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Background and Aim: Low-volume, high-intensity interval training (HIT) increase skeletal muscle aerobic capacity, yet little is known about the potential mechanisms in improvement of this adaptability. The purpose of present study was to examine the effect of four weeks of HIT on peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) and vascular endothelial growth factor (VEGF) protein contents in skeletal muscle of active men. Materials and Methods: Eight active male students voluntarily and purposefully participated in this study. One week before the experiment started; subjects were familiar with protocol of research. Needle biopsy samples vastus lateralis were obtained 48 h before training and 72 h after the final training session. HIT protocol consisted of 11-15 bouts of 1 min cycling at ∼85-90% of reserve heart rate separated by 1 min of active recovery between each, 3 sessions per week for 4 weeks. Variables were measured by ELISA. All data were analyzed using paired t-test and at the level of significance of p ≤ 0.05. Findings: Results of study showed the four weeks of HIT lead to significant increase in PGC-1α and VEGF (p < 0.001). Conclusion: Our findings suggest that activation of VEGF from PGC-1α pathway is part of cellular-molecular mechanisms of high-intensity interval training. So, probably angiogenesis in skeletal muscle is one of the most important factors in improving of aerobic performance, which requires more studies.

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Background and Aim: Obesity is a clinical condition that affects the growth-related hormonal system, especially in adolescents. High-Intensity Intermittent Training (HIIT) might reduce such destructive effects.
Methods & Materials: In this quasi-experimental research, among adolescent boys [age: 13-18 years, height: 154±8 cm, Body Mass Index (BMI): 27.05±1.4 kg/m²], 30 volunteer subjects were selected. The study participants were divided into 3 groups of short-term and long-term periodic exercises as well as controls. The short-term exercise group performed 9 bouts of 30 seconds with 150-second breaks between sessions; the long-term exercise group performed 4 bouts of 150 seconds with 240-second breaks between sessions 3 times a week for 8 weeks. Body composition and blood samples were obtained 48 hours before and after conducting the training protocol to measure the desired parameters. The changes of each index were analyzed by repeated-measures Analysis of Variance (ANOVA)  at the significant level of P<0.05.
Ethical Considerations: This study was approved by the Ethics Committee of Tabriz University (Code:  IR.TABRIZU.REC.1398.021).
Results: After 8 weeks of HIIT, growth hormone increased and thigh, arm circumference, and fat percentages decreased (P<0.05). However, no changes were detected in the insulin-like growth factor I, BMI, and weight of the examined subjects (P>0.05).
Conclusion: Short- and long-term HIIT have the potential to improve the growth hormone status and body composition of overweight adolescents.