HIIT in Isolated IFG: A Proof-of-Concept Study

This pilot randomized controlled trial will involve 34 physically inactive adults aged 35-65 years with overweight or obesity and isolated impaired fasting glucose (i-IFG). The study aims to assess the feasibility of recruiting and retaining participants, implementing study procedures, and evaluating the acceptability of a high-intensity interval training (HIIT) intervention. Additionally, it will investigate the preliminary efficacy of HIIT in reducing fasting plasma glucose levels and addressing the pathophysiology of i-IFG.

This 1:1 proof-of-concept randomized controlled trial (RCT) will involve 34 physically inactive adults aged 35-65 years who are overweight or obese and have isolated impaired fasting glycemia (i-IFG). Potentially eligible individuals identified through Emory's MyChart electronic health care records system will undergo initial screening via phone calls. Individuals meeting the eligibility criteria will be invited to the Georgia Clinical and Translational Science Alliance at Emory University Hospital in Atlanta for further assessment. During their visit, participants will complete questionnaires, undergo an oral glucose tolerance test, and provide blood samples for insulin. Individuals identified with i-IFG will be randomized into the intervention or control groups.

Individuals assigned to the intervention group will participate in supervised high-intensity interval training (HIIT) sessions using stationary Spin cycle ergometers, in groups of five or fewer. They will wear continuous glucose monitoring (CGM) devices for 10 days before the intervention, throughout the 8-week intervention period, and for 10 days post-intervention. The intervention will be conducted three times a week for eight weeks at the Aerobic Exercise Laboratory in the Rehabilitation Hospital at Emory University. Control participants will be instructed to refrain from engaging in intense physical activities during the study period and will also wear CGM devices for the same duration. All participants will receive instructions to maintain a eucaloric diet throughout the study.

At baseline and after eight weeks, all participants will undergo physical measurements (anthropometrics, blood pressure, and body composition) as well as biochemical measurements (glucose and insulin levels). Additionally, participants in the intervention group will be invited to participate in qualitative in-depth interviews both before and after the HIIT intervention and will complete an intervention acceptability questionnaire upon completion.

The primary outcomes include feasibility metrics, measures of intervention feasibility, acceptability, and appropriateness, and participants' experiences, perceptions, and satisfaction with the HIIT intervention, as well as facilitators and barriers to participation. Secondary outcomes include: 1) Between-group differences in changes from baseline to 8 weeks in mean fasting plasma glucose and insulin levels, indices of β-cell function and insulin resistance, and physical measurements; and 2) CGM metrics: a) Between-group differences in the proportion of time and mean time spent in nocturnal (00:00-06:00) \[58\] normoglycemia (60 to \<100 mg/dl) during the 8-week intervention period and the 10 days following the intervention; b) Within-participant differences in the proportion of time and mean time spent in nocturnal (00:00-06:00) normoglycemia (60 to \<100 mg/dl) between exercise and non-exercise days during the 8-week intervention period.

Eligibility Criteria:
Inclusion criteria:

1. Males and females aged 35-65 years
2. Any race or ethnicity
3. BMI ≥25 kg/m2 (≥23 kg/m2 if Asian decent)
4. Physically inactive (\<150 min of moderate-intensity or \<75 min of vigorous-intensity aerobic physical activity/week)
5. Will be residing in the same location until completion of the study
6. Isolated impaired fasting glucose on the OGTT: FPG 100-125 mg/dl and 2-hr plasma glucose \<140 mg/dl

Exclusion criteria:

1. History of diabetes
2. Regular exercise training in the past 6 months
3. Enrolled in weight loss programs in the past 6 months
4. Following a specific diet (e.g., ketogenic, Mediterranean)
5. Pregnant women
6. Breastfeeding
7. Smokers
8. Taking medications known to affect glucose tolerance (e.g., steroids)
9. Taking beta-blockers and calcium channel blockers
10. Taking weight loss medications
11. Underwent bariatric surgery
12. Anemia
13. History of chronic illnesses (e.g., stroke)

Individuals satisfying the eligibility criteria will undergo an OGTT (0, 30, 120 min), and those diagnosed with i-IFG (FPG 100 or 110-125 mg/dl and 2-hr PG \<140 mg/dl) will be recruited to the study.