Carbohydrate Availability and microRNA Expression

Twelve, normal weight, healthy, physically active men and women will complete a glycogen depletion protocol, cycling at various intensities until failure. Participants will then consume a carbohydrate (CHO: 1 g/kg/hr) or an energy free control (CON) beverage matched for taste and color during the first 3-hr post glycogen depletion. For the remainder of the day participants will consume a diet designed to adequately (6.0 g CHO/kg/d) or inadequately (1.2 g CHO/kg/d) replenish glycogen stores. The following day participants will to complete 80-min of steady-state (~60% VO2peak) cycle ergometry consuming carbohydrate at a rate of 1.8 g/min enriched with a stable isotope of carbon to determine exogenous carbohydrate efficiency when glycogen stores are low or adequate at the onset of exercise.

Following a minimum 7-d washout period volunteers will return to the laboratory to complete the second arm of the investigation. To ensure glycogen stores are similar between volunteers on testing day, 48-hrs prior to testing all volunteers will complete a glycogen depletion protocol and then consume a diet providing 6.0 g/kg/d carbohydrate to replenish glycogen stores.

Inclusion criteria

• Men and women aged 18 - 39 years
• Weight stable (±5 lbs) for at least 2 months prior to the start of the study
• Body mass index (BMI) between 18.5-30 kg/m2
• Recreationally active based on assessment of physical activity history 2-4 days per week aerobic and/or resistance exercise
• Refrain from taking any NSAIDS (i.e., aspirin, Advil®, Aleve®, Naprosyn®, or any aspirin-containing product for 10 days before and at least 5 days AFTER each muscle biopsy. (*Tylenol® or acetaminophen is ok to use if needed for discomfort)
• Refrain from the use of alcohol and nicotine for the duration of the study
• Females must be on contraception (e.g., oral birth control, NuvaRing®, Depo Provera®, etc.)
• Supervisor approved leave status for federal civilian employees working within the US Army Natick Soldier Systems Center

Exclusion criteria

• Metabolic or cardiovascular abnormalities, gastrointestinal disorders (i.e., kidney disease, diabetes, cardiovascular disease, etc.)
• Disease or medication (i.e., diabetes medications, statins, corticosteroids, etc) that affects macronutrient utilization and/or the ability to participate in strenuous exercise
• Allergies or intolerance to foods (including but not limited to lactose intolerance/milk allergy), vegetarian practices, or medications (including, but not limited to, lidocaine or phenylalanine) to be utilized in the study
• Anemia (HCT < 38) and Sickle Cell Anemia/Trait
• Abnormal prothrombin time (PT)/ partial thromboplastin time (PTT) test or problems with blood clotting
• Present condition of alcoholism, use of nutritional/sports supplements, anabolic steroids, or other substance abuse issues
• Musculoskeletal injuries that compromise the ability to exercise
• Blood donation within 8 weeks of beginning the study
• Pregnancy