HYPOXIA DOES NOT STIMULATE HORMONAL CHANGES TO PROMOTE MUSCLE HYPERTROPHY
Kurobe, K., Huang, Z., Ozawa, G., Tamaki, H., & Ogita, F. (2009). IGF-I and hormonal responses to arm-curl exercises under different hypoxic conditions. A paper presented at the 14th Annual Congress of the European College of Sport Science, Oslo, Norway, June 24-27.
This study examined the effects of arm-curl exercising under different hypoxic conditions on insulin-like growth factor-I (IGF-I) and hormonal responses, both of which relate to muscle hypertrophy. Healthy males (N = 8) performed an exhaustive arm-curl exercise in three different conditions; 1) normal condition, 2) hypoxic condition corresponding to an altitude of 3,000 m, and 3) to 5,000 m above sea-level. Arm-curl exercising was loaded at a pre-determined 8 RM and performed to exhaustion in each set, and repeated three times with one-minute rest between sets. The range of elbow joint motion was from 10 to 100° (0°at full extension), and the exercise was performed at a fixed cadence (flexion action three seconds, extension action three seconds). Before the exercise, S rested in a sitting position for 30 minutes breathing the gas of each condition. Blood samples were obtained before, and immediately, 15 minutes, and 30 minutes after the exercise to determine serum IGF-I, growth hormone, cortisol, and blood lactate concentrations.
Mean values of blood lactate immediately after the exercise were significantly higher than those before the exercise in all conditions. Blood lactate levels at the highest simulated altitude remained significantly higher until 15 minutes after the exercise when compared to before the exercise. When the time-courses of serum growth hormone were compared between conditions, no significant changes were observed. However, when blood lactates were compared among conditions, the values at 15 and 30 minutes after the exercise were significantly higher in the highest altitude simulation than in the other conditions. The time-course of serum cortisol did not change significantly in all conditions. In the comparison among conditions, serum cortisol at 15 and 30 minutes after the exercise were significantly higher in mid-altitude condition compared to the normal condition. For serum IGF-I, neither time-course of changes in each condition nor differences among conditions were found.
Implication. Hypoxic stimuli can enhance hormonal responses that relate to muscle hypertrophy but a mild hypoxic stimulus corresponding to 3,000 m above sea-level would not be strong enough to induce muscular development. Serum IGF-I does not change within 30 minutes after strenuous exercise in hypoxic conditions.
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