaction with caffeine supplementation is effective on relative improvements of this indices.