Individuals with obesity and particular type 2 diabetes have abnormally high levels of fat in liver cells and are at increased risk for cardiovascular and liver-related mortality. Prior research has shown that caloric restriction, exercise, and behavior modification can help lower hepatic fat levels in these individuals. Additional research has also shown that exercise independent of weight loss can reduce hepatic fat content in obese humans. The current exercise guidelines do not specify what type or what intensity of exercise is required to induce such reductions in hepatic fat. Thus, the purpose for doing this study is to determine if there are differential effects on liver fat with 4 wk of high intensity intermittent exercise compared with continuous moderate exercise in obese individuals.

Subjects will complete a liver spectroscopy scan to ensure that they have 5% body fat. Subjects passing screening will then have body composition measurement and aerobic capacity (VO2 peak) measured. Blood samples will also be taken and subjects will complete an oral glucose tolerance test. Upon completion of this testing subjects will be randomized into one of two groups: Continuous moderate exercise group or High-intensity interval exercise .

Continuous moderate exercise group (CME): Subjects will perform a 5-10 minute warm-up at 50% VO2peak. Thereafter, the intensity of exercise will be increased to 70% VO2peak by increasing the speed and incline of the treadmill. Subjects will exercise at this intensity for 60 minutes. A 5 minute cool-down (50% VO2peak).

High-intensity interval exercise (HIIE): Subjects will perform 5-10 minute warm-up (50% VO2peak). Following the warm-up, the speed and incline of the treadmill will be increased so that subjects reach an exercise intensity that corresponds to 90% Heart Rate max. Subjects will exercise at this intensity for 4 minutes, after which the treadmill speed and incline will be reduced to an intensity between 55% and 70% Heart Rate max for 3 minutes. This procedure will be replicated three additional times for a total of four intervals/recovery periods. The total exercise commitment will be ~45 minutes.

After 4 wk of exercise training all subjects will undergo all of the initial testing.

Inclusion Criteria:

• Overweight or obese with a body mass index between 30-45 kg/m2.
• No known cardiovascular, kidney, or liver disease.
• No extreme hypertension (>160 mm Hg systolic and/or > 100 mm Hg diastolic).
• Not being treated with exogenous insulin.
• No history of surgery for weight loss and weight stable for prior 3 months (weight change < 3 kg).
• Non-exerciser (< 20 minutes of exercise 2 days per week).
• Between 21-60 yr of age

Exclusion Criteria:

• History of alcohol use (> 20 g/day for males and > 10 g/day for females)
• Kidney or liver disease.
• Extreme hypertension >160 mm Hg systolic and/or > 100 mm Hg diastolic.
• Waist measurement greater than 60"
• Magnetic Resonance Spectroscopy scan with less than 5% of liver fat
• A history of surgery for weight loss.
• Exerciser (>20 minutes of exercise at least 2 days per week)
• Pregnant or lactating
• <21 or >60 yr of age