High-intensity interval training: Modulating interval duration in overweight/obese men.
BACKGROUND
High-intensity interval training (HIIT) is a time-efficient strategy shown to induce various cardiovascular and metabolic adaptations. Little is known about the optimal tolerable combination of intensity and volume necessary for adaptations, especially in clinical populations.


OBJECTIVE
In a randomized controlled pilot design, we evaluated the effects of two types of interval training protocols, varying in intensity and interval duration, on clinical outcomes in overweight/obese men.


METHODS
Twenty-five men [body mass index (BMI) > 25 kg · m(2)] completed baseline body composition measures: fat mass (FM), lean mass (LM) and percent body fat (%BF) and fasting blood glucose, lipids and insulin (IN). A graded exercise cycling test was completed for peak oxygen consumption (VO2peak) and power output (PO). Participants were randomly assigned to high-intensity short interval (1MIN-HIIT), high-intensity interval (2MIN-HIIT) or control groups. 1MIN-HIIT and 2MIN-HIIT completed 3 weeks of cycling interval training, 3 days/week, consisting of either 10 × 1 min bouts at 90% PO with 1 min rests (1MIN-HIIT) or 5 × 2 min bouts with 1 min rests at undulating intensities (80%-100%) (2MIN-HIIT).


RESULTS
There were no significant training effects on FM (Δ1.06 ± 1.25 kg) or %BF (Δ1.13% ± 1.88%), compared to CON. Increases in LM were not significant but increased by 1.7 kg and 2.1 kg for 1MIN and 2MIN-HIIT groups, respectively. Increases in VO2peak were also not significant for 1MIN (3.4 ml·kg(-1) · min(-1)) or 2MIN groups (2.7 ml · kg(-1) · min(-1)). IN sensitivity (HOMA-IR) improved for both training groups (Δ-2.78 ± 3.48 units; p < 0.05) compared to CON.


CONCLUSIONS
HIIT may be an effective short-term strategy to improve cardiorespiratory fitness and IN sensitivity in overweight males.
Applied Physiology Laboratory, Department of Exercise and Sport Science, University of North Carolina , Chapel Hill, NC , USA.
Abbie E
AE
Smith-Ryan
Malia N
MN
Melvin
Hailee L
HL
Wingfield
D000222:Adaptation, Physiological; D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D001823:Body Composition; D015992:Body Mass Index; D002318:Cardiovascular Diseases / Q000209:etiology / Q000517:prevention & control; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D007333:Insulin Resistance; D008055:Lipids / Q000097:blood; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000150:complications / Q000378:metabolism / Q000628:therapy*; D050177:Overweight; D010101:Oxygen Consumption; D010807:Physical Endurance; D005082:Physical Exertion; D010809:Physical Fitness; D010865:Pilot Projects; D013997:Time Factors
D001786:Blood Glucose; D007328:Insulin; D008055:Lipids
Exercise; VO2peak; body weight; insulin; lifestyle; metabolism; percent body fat