Effect of High-intensity Interval Training on Metabolic Fitness in Overweight Males.
Condition: Overweight and Obesity
MeSH terms: Overweight
Study type: Interventional

Summary: 
      Background and aims: The purpose of this study was to evaluate the effect of high intensity
      interval training (HIIT) on body composition, physical fitness, metabolic fitness and muscle
      histology in men with overweight or obesity compared to continuous aerobic training (CAT).

      Material and methods: 16 male participants with overweight/obesity (age range: 42 - 57 years,
      body mass index: 28 - 36 kg/m²) were randomized to HITT (n=8) or CAT (n=8). HIIT was composed
      of two sprint blocks of 10 minutes at ventilatory threshold (VT), within between a continuous
      block of 10 minutes, twice a week for 15 weeks. CAT was composed of three blocks of 10
      minutes continuous endurance training at VT. After 5 weeks, intensity was increased to 110%
      of VT. Changes in body composition, physical fitness (peakVO2 and anaerobic threshold (AT)),
      basal respiratory exchange ratio (bRER) and insulin sensitivity by oral glucose tolerance
      test were evaluated. Mitochondrial content was evaluated by transmission electron microscopy
      (TEM) in muscle biopsies.
    

Detailed description: 
      Participants:

      For this study, 16 adult males with overweight or obesity (BMI-range 28 - 36 kg/m2) were
      recruited and randomized in two experimental groups (high intensity training (n=8) and
      continuous moderate-intense aerobic training (n=8)). Randomization was done with the envelope
      method. Participants were excluded if they had diabetes (HbA1c>6,5%), severe musculoskeletal
      (eg osteoarthritis), cardiovascular (eg chronic heart failure) or respiratory (eg chronic
      obstructive pulmonary disease (COPD)) problems, based on medical files A signed informed
      consent was provided by all participants before study admission. The study was approved by
      the ethics committee of the Ghent University Hospital (B670201318620).

      Intervention:

      The intervention group performed a high intensity interval training [HIIT]. The HIIT group
      followed a 10-week training program. The participants exercised for 40 minutes, twice a week,
      under supervision of two physiotherapists. Each training session included a warming up
      [stretching of the large muscle groups and cardiovascular exercises at 30% of peak cycling
      power output for five minutes], a sprint interval block [10 minutes], continuous aerobic
      exercise [10 minutes], another sprint interval block [10 minutes] and cooling down
      [stretching of the large muscle groups and cardiovascular exercises at 30% of peak Watt for 5
      minutes]. For the first 5 weeks, each sprint interval block consisted of 10 sprint bouts
      [>100 r/min] of 15 seconds at a cycling resistance matching with the ventilatory threshold
      [VTR], alternated with 45 seconds relative rest [50 r/min at VTR]. Starting from week 6 until
      week 10, the intensity of sprinting and relative rest was increased up to 110% of VTR.

      Comparative group:

      The comparative group performed a continuous aerobic training [CAT] for 10 weeks, twice a
      week and 40 minutes per session [volume and frequency is equal to HIIT]. The protocol of the
      CAT group consisted of warming up [stretching of the large muscle groups and cardiovascular
      exercises at 30% of peak cycling power output for five minutes], continuous aerobic exercise
      training [3 times 10 minutes] and cooling down [stretching of the large muscle groups and
      cardiovascular exercises at 30% of peak cycling power output for five minutes]. During the
      continuous aerobic protocol [cycling or stepping] participants exercised for 10 minutes at a
      HR similar to the HR at VT [60 r/min], which was increased to 110% of VT from week 6 onwards.
      The training was supervised by two physiotherapists.

      In both exercise modes the participants cycled in the first and third block and cycled or
      stepped in the second block. The training programs were conducted in the Physiotherapy
      Department of the University Hospital of Ghent.

      Outcome variables:

      The quantification of all examined variables was performed by blinded assessors. All tests
      and measurements were conducted at the exercise laboratory of the Physiotherapy Department,
      Ghent University (maximal exercise test, metabolic flexibility) or at the Department of
      Endocrinology University Hospital Ghent (OGTT and muscle biopsy) or Department of
      Pathological Anatomy (muscle histology). Prior to all tests and measurements, participants
      were well informed and familiarized with the equipment and testing protocols. All
      participants from each group were tested on the same moment of day pre- and
      post-intervention. All participants maintained normal physical activity and dietary patterns,
      and refrained from exhaustive physical exercise three days prior to each experimental day
      Anthropometry Height was measured to the nearest 0.1 cm using a stadiometer (Holtain Ltd,
      Pembrokeshire, UK). Weight was measured to the nearest 0.1 kg on a digital balance scale
      (Seca, Germany) with the subject wearing lightweight clothing and no shoes. The body mass
      index (BMI) was calculated from weight and height.

      Physical fitness Maximal cardiopulmonary exercise test. Participants were tested on a
      computer-driven cyclo-ergometer (Marquette Case, Marquette Electronics, Milwaukee, WI, USA)
      using a ramped protocol (20 W/ min) starting at 40 W. Twelve-lead electrocardiogram and heart
      rate (HR ) were recorded continuously during the test, whereas blood pressure was measured
      with a manual sphygmomanometer every two minutes. Subjects were familiarized with the test
      procedure before baseline testing. Subjects were asked and encouraged to perform exercise
      testing until physical exhaustion or until the physician stopped the test because of severe
      adverse events, such as increasing chest pain, dizziness, potentially life threatening
      arrhythmias, clinically important ST-segment deviations, marked systolic hypotension or
      hypertension. Tests were classified as maximal when respiratory exchange ratio (RER)
      increased above1.1. Respiratory gas measurements were obtained by using a Metalyzer 3B
      (Cortex, Leipzig, Germany). Oxygen consumption (VO2), carbon dioxide production (VCO2),
      minute ventilation (VE), tidal volume, respiratory rate and mixed expiratory carbon dioxide
      concentration were measured continuously with mixed chamber analysis. Peak VO2 was expressed
      as the highest attained VO2 during the final 30 seconds of exercise according to the American
      Thoracic Society guidelines. The ventilator threshold (VT) was determined based on the
      metabolic equivalents of O2 and CO2 (VE/VO2 and VE/VCO2). The point at which the VE/VO2
      increased without an increase in VE/VCO2 was identified as the VT.

      Basal respiratory exchange ratio Participants had to lie supine for 30 minutes after an
      overnight fast in a quiet and thermo-neutral environment. Basal oxygen consumption and carbon
      dioxide production was measured with an automated respiratory gas analyzer using a mask
      (Metalyzer 3B; Cortex, Leipzig, Germany). The gas analyzer system was calibrated before every
      experiment. RER was calculated as VCO2/VO2. This ratio lies in an interval between 0,7 en 1,0
      indicating dominant fat oxidation to dominant carbohydrate oxidation.

      Oral glucose tolerance test (OGTT) At 8:00 A.M. , after a 10- to 12-h overnight fast,
      subjects received a 75-g OGTT. Blood samples were taken at -30, -15, 0, 30, 60, 90, and 120
      min for the measurement of plasma glucose and insulin concentrations. Insulin levels were
      determined using the immunoanalyzer COBAS e411 (Roche). Glucose was analysed by the
      hexokinase method (COBAS, Roche).

      To evaluate insulin sensitivity an OGTT-composite score was calculation based on the
      reference of Matsudoa et al.. This score is composed as 10,000/square root of (fasting
      glucose x fasting insulin) x (mean glucose x mean insulin during OGTT). The higher the score,
      the better the insulin sensitivity.

      Muscle biopsy After a 1-h rest period, a percutaneous needle biopsy sample was taken from the
      right vastus lateralis muscle with a biopsy gun (needle 14G) under local anesthetic through a
      2-mm incision in the skin (2-3 ml lidocaine) under the guidance of echography. Two muscle
      samples of 15 mg were taken and incubated in PG (Paraformaldehyde and Glutaaraldehyde) for
      transmission electron microscopy (TEM).

      Transmission Electron Microscopy TEM was used to determine IMCL and mitochondrial
      characteristics. Samples were viewed at 6,500× using a JEOL 1200EX TEM. Sixteen micrographs
      were acquired from 8 randomly sampled longitudinal sections of muscle fibers (2
      micrographs/fiber) from each individual muscle - one micrograph acquired near the cell
      surface representing the subsarcolemmal (SS) region and the other acquired of parallel
      bundles of myofibrils representing the intramyofibrillar (IMF) region. Lipid droplets and
      mitochondrial fragments were circled and converted to actual size using a calibration grid.
      For each set of 16 images, mean IMCL or mitochondrial size (µm2), total number of IMCL
      droplets or mitochondria per square micrometer of tissue (#/µm2) were calculated in the IMF
      and SS compartments by digital imaging software (Image Pro Plus, ver. 4.0; Media Cybernetics,
      Silver Springs, MD). The reference for SS space quantification was the cytoplasmic space
      between the sarcolemma and the first layer of myofibrils.

      Statistical analyses All data were analysed with a commercially available statistical
      software program (Statistical Package for the Social Sciences, SPSS 20.0, SPSS Chicago, IL,
      USA). Data are expressed as mean and standard deviation (SD). Due to the small sample size a
      non-parametric statistical evaluation was preferred. To evaluate pre-post differences within
      groups, a Wilcoxon test was performed. To evaluate pre-post differences between groups,
      differences between pre- and post-evaluation were calculated (pre minus post) and compared
      with a Mann Withney U test. Significance levels were set at P<0,05 for both tests. For the
      between group differences effect sizes were calculated based on Cohen's d values.
    

Intervention name(s): High intensity exercise training; Continuous exercise training
Intervention type(s): Other; Other
Intervention description(s): Exercise training using sprint interval exercise; Exercise training using continuous exercise at constant heart rate
Other intervention name(s): HIT; CAT
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Single (Outcomes Assessor)
Primary purpose: Treatment
Keywords: Physical fitness; Respiratory exchange ratio; Insulin sensitivity; High intensity interval training; Continuous exercise training