HIIT Versus MICT on Abdominal Fat Mass and Lipid Oxidation in Postmenopausal Women (MATISSE)

Postmenopausal women, as men, are more prone to central or android obesity than premenopausal women. Abdominal fat mass accumulation is associated with an increase of cardiovascular disease (CVD) risk.

Most exercise programs designed for weight loss have focused on about 30 min several times per week of moderate intensity continuous training (MICT). Disappointingly, such exercise programs have led to either none or low fat loss. Accumulating evidence suggests that high intensity interval training (HIIT) should be an effective exercise protocol for reducing body fat of overweight individuals, especially at the abdominal level.

Resistance Training (RT) is associated with increased muscle mass and strength gain in main muscles groups. Thus, RT seems to be an interesting strategy to fight against deconditioning and autonomy loss with age. Development of muscle mass enhances resting metabolism rate. Thus, RT could raise daily energy expenditure ie. substrates' oxidation including lipids.

The aim of our study was to compare the effects of a 12-week moderate intensity continuous training (MICT) program with high intensity interval training (HIIT) program combined or not with a resistance training (RT) program on total abdominal and visceral fat mass and substrate utilization in postmenopausal women.

It is hypothesized that HIIT compared to MICT program would result in significantly greater whole body and regional fat mass losses (abdominal and visceral) and would improve lipid oxidation at rest and during prolonged moderate exercise. It is also hypothesized that HIIT associated with RT could be the best strategy to reduce fat mass.

Overweight and obesity are dramatically spreading worldwide, and these trends are occurring in both developed and developing countries. Fat mass and more particularly abdominal fat mass is related to the development of cardio-vascular diseases (CVD). Postmenopausal women, as men, are more prone to central or android obesity.

Most exercise programs designed for weight loss have focused on about 30 min several times a week of moderate intensity continuous training (MICT). Disappointingly, such exercise programs have led to either none or low fat losses. Accumulating evidence suggests that high intensity interval training (HIIT) could be an effective exercise protocol for reducing adipose tissue of overweight individuals, especially at the abdominal level. HIIT involves brief high-intensity, anaerobic exercise followed by brief but slightly longer bouts of very low-intensity exercise.

Resistance training (RT) program are currently proposed in order to reduce fat mass / preserve fat-free mass. Their beneficial effects have been demonstrated, especially in the elderly. Through development (or maintenance) of muscle mass, RT increases resting metabolism rate, daily energy expenditure, and substrate (fatty acids) oxidation.

The aim of the study was to compare the effects of a 12-week moderate intensity continuous training (MICT) program with high intensity interval training (HIIT) combined or not with resistance training (RT) program on total, abdominal and visceral fat mass and substrate utilization at rest and during exercise in postmenopausal women.

36 postmenopausal women will be randomly assigned to MICT (n= 12) or HIIT (n= 12) or HIIT + RT (n= 12) group. Subjects performed three sessions per week during 12 weeks, on bicycle.

MICT: For the MICT protocol, each subject performed 35 min at 50% maximal aerobic power (MAP).

HIIT: For the HIIT protocol, each subject performed repeated cycles of sprinting for 8 s and pedaling slowly for 12 s (between 20 and 30 rpm) for a maximum of 60 repeats per session.

HIIT+RT: For the HIIT+RT protocol, each subject performed HIIT protocol. Then they performed a single set of 8 exercises with 1 or 2min resting period between exercises. Each set consisted of 8-12 repetitions at about 80% maximum repetition (MR).

Total body and regional fat content will be measured using dual-energy x-ray absorptiometry (DEXA) before and after the intervention (3 months).

The investigators will examine the effects of HIIT, MICT and HIIT + RT programs on:

* Total fat mass (and appendicular fat mass) (DEXA)
* Total fat free mass (and appendicular fat free mass) (DEXA)
* Glycemic profile (plasma HbA1c, plasma glucose)
* Lipid profile (TG, HDL, LDL, total cholesterol)
* Substrates oxidation at rest and during moderate exercise (40min, 50% of maximal oxygen consumption VO2 max)

Statistical analysis

Appropriate sample size has been calculated given previous results about fat mass loss during HIIT in women and considering the dropouts observed in this type of protocol.

Gaussian distribution of the data will be tested by the Kolmogorov-Smirnov test. Data will be presented as mean ± standard deviation (SD). Comparisons between groups will be made with Mann \& Whitney U test or ANOVA when appropriate. Relationships between data will be assessed by Pearson correlation. Significance will be accepted at the p\<0.05 level. Statistical procedures will be performed using Statistica software.

Eligibility Criteria:
Inclusion Criteria:

* Postmenopausal women (55- 82 years)
* BMI ≥ 25 and \< 40
* Able to follow an exercise protocol
* Eating behavior and physical activity stable since at least 3 month

Exclusion Criteria:

* Subject not able to perform exercise after medical examination
* Subject not able to perform bicycle exercise (pains)
* Chronic infection
* Use of β-blocker
* Medical treatment that could interfere with the different outcome measures
* Hormonal Replacement Therapy (HRT)
* Regular consumption of alcohol
* Refusal to sign the consent form