Efficacy of high-intensity, low-volume interval training compared to continuous aerobic training on insulin resistance, skeletal muscle structure and function in adults with metabolic syndrome: study protocol for a randomized controlled clinical trial (Intraining-MET)

Abstract

Background: Evidence of the efficacy of high-intensity, low-volume interval training (HIIT-low volume) in treating insulin resistance (IR) in patients with metabolic disorders is contradictory. In addition, it is unknown whether this effect is mediated through muscle endocrine function, which in turn depends on muscle mass and fiber type composition. Our aims were to assess the efficacy of HIIT-low volume compared to continuous aerobic exercise (CAE) in treating IR in adults with metabolic syndrome (MS) and to establish whether musclin, apelin, muscle mass and muscle composition are mediators of the effect.

Methods: This is a controlled, randomized, clinical trial using the minimization method, with blinding of those who will evaluate the outcomes and two parallel groups for the purpose of showing superiority. Sixty patients with MS and IR with ages between 40 and 60 years will be included. A clinical evaluation will be carried out, along with laboratory tests to evaluate IR (homeostatic model assessment (HOMA)), muscle endocrine function (serum levels of musclin and apelin), thigh muscle mass (by dual energy x-ray absorptiometry (DXA) and thigh muscle composition (by carnosine measurement with proton magnetic resonance spectroscopy (1H-MRS)), before and after 12 weeks of a treadmill exercise program three times a week. Participants assigned to the intervention (n = 30) will receive HIIT-low volume in 22-min sessions that will include six intervals at a load of 90% of maximum oxygen consumption (VO2 max) for 1 min followed by 2 min at 50% of VO2 max. The control group (n = 30) will receive CAE at an intensity of 60% of VO2 max for 36 min. A theoretical model based on structural equations will be proposed to estimate the total, direct and indirect effects of training on IR and the proportion explained by the mediators.

Discussion: Compared with CAE, HIIT-low volume can be effective and efficient at improving physical capacity and decreasing cardiovascular risk factors, such as IR, in patients with metabolic disorders. Studies that evaluate mediating variables of the effect of HIIT-low volume on IR, such as endocrine function and skeletal muscle structure, are necessary to understand the role of skeletal muscle in the pathophysiology of MS and their regulation by exercise.

Trial registration: NCT03087721 . High-intensity Interval, Low Volume Training in Metabolic Syndrome (Intraining-MET). Registered on 22 March 2017, retrospectively registered.

Keywords: Aerobic exercise; Exercise training; Glucose metabolism disorders; Hyperinsulinemia; Insulin resistance; Interval training; Metabolic syndrome; Myokines; Risk factors; Skeletal muscle.

Conflict of interest statement

Ethics approval and consent to participate

The Research Ethics Committee of the Faculty of Medicine at Universidad de Antioquia in Medellín approved the study protocol (minutes number 013 from 26th September 2013). The Research Ethics Committee IPS-Universitaria at Universidad de Antioquia in Medellín, Colombia approved the study protocol (minutes number 097 from 22nd June 2016). All patients will sign the informed consent to participate.

Consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

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Figures

Fig. 1

General design of the study, schedule of enrollment, intervention and assessment*. a After signing the informed consent, the patients will undergo medical and biochemical evaluation. Once inclusion/exclusion criteria are verified, recruited patients will be evaluated for muscle mass, fiber type composition of the vastus lateralis muscle (VLM), and cardio-respiratory physical capacity. Then, patients will be assigned to a high-intensity/low-volume interval training (HIIT-low volume) or continuous aerobic exercise training (CAE) intervention. A final reevaluation will be performed. b Evaluations during both enrollment and close out periods are expected to last 2 weeks. The intervention will last 12 weeks. HOMA-IR, Homeostatic Model Assessment-Insulin Resistance; HbA1c, glycated hemoglobin; IR, insulin resistance; MS, metabolic syndrome

Fig. 2

Training protocols for intervention. a High-intensity/low-volume interval training protocol scheme. b Continuous aerobic exercise protocol scheme. VO2 max, maximum oxygen consumption

Fig. 3

Conceptual model for the study of the effect of high-intensity/low-volume interval training or continuous exercise training on insulin resistance in patients with metabolic syndrome. The model considers mediator variables such as musclin and apelin, muscle mass and fiber type composition in the thigh; and confounding variables such as age, gender and body mass index