PMID 28386234

Research
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High-Intensity Interval Training in Normobaric Hypoxia Improves Cardiorespiratory Fitness in Overweight Chinese Young Women

Kong Z, Shi Q, Nie J, Tong TK, Song L, Yi L, Hu Y

Question

Does performing a 5-week low-volume cycling HIIT program in normobaric hypoxia improve cardiometabolic and body composition outcomes more than the same HIIT under normoxia in overweight Chinese young women?

Summary

In sedentary overweight Chinese young women, 5 weeks of cycling HIIT improved cardiorespiratory fitness and some lipid ratios. Performing the same HIIT under mild normobaric hypoxia produced larger gains in VO2peak and peak oxygen pulse than normoxia, but did not add benefits for body composition, fasting leptin, or serum lipids. A physician attended all tests and training sessions.

Methodology

  • Twenty-four sedentary overweight otherwise healthy Chinese young women completing normoxic or normobaric hypoxic cycling HIIT.
  • 24 participants.
  • Cycle ergometer in normobaric hypoxia.
  • Work intervals: 8 s maximal cycling effort.
  • Recovery: 12 s recovery with pedal frequency 20-30 rpm.
  • Intensity: Maximal efforts; FIO2 0.15; about 84-88% HRmax during training.
  • 20 min protocol plus warm-up/cool-down.
  • 4 sessions/week.
  • 5 weeks.
  • Double-blind randomized placebo-controlled training study comparing normoxic versus normobaric hypoxic HIIT.
  • VO2peak, Peak oxygen pulse, Body composition, and Serum lipid profile and leptin were tracked.

Outcomes

VO2peak

Both groups improved VO2peak, with larger gains under hypoxia.

VO2peak L/min time effect p<0.001, time x group p=0.041; NORM +11.8%, HYP +26.1% in abstract.

Improved

Peak oxygen pulse

Peak oxygen pulse improved more in hypoxia than normoxia.

Time effect p<0.001; group effect p=0.024; time x group p=0.022.

Improved

Serum lipid ratios

TC/HDL-C and TG/HDL-C ratios improved over time, but hypoxia did not add a significant lipid benefit.

TC/HDL-C time effect p=0.035; TG/HDL-C time effect p=0.027; no significant group effects.

Improved

Body composition and leptin

Weight, BMI, lean mass, fat mass, body fat percentage, regional composition, and fasting leptin did not significantly change.

Table 3 reports non-significant time and group x time effects for body composition and leptin.

No clear change

Insights

  • Very short cycling intervals can improve fitness quickly in sedentary overweight young women.
  • Hypoxia may increase VO2peak gains in a lab setting, but it did not improve body composition or serum lipids beyond normoxic HIIT.
  • Hypoxic HIIT needs oxygen saturation monitoring and medical supervision.

Limitations

  • Small sample size.
  • Only young Chinese women.
  • Dietary intake and activity were self-reported and sampled 3 days/week.
  • Short 5-week intervention.
  • Hypoxic stress appeared to attenuate over time.
  • Hypoxic chamber setting limits practical translation.

Safety

  • A physician attended all tests and training sessions.
  • HR and SpO2 were monitored before, during, and after HIIT.
  • No specific adverse events were reported in the extracted main text.