title: Effectiveness of two weeks of high-intensity interval training on performance and hormone status in adolescent triathletes.
abstract: BACKGROUND
  Weekly training volumes for triathlete are typically higher and may cause fatigue and musculoskeletal injury risk. High-intensity interval training (HIT) is a potent time-efficient strategy to induce adaptations normally associated with traditional endurance training. Therefore, the aim of this study was to investigate the effect of two weeks of in-season HIT on exercise capacity and hormonal responses in young triathletes.
  
  
  METHODS
  Twelve adolescent triathletes performed 18 sessions of HIT over 2 weeks including swim, cycle, and run events. The 6-day training blocks were separated by 1 day of recovery. Pre- and post-training, peak oxygen uptake (VO2peak) and exercise performance were assessed, and blood samples were obtained to detect changes in hormone and metabolite levels.
  
  
  RESULTS
  VO2peak was significantly higher (P=0.02) post-training (56.4±8.1 mL·min-1·kg-1) versus pre-training (55.1±7.5 mL·min-1·kg-1). Mean power and total work during 6×10 s repeated-sprint tests significantly increased (P=0.03) after HIT. Additionally, 750 m swim time (pre- vs. post: 689.7±102.5 s vs. 662.0±75 s, P=0.01) and 20 km cycling time (pre- vs. post: 1856.6±274.8 s vs. 1705.4±266.8 s, P=0.02) were significantly lower post-training compared to pre-training, but there was no significant difference in 5 km run time after HIT (pre- vs. post: 1315.8±81.3 s vs. 1292.0±112.9 s, P=0.31). In contrast to pre-training, ammonia concentration was significantly increased (P<0.01) and creatine kinase concentration was significantly decreased (P=0.02) post-training.
  
  
  CONCLUSIONS
  These findings suggest that two weeks of HIT using HRpeak as a monitor of physiological intensity improved VO2peak, sprint performance, and triathlon-specific performance in adolescent triathletes and attenuated levels of muscle damage.
authors.affiliation: Center for General Education, National Sun Yat-Sen University, Kaohsiung, Taiwan - karenlee1129@gmail.com.
authors.forename: Chia-Lun
authors.initials: CL
authors.lastname: Lee
authors.affiliation: Department of Sports Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan.
authors.forename: Mei-Chich
authors.initials: MC
authors.lastname: Hsu
authors.affiliation: Department of Kinesiology, California State University-San Marcos, San Marcos, CA, USA.
authors.forename: Todd A
authors.initials: TA
authors.lastname: Astorino
authors.affiliation: Chinese Taipei Triathlon Association, Taipei, Taiwan.
authors.forename: Ta-Wei
authors.initials: TW
authors.lastname: Liu
authors.affiliation: Department of Sports Medicine, China Medical University, Taichung, Taiwan.
authors.forename: Wen-Dien
authors.initials: WD
authors.lastname: Chang
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000293:Adolescent; D000328:Adult; D001642:Bicycling / Q000502:physiology*; D005221:Fatigue / Q000209:etiology; D000072696:High-Intensity Interval Training / Q000379:methods*; D006728:Hormones / Q000097:blood*; D006801:Humans; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology; D010807:Physical Endurance / Q000502:physiology*; D012420:Running / Q000502:physiology*; D013550:Swimming / Q000502:physiology*; D055815:Young Adult
chemical_list: D006728:Hormones