title: Cardiac autonomic function and high-intensity interval training in middle-age men.
abstract: OBJECTIVE
  The effects of short-term high-intensity interval training (HIT) on cardiac autonomic function are unclear. The present study assessed cardiac autonomic adaptations to short-term HIT in comparison with aerobic endurance training (AET).
  
  
  METHODS
  Twenty-six healthy middle-age sedentary men were randomized into HIT (n = 13, 4-6 × 30 s of all-out cycling efforts with 4-min recovery) and AET (n = 13, 40-60 min at 60% of peak workload) groups, performing six sessions within 2 wk. The participants underwent a 24-h ECG recording before and after the intervention and, additionally, recorded R-R interval data in supine position (5 min) at home every morning during the intervention. Mean HR and low-frequency (LF) and high-frequency (HF) power of R-R interval oscillation were analyzed from these recordings.
  
  
  RESULTS
  Peak oxygen consumption (V˙O2peak) increased in both groups (P < 0.001). Compared with AET (n = 11), HIT (n = 13) increased 24-h LF power (P = 0.024), tended to increase 24-h HF power (P = 0.068), and increased daytime HF power (P = 0.038). In home-based measurements, supine HF power decreased on the days after HIT (P = 0.006, n = 12) but not AET (P = 0.80, n = 9) session. The acute response of HF power to HIT session did not change during the intervention.
  
  
  CONCLUSIONS
  In conclusion, HIT was more effective short-term strategy to increase R-R interval variability than aerobic training, most probably by inducing larger increases in cardiac vagal activity. The acute autonomic responses to the single HIT session were not modified by short-term training.
authors.affiliation: 1Department of Exercise and Medical Physiology, Verve Research, Oulu, FINLAND; 2Department of Applied Sciences, London South Bank University, London, UNITED KINGDOM; 3Turku PET Centre, University of Turku and Turku University Hospital, Turku, FINLAND; 4Paavo Nurmi Centre, Turku, FINLAND; 5Research Centre of Applied and Preventive Cardiovascular Medicine, University of Turku, Turku, FINLAND; and 6Institute of Clinical Medicine, University Hospital and University of Oulu, Oulu, FINLAND.
authors.forename: Antti M
authors.initials: AM
authors.lastname: Kiviniemi
authors.forename: Mikko P
authors.initials: MP
authors.lastname: Tulppo
authors.forename: Joonas J
authors.initials: JJ
authors.lastname: Eskelinen
authors.forename: Anna M
authors.initials: AM
authors.lastname: Savolainen
authors.forename: Jukka
authors.initials: J
authors.lastname: Kapanen
authors.forename: Ilkka H A
authors.initials: IH
authors.lastname: Heinonen
authors.forename: Heikki V
authors.initials: HV
authors.lastname: Huikuri
authors.forename: Jarna C
authors.initials: JC
authors.lastname: Hannukainen
authors.forename: Kari K
authors.initials: KK
authors.lastname: Kalliokoski
mesh_terms: D000328:Adult; D001016:Aortic Bodies / Q000378:metabolism; D001341:Autonomic Nervous System / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption; D056152:Respiratory Rate; D013997:Time Factors