Effects of Exercise Training Intensity on Fitness and Insulin Sensitivity in African Americans

The High Intensity Exercise to Promote Accelerated Improvements in CardiorEspiratory Fitness (HI-PACE) Study

African Americans are at a substantially greater type 2 diabetes risk compared to Caucasians; however, very little data are available on the effects of exercise training on type 2 diabetes risk factors in at risk African Americans. The present proposal will evaluate the effects of 6 months of moderate versus vigorous intensity aerobic exercise training on fitness, insulin sensitivity, mitochondrial capacity, skeletal muscle oxidative/insulin sensitivity markers, adiposity, and quality of life in African Americans.

African Americans have a much greater risk of type 2 diabetes compared to Caucasians in the United States. Similarly, recent evidence has emerged that fitness level, a major risk factor for type 2 diabetes also tends to be lower in African Americans. Many scientific studies have shown that exercise training has a beneficial impact on fitness levels and a variety of other type 2 diabetes risk factors such as the reduction of glucose/insulin levels, and body fat Importantly, studies performed in mostly Caucasian populations suggest that exercise training at a vigorous intensity may promote greater improvements in type 2 diabetes risk factors compared to moderate intensity exercise, which may suggest that it has greater promise in reducing type 2 diabetes risk. However, few exercise training studies compare the health benefits of different exercise training programs (such as exercise intensity) in African Americans, which is clinically important due to their greater type 2 diabetes risk, and that fact that they are less likely to meet public health recommendations for physical activity compared to their Caucasian counterparts.

The High Intensity exercise to Promote Accelerated improvements in CardiorEspiratory fitness (HI-PACE) study will evaluate the effect of exercise intensity on cardiorespiratory fitness (CRF) and insulin sensitivity in obese (BMI: 30-45) African Americans (40-65 yrs.) with at least 1 additional T2D risk factor. Participants (n=60) will be recruited in collaboration with the ECU Center for Health Disparities, and subsequently randomized to moderate intensity (MOD-INT, n=20) or high intensity (HIGH-INT, n=20) aerobic exercise training, or to a control group (CON, n=20) for 24 weeks. Supervised exercise training will be performed at a heart rate associated with ~50% and ~75% of VO2 max in the MOD-INT and the HIGH-INT groups, respectively at the same exercise volume of 600 MET-minutes per week (consistent with public health recommendations). The primary outcome is the change in CRF, which will be assessed at baseline, mid-intervention, and follow-up. Insulin sensitivity will be measured via an intravenous glucose tolerance test at baseline and follow-up. Other secondary measures include mitochondrial oxidative capacity using infrared and measurements on muscle biopsies (PGC-1α and other indices of mitochondrial content), the expression of a protein involved with insulin action (GLUT-4 expression) in skeletal muscle as well as systemic inflammation, adiposity, quality of life and exercise enjoyment measures.

Inclusion Criteria:

• African American
• Body mass index 30-45 kg/m2
• sedentary/low active (step count ≤ 6,500 step/day)
• capable and willing to give written informed consent and understand exclusion criteria
• willingness to accept group assignment from randomization
• No resistance training and no structured aerobic exercise for > 20 minutes per day, 3+ days per week, for the last 6 months
• conditions that are contraindicated for exercise training

Exclusion Criteria:

• Resting blood pressure > 180 mm Hg systolic and/or >100 mm Hg diastolic; individuals on blood pressure medications meeting the blood pressure criteria are eligible
• Diagnosis of type 1 or 2 diabetes, and/or fasting glucose >125 mg/dL
• Medication for the treatment of type 1 or type 2 diabetes
• Bariatric surgery including gastric banding or bypass (potential effects on energy intake)
• Factors that may limit adherence to intervention or affect conduct of the trial
• Unable or unwilling to communicate with staff
• Failure to complete run-in or baseline testing
• Hospitalization for depression or severe mental illness in the last 6 months
• Not physically capable of performing the exercise required of the study protocol
• Consuming more than 14 alcoholic beverages per week
• Plan to be away from the Pitt County area more than 3 weeks in the next 3 months
• Lack support from a primary health care provider or family members
• Significant weight loss in the past year (> 20 pounds) or are currently using weight loss medications.
• Current diagnosis of schizophrenia, other psychotic disorders, or bipolar disorder
• Another member of the household who is currently a participant or staff member of this study
• Other temporary intervening event, such as sick spouse, or bereavement
• Other medical, psychiatric, or behavioral limitations that may interfere with study participation or the ability to follow the intervention protocol
• Underlying diseases or conditions likely to limit lifespan and/or affect the safety of the intervention
• Cancer requiring treatment in the past 5 years with anything but excellent prognosis
• Self-reported HIV, tuberculosis, Hepatitis B, or Hepatitis C
• History or evidence of serious arrhythmias, cardiomyopathy, congestive heart failure, aortic aneurism, myocardial infarction or heart transplantation
• Renal disease: urine protein > 100 mg/dl, serum creatinine ≥ 1.5 mg/dl or currently receiving dialysis.
• Auto-immune diseases (such as Lupus, Multiple Sclerosis, Graves' disease, or Rheumatoid arthritis)
• Chronic obstructive lung disease, peripheral vascular disease or angina that limits ability to follow exercise protocol
• History of stroke or transient ischemic attack
• History of vascular aneurysms
• History of bleeding disorders
• Pregnancy or plans to become pregnant
• Dieting or plans to diet, or in a weight loss program
• Any other medical condition or disease that is life threatening or that can interfere with or be aggravated by exercise.