title: Hormonal and metabolic responses to repeated cycling sprints under different hypoxic conditions.
abstract: OBJECTIVE
  Sprint exercise and hypoxic stimulus during exercise are potent factors affecting hormonal and metabolic responses. However, the effects of different hypoxic levels on hormonal and metabolic responses during sprint exercise are not known. Here, we examined the effect of different hypoxic conditions on hormonal and metabolic responses during sprint exercise.
  
  
  METHODS
  Seven male subjects participated in three experimental trials: 1) sprint exercise under normoxia (NSE); 2) sprint exercise under moderate normobaric hypoxia (16.4% oxygen) (HSE 16.4); and 3) sprint exercise under severe normobaric hypoxia (13.6% oxygen) (HSE 13.6). The sprint exercise consisted of four 30s all-out cycling bouts with 4-min rest between bouts. Glucose, free fatty acids (FFA), blood lactate, growth hormone (GH), epinephrine (E), norepinephrine (NE), and insulin concentrations in the HSE trials were measured before exposure to hypoxia (pre 1), 15 min after exposure to hypoxia (pre 2), and at 0, 15, 30, 60, 120, and 180 min after the exercise performed in hypoxia. The blood samples in the NSE trial were obtained in normoxia at the same time points as the HSE trials.
  
  
  RESULTS
  Circulating levels of glucose, FFA, lactate, GH, E, NE, and insulin significantly increased after all three exercise trials (P < 0.05). The area under the curve (AUC) for GH was significantly higher in the HSE 13.6 trial than in the NSE and HSE 16.4 trials (P < 0.05). A maximal increase in FFA concentration was observed at 180 min after exercise and was not different between trials.
  
  
  CONCLUSIONS
  These findings suggest that severe hypoxia may be an important factor for the enhancement of GH response to all-out sprint exercise.
authors.affiliation: School of International Liberal Studies, Chukyo University, 101-2 Yagotohonmachi, Showa-ku, Nagoya 466-8666, Japan; Department of Sports Sciences, Japan Institute of Sports Sciences, 3-15-1 Nishigaoka, Kita-ku, Tokyo 115-0056, Japan. Electronic address: kon.michihiro@gmail.com.
authors.forename: Michihiro
authors.initials: M
authors.lastname: Kon
authors.affiliation: Department of Sports Sciences, Japan Institute of Sports Sciences, 3-15-1 Nishigaoka, Kita-ku, Tokyo 115-0056, Japan.
authors.forename: Kohei
authors.initials: K
authors.lastname: Nakagaki
authors.affiliation: Department of Sports Sciences, Japan Institute of Sports Sciences, 3-15-1 Nishigaoka, Kita-ku, Tokyo 115-0056, Japan.
authors.forename: Yoshiko
authors.initials: Y
authors.lastname: Ebi
authors.affiliation: Department of Physical Education, Nippon Sport Science University, 7-1-1 Fukasawa, Setagaya-ku, Tokyo 158-8508, Japan.
authors.forename: Tetsunari
authors.initials: T
authors.lastname: Nishiyama
authors.affiliation: Centre for Physical Activity and Nutrition Research, School of Exercise and Nutrition Sciences, Deakin University, 221 Burwood Hwy, 3125, Australia.
authors.forename: Aaron P
authors.initials: AP
authors.lastname: Russell
mesh_terms: D000328:Adult; D015444:Exercise / Q000502:physiology*; D005230:Fatty Acids, Nonesterified / Q000097:blood*; D006728:Hormones / Q000097:blood*; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D010100:Oxygen / Q000378:metabolism*; D055815:Young Adult
chemical_list: D005230:Fatty Acids, Nonesterified; D006728:Hormones; D010100:Oxygen
keywords: Growth hormone; Lipolysis; Supramaximal exercise; Systemic hypoxia