Hypoxia and venous occlusion improve muscular performance but no effect on growth hormone in athletes

Abstract

Introduction: Resistance training enhances muscle strength and size; however, high-load exercise (>85% 1RM) may increase the risk of injury. Low-load resistance training with hypoxia or blood flow restriction (BFR) offers safer alternatives, although comparative data are limited. Objective: To examine the effects of hypoxia and BFR on resting growth hormone (GH) levels after five weeks of low-load resistance training. Methods: Thirty male athletes (19–24 years) were assigned to three groups: RT (50% 1RM), RT + HPX (50% 1RM under hypoxia, FiO₂ = 0.137), and RT + BFR (50% 1RM with BFR). Participants performed knee extension and flexion (3 sets × 15 reps, 1-min rest) three times weekly for five weeks. Muscle thickness, strength, resting GH, and blood lactate levels were measured before and after training. Results: After training, RT + HPX and RT + BFR showed significant increases in rectus femoris and biceps femoris thickness. Strength improved in all groups, with knee extension strength higher in the RT+HPX (30.9 ± 16.3%, p = 0.047) than RT (16.1 ± 7.3%). The resting GH levels did not differ significantly between the groups (p > 0.05). Post-exercise lactate increased significantly only in the RT+BFR (68.7 ± 57.2%, p = 0.018). Conclusion: Low-load training with hypoxia or BFR enhances muscle hypertrophy and strength, and hypoxia produces greater strength gain. Resting GH levels appear to be unrelated to these adaptations, suggesting that further studies are needed to clarify the underlying mechanisms