Low-frequency High-Intensity Interval Training in Overweight or Obese Young Adults
Condition: Overweight and Obesity
MeSH terms: Overweight
Study type: Interventional

Summary: 
      Background: The relationship between the frequency of high-intensity interval training (HIIT)
      and the resultant adaptations is largely unclear. Purpose: This study examined the effects of
      different frequencies of HIIT compared to moderate-intensity continuous training (MICT) on
      body composition and cardiovascular biomarkers in overweight or obese adults. Methods: This
      study was a randomized, controlled, single-blinded trial. Fifty-six overweight or obese men
      aged between 18 and 30 years were randomly assigned to no-intervention control (CON; n=14),
      MICT performed thrice weekly (MICT×3/wk; n=9), HIIT performed thrice weekly (HIIT×3/wk;
      n=14), HIIT performed twice weekly (HIIT×2/wk; n=10), and HIIT performed once weekly
      (HIIT×1/wk; n=9). Each HIIT session consisted of 12 × 1-min bouts at 90% heart rate reserve
      (HRR), interspersed with 11 × 1-min bouts at 70% HRR (HIIT×3/wk: 69 min/wk; HIIT×2/wk: 46
      min/wk; HIIT×1/wk: 23 min/wk). Aerobic capacity, resting heart rate, body composition, waist
      circumference, blood pressure, endothelial function, fasting blood glucose and lipids,
      circulatory adipokines and inflammatory biomarkers were examined at baseline, after 4 weeks
      and 8 weeks of intervention.
    

Detailed description: 
      Individuals who fulfilled the following inclusion criteria were invited to participate in the
      present study: 1) Chinese male; 2) aged 18-30 years; and 3) overweight or obesity, defined as
      BMI ≥23 kg/m2 (classification of overweight for Hong Kong adults according to Department of
      Health, Hong Kong SAR Government) (13). Subjects were excluded if they had: 1) chronic
      medical and health condition such as cardiovascular diseases, diabetes, neurological disease,
      musculoskeletal disorder, cancers, and autoimmune diseases; 2) hypertension (blood pressure
      >140/90 mmHg); 3) contraindications to participating in physical exercise; 4) any
      pre-existing medical or physical issues that affected the experimental test; 5) physically
      active (i.e., >3 hours of moderate-intensity exercise weekly) or 6) lean overweight
      population (BMI ≥23 kg/m2, but percent body fat ≤20%) according to the BMI data corresponding
      to bioelectrical impedance estimated percent body fat cut-off value among Hong Kong Chinese
      adults.

      Of those who were screened, 103 Chinese young adults were eligible to participate in this
      study. They were provided with written and verbal information on the study protocol and the
      possible associated discomforts and risks followed by obtaining their written informed
      consent to participate in this study. The study protocol and consent form were approved by
      the Human Subjects Ethics Sub-Committee of The Hong Kong Polytechnic University (ethics
      approval reference number: HSEARS20160927005-01).

      This study was a single-blind, randomized, controlled trial. Subjects were randomly assigned
      to 1) no-intervention control (CON), 2) MICT performed thrice weekly (MICTx3/wk), 3) HIIT
      performed thrice weekly (HIITx3/wk), 4) twice weekly (HIITx2/wk), and 5) once weekly
      (HIITx1/wk). All subjects were instructed to maintain their usual daily activities. Outcome
      measures including aerobic capacity, body composition, blood pressure, resting heart rate,
      endothelial function, arterial stiffness, fasting glucose, lipids markers, adipokine marker,
      and inflammatory marker were assessed at baseline, 4 weeks and 8 weeks after the
      intervention.
    

Intervention name(s): Exercise intervention
Intervention type(s): Behavioral
Intervention description(s): HIIT groups performed 30-meter shuttle runs on a rooftop covered field whereas MICT group ran on a footpath with an overall flat and non-slippery road surface. All training sessions were preceded by a 5-minute self-pace warm-up jogging and ended with a 5-minute self-pace jogging or walking cool-down. Each session of MICT consisted of 30 minutes of continuous exercise at an intensity of 60% of heart rate reserve (HRR); [i.e., (maximal HR - resting HR) × intensity + resting HR]. For each HIIT session, the intensity was set at 90% HRR for high-intensity bouts, interspersed with active recovery at 70% HRR. All exercise sessions were supervised by qualified athletic coach or strength and conditioning coach.
Allocation: Randomized
Intervention model: Parallel Assignment
Intervention model description: 5 groups ×3 times factorial design
Masking: Single (Participant)
Primary purpose: Treatment
Keywords: HIIT; Exercise frequency; Exercise intensity