Growth hormone regulation in two types of aerobic exercise of equal oxygen uptake

Summary

Five normal men, aged 23 to 35 years, participated in two bouts of continuous aerobic cycling separated by five days. The first type of exercise (EI) was cycling at a pedalling frequency of 50 rev · min⁻¹ with a load which produced a steady state O₂ uptake of approximately 40% of the subjects'$\dot V_{O_{_2 max} }$. The second type of exercise (EII) was cycling at a pedalling frequency of 90 rev · min⁻¹ with a load such that an equal steady state$\dot V_{O_2 }$ was reached and maintained. Both EI and EII lasted 40 min. GH levels increased in EI and EII, reaching their maximum at 8 min of recovery (245 and 300% of resting values, respectively).

No significant differences were observed between EI and EII in GH, lactate, glucagon, insulin, cortisol and glucose levels between the two exercises. While it has been reported earlier that GH levels were frequently related to lactate levels and/or decreased O₂ availability (Sutton 1977; Raynaud et al. 1981; Kozlowski et al. 1983; VanHelder et al. 1984a, b), this study suggests that the opposite is also valid, that is, different types of exercise of equal$\dot V_{O_2 }$, duration and lactate production do not produce significantly different GH responses.