PMID 33531522

Research
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Effects of very low volume high intensity versus moderate intensity interval training in obese metabolic syndrome patients: a randomized controlled study

Reljic D, Frenk F, Herrmann HJ, Neurath MF, Zopf Y

Question

The study investigated whether two extremely time-efficient interval training protocols, performed as HIIT or MIIT and requiring less than 30 minutes per week, improve VO2max and cardiometabolic risk profile in obese metabolic syndrome patients compared with an inactive control group.

Summary

This 12-week randomized controlled trial tested extremely low-volume interval training in adults with obesity and metabolic syndrome. Participants were assigned to high-intensity interval training (HIIT), moderate-intensity interval training (MIIT), or inactive control, with all groups receiving nutritional counseling. Both exercise groups trained twice weekly on cycle ergometers for 14 minutes per session. HIIT produced the largest improvements in cardiorespiratory fitness, metabolic syndrome severity, waist circumference, blood pressure, quality of life, enjoyment, and intention to continue, while MIIT still improved several health outcomes compared with control. No adverse events occurred during training.

Methodology

  • Sedentary adults with obesity, increased waist circumference, and metabolic syndrome abnormalities.
  • 117 participants.
  • Electronically braked cycle ergometer.
  • Work intervals: 1 minute.
  • Recovery: 1 minute low-intensity recovery.
  • Intensity: 80%-95% HRmax, progressed from 80%-85% in weeks 1-4 to 85%-90% in weeks 5-8 and 90%-95% in weeks 9-12; achieved 93 +/- 5% HRmax at interval ends.
  • 14 minutes.
  • 2 sessions/week.
  • 12 weeks.
  • 12-week randomized controlled trial with three analyzed arms: HIIT plus nutritional counseling, MIIT plus nutritional counseling, and inactive control with nutritional counseling.
  • VO2max, Maximal and ventilatory-threshold power, Metabolic syndrome z-score, and Blood pressure were tracked.

Outcomes

VO2max

Relative VO2max increased in HIIT from 21.9 +/- 5.3 to 25.1 +/- 5.4 mL/kg/min and in MIIT from 20.3 +/- 3.8 to 21.5 +/- 4.3, while control changed from 21.0 +/- 7.3 to 20.7 +/- 7.8.

Group-by-time interaction p < 0.001, eta-p2 = 0.36 for relative VO2max; HIIT p < 0.001 and MIIT p < 0.05 within group.

Improved

MetS z-score

MetS z-score decreased in HIIT from 3.30 +/- 3.79 to 1.48 +/- 3.10 and in MIIT from 2.77 +/- 3.93 to 1.58 +/- 3.85; control decreased nonsignificantly from 1.79 +/- 2.92 to 1.25 +/- 2.77.

Group-by-time interaction p < 0.027, eta-p2 = 0.08; HIIT p < 0.001 and MIIT p < 0.01 within group.

Improved

Blood pressure

HIIT reduced systolic BP from 144 +/- 16 to 133 +/- 11 mmHg and diastolic BP from 94 +/- 11 to 86 +/- 7; MIIT reduced systolic BP from 143 +/- 14 to 131 +/- 11 and diastolic BP from 90 +/- 7 to 85 +/- 8; control did not improve.

Group-by-time interaction: systolic BP p = 0.001, eta-p2 = 0.15; diastolic BP p = 0.006, eta-p2 = 0.11; mean arterial BP p = 0.001, eta-p2 = 0.15.

Improved

Body weight and waist circumference

All groups lost weight, without significant between-group differences. Waist circumference reductions were significantly greater in HIIT than control; HIIT changed from 117.2 +/- 20.0 to 110.8 +/- 17.9 cm, MIIT from 109.0 +/- 12.4 to 105.3 +/- 12.1, and control from 110.3 +/- 12.3 to 109.3 +/- 13.3.

Weight time effect p < 0.001; waist circumference group-by-time interaction p = 0.001, eta-p2 = 0.15.

Mixed

Glucose and lipid markers

The authors reported no significant changes in blood markers of glucose and lipid metabolism despite improvements in blood pressure and MetS z-score.

No clear change

Quality of life and enjoyment

EQ VAS improved in HIIT by 10% and MIIT by 8%, with no significant control change. Enjoyment was higher in HIIT than MIIT, and intention to continue was 97% in HIIT versus 58% in MIIT.

QoL time effect p < 0.001, W = 0.18; HIIT EQ VAS p < 0.001, MIIT p = 0.029; enjoyment HIIT vs MIIT p = 0.001.

Improved

Adherence and safety

Adherence was high in both exercise groups and no adverse events occurred during training sessions.

Adherence: HIIT 94.6 +/- 7.6%; MIIT 91.7 +/- 8.6%.

Improved

Insights

  • A 14-minute, twice-weekly cycling interval protocol can improve clinically relevant fitness and blood pressure outcomes in supervised obese MetS patients.
  • A lower-intensity MIIT variant may be a practical stepping stone for users who cannot or will not perform high-intensity intervals.
  • Exercise preserved/improved fitness and cardiometabolic outcomes more than nutritional counseling and modest weight loss alone.
  • Heart-rate guided progression over 4-week blocks is a useful programming pattern.

Limitations

  • No long-term adherence or long-term efficacy data.
  • Exercise sessions were closely supervised in a controlled setting.
  • Generalizability to unsupervised home exercise is uncertain.
  • The trial did not include a MICT comparison in the analyzed arms.
  • Blood glucose and lipid markers did not significantly improve.
  • Participants with several major conditions were excluded, limiting high-risk generalization.

Safety

  • No adverse events occurred at any point during training sessions.
  • Two control participants could not perform the post-intervention cycle ergometer test because of injuries unrelated to the study.
  • Authors state very low-volume HIIT can be safely applied to obese individuals at increased cardiometabolic risk provided medical clarification is carried out beforehand.