Background: Recently, high intensity interval training (HIIT) has emerged as a promising regimen for the management of type 2 diabetic subjects. However, there is no consensus on the best time for HIIT regarding nutritional status.

Purpose: to investigate the effect of fasted versus postprandial HIIT training on glycemic control in men with type 2 Diabetes Mellitus.

Methods: This study enrolled 123 subjects suffering from type 2 diabetes mellitus with ages between 40 and 60 years. Subjects were divided into 4 groups, The post-breakfast, post-lunch and post-dinner groups practiced HIIT 2h after breakfast, lunch, and dinner respectively. The HIIT program involved 3 sessions weekly for 12 weeks. Glycated hemoglobin, fasting blood glucose, fasting insulin, insulin sensitivity, body composition, and blood lipid values were evaluated pre- and post-intervention.

METHODS Study Design This study was performed as a randomized, controlled trial and included four groups. The study procedures were carried out in the department of physical therapy and health rehabilitation, Prince Sattam Bin Abdulaziz University.

Ethical consideration The study protocol was approved by the Standing Committee of Bioethics Research in Prince Sattam bin Abdulaziz University, Saudi Arabia (ID: SCBR-352/2024). The study was conducted in line with the principles of the Declaration of Helsinki. All study participants have signed a written informed consent form. The aim, procedures and potential risks of the study were explained to the study population.

Participants:

A total of 160 men with T2DM were recruited from nearby hospitals and clinics to participate in this study and 123 completed the study follow-up. A licensed physician performed the preliminary evaluation for all participants. Participants were instructed to maintain their medications, their usual dietary habits and usual physical activity throughout the study period.

Only men diagnosed with T2DM, aged 40-60 years and inactive (performing less than 150 min/week of moderate-intensity exercise for at least the last six months) were included in this study. Subjects treated with exogenous insulin, and those with cardiovascular or musculoskeletal diseases limiting participation in HIIT were excluded.

Eligible subjects were randomly assigned to one of four groups. The Fasted-group practiced HIIT prebreakfast in the fasted state (8-12 h fasting). The Post-breakfast, Post-lunch and Post-dinner groups practiced HIIT 2h after breakfast, lunch, and dinner respectively. The primary outcome was glycated hemoglobin (HbA1c). Body composition, fasting blood glucose, fasting insulin, insulin resistance and lipid values were also evaluated. The experimental period was twelve weeks, and all outcomes were measured pre- and post-intervention period.

Sample size calculation The sample size was determined based on an estimated effect size (d = 0.40), derived from changes in HbA1c% observed in Al-Rawaf's study. To reject the null hypothesis, the probability was set at 0.05, with a power of analysis at 90%, calculated using G*power 3.0.10 software (University of Dusseldorf, Dusseldorf, Germany). A total of 96 participants were initially recruited. However, the sample size was increased to 125 to account for an anticipated dropout rate of up to 30%.

Anthropometrics assessments:

All participants were assessed for body weight and height. A weight and height scale (Detecto, made in USA) was used. Body mass index (BMI) was calculated using the following formula:

BMI = weight (kg) / height (m)2 The waist circumferences of all subjects were measured as per instruction. The body fat percentage of each subject was evaluated using InBody 770 multifrequency bioelectrical impedance analysis scale (BIA) (Biospace, Cerritos, California).

Blood sampling and analysis:

Pre- and post-intervention blood samples were obtained from all participants after 12hours overnight fast. Venous blood samples were collected from antecubital vein around 8:00 am. The collected samples were centrifuged at 4°C for 10 min and then stored at -80°C for further analysis. Blood samples were analyzed for glucose, lipid profile including total cholesterol, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, plasma triglycerides (Hitachi Automatic Analyzer 7600 Hitachi, Tokyo, Japan). HbA1c levels were measured using a Tosoh G7 automatic analyzer (Tosoh Bioscience, Tokyo, Japan). Serum insulin levels were measured by ECLIA using an E-Insulin kit (Roche Diagnostics, Mannheim, Germany). To exclude the potential acute effects of the last exercise bout, postintervention blood samples were collected 48-72 h after the last exercise session. Serum low-density lipoprotein (LDL) cholesterol levels were calculated using the Friedewald formula.

Exercise test In order to determine exercise training intensity all subjects underwent performed an incremental maximal cardiopulmonary exercise test according to standard Bruce protocol to determine the peak heart rate. A stationary CPET system (Quark CPET, COSMED, Italy) on a motorized treadmill (h/p/cosmos, Pulsar 4.0, Nussdorf-Traunstein, Germany) was used to perform the test. The flow sensor was calibrated using a 3.0-L syringe. CO2 and O2 sensors were calibrated against known gases before each test. The test was terminated when subjects reached the point of volitional exhaustion. Reaching peak effort was confirmed when respiratory gas exchange ratio was ≥1.10, in combination with dyspnea, and leg and/or general fatigue.

Exercise protocol The subjects in the four groups performed 12 weeks of supervised HIIE program on a motorized treadmill (h/p/cosmos, Pulsar 4.0, Nussdorf-Traunstein, Germany) with a rate of three sessions weekly. The session commenced with a 5 min warming-up and concluded with a 5 min cooling down period. The exercise effort component consisted of 5 intervals of HIIT. Each interval continues for four min of HIIT with exercise intensity ranging from 75% to 90% of the peak heart rate. Each active recovery period between exercise intervals included moderate exercise at intensity of 50% to 60% of the peak heart rate. Every 3 weeks, the exercise intensity was increased by 5% starting with 75% of the HRmax in the first 3 weeks, 80% in the following 3 weeks and progressed to 90% the HRmax in the last 3 weeks. The subject's heart rate throughout the HIIT session was monitored using a polar heart rate monitor (Polar, Kempele, Finland).

Inclusion Criteria:

• Only men diagnosed with T2DM,
• Aged 40-60 years
• Inactive (performing less than 150 min/week of moderate-intensity exercise for at least the last six months)

Exclusion Criteria:

• Subjects treated with exogenous insulin
• Cardiovascular diseases limiting participation in HIIT
• Musculoskeletal diseases limiting participation in HIIT

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