Carbohydrate Availability and microRNA Expression

This investigation will examine the impact of skeletal muscle glycogen stores on skeletal muscle and circulating microRNA expression and exogenous carbohydrate oxidation.

Primary Objective Determine the influence of carbohydrate availability (e.g., glycogen depletion and repletion) on skeletal muscle microRNA expression, and if changes in circulating microRNA are reflective of changes in skeletal muscle microRNA.

Secondary Objective Determine how initiation of exercise with adequate or low glycogen stores effects exogenous carbohydrate efficiency.

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.

Eligibility Criteria:
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