HIIT in the Real World: Outcomes from a 12-Month Intervention in Overweight Adults

Purpose Although high-intensity interval training (HIIT) and moderate-intensity continuous exercise have comparable health outcomes in the laboratory setting, effectiveness studies in real-world environments are lacking. The aim of this study was to determine the effectiveness of an unsupervised HIIT programme in overweight/obese adults over 12 months. Methods 250 overweight/obese adults could choose HIIT or current exercise guidelines of 30 minutes/day moderate-intensity exercise. HIIT participants received a single training session and were advised to independently perform HIIT 3x/week utilizing a variety of protocols. Mixed models, with a random effect for participant, compared differences in weight, body composition, blood pressure, aerobic fitness, physical activity and blood indices at 12 months, adjusting for relevant baseline variables. Results Forty-two percent (n=104) of eligible participants chose HIIT in preference to current guidelines. At 12 months, there were no differences between exercise groups in weight (adjusted difference HIIT vs conventional; 95% CI: -0.44kg; -2.5, 1.6) or visceral fat (-103cm3; -256, 49), although HIIT participants reported greater enjoyment of physical activity (p=0.01). Evidence of adherence to ≥2 sessions/week of unsupervised HIIT (from heart rate monitoring) declined from 60.8% at baseline to 19.6% by 12 months. Participants remaining adherent to HIIT over 12 months (23%) were more likely to be male (67% vs 36%, p=0.03), with greater reductions in weight (-2.7kg; -5.2 -0.2) and visceral fat (-292cm3; -483, -101) than non-adherent participants. Conclusions HIIT was well-accepted by overweight adults and opting for HIIT as an alternative to standard exercise recommendations led to no difference in health outcomes after 12 months. While regular participation in unsupervised HIIT declined rapidly, those apparently adherent to regular HIIT demonstrated beneficial weight loss and visceral fat reduction. Trial Registration Australian New Zealand Clinical Trials Registry (ACTRN12615000010594) Retrospectively registered Address for correspondence: Professor Rachael Taylor, Department of Medicine, University of Otago, PO Box 56, Dunedin 9054, New Zealand. Email: rachael.taylor@otago.ac.nz, Phone: +64 3 470 9180 The results of this study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation. The results of the present study do not constitute endorsement by the American College of Sports Medicine. Competing interests: The authors declare that they have no competing interests. Funding: The SWIFT Study was funded by the University of Otago. RWT is partially funded by a Fellowship from the Karitane Products Society (KPS) Limited. The funders had no role in the design of the study; the collection, analysis, and interpretation of the data; the writing of the manuscript; or the decision to submit the article for publication. Accepted for Publication: 10 April 2018 © 2018 American College of Sports Medicine

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