Acute Hormonal Responses Before and After 2 Weeks of HIT in Well Trained Junior Triathletes

Int J Sports Med. 2014 Apr;35(4):316-22. doi: 10.1055/s-0033-1353141. Epub 2013 Sep 30.


The aim was to compare the acute hormonal response to a single HIT session at the beginning and end of a HIT shock microcycle. 13 male junior triathletes (15.8±1.8 yrs.) performed 16 HIT sessions within a 2 week period. Venous blood samples were collected before and after the first and last HIT session. Significant increases in cortisol (first session +89.7%; last session +70.3%) and hGH (first session +435.1%; last session +314.6%) concentrations were observed after both training sessions (P<0.05). The acute responses of cortisol, hGH, T3, and fT3 were not different between the first and last HIT sessions (P=1.00). Although no acute changes in testosterone were detected after the training sessions, testosterone concentrations were significantly higher at all time points (62.6-80.1%) during the last compared to first training session (P≤0.001). Findings from the present study reveal that 16 sessions of HIT led to significant increases in baseline concentrations of serum testosterone. This might indicate a heightened anabolic state even in junior triathletes. Based on the hormonal data, we conclude that at the end of this 2 week microcycle no familiarization effect was evident and that the training stimulus produced by HIT was still great enough to "stress" the athletes and induce positive training adaptations.

MeSH terms

  • Adaptation, Physiological*
  • Adolescent
  • Athletic Performance / physiology
  • Bicycling / physiology
  • Hormones / blood*
  • Human Growth Hormone / blood
  • Humans
  • Hydrocortisone / blood
  • Male
  • Oxygen Consumption
  • Physical Education and Training / methods*
  • Physical Endurance / physiology*
  • Running / physiology
  • Swimming / physiology
  • Testosterone / blood
  • Triiodothyronine / blood


  • Hormones
  • Triiodothyronine
  • Human Growth Hormone
  • Testosterone
  • Hydrocortisone