Core Services: Human Phenotyping: Physical Activity Lab Fueling Exercise

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Investigating the association between exercise capacity, fuel selection and metabolic health using metabolomics (IRB# HUM00089054)

Background: At rest and during low intensity exercise such as walking, fat is the primary fuel source. As exercise intensity increases, as in running, the body relies more heavily upon carbohydrates as an energy source. The point at which this shift from fat to carbohydrate occurs differs in fit vs. unfit individuals. Fit people metabolize (use) fat longer and at higher intensities than their less fit counterparts. We do not know why or how exactly this happens.

Purpose: The purpose of this study is to assess potential associations between exercise capacity (fitness), fuel selection and metabolic health. Fuel selection refers to the energy source your body uses during exercise – i.e. fat or carbohydrates. We want to learn which types of fuel you use during exercise, how your body’s metabolism changes during the time while you are exercising, and how this relates to your fitness and overall health.

Eligibility: Healthy men can participate in this study. Study participants must not be taking medication that affects metabolism or have any condition that would prevent completion of the maximal exercise test and subsequent exercise testing sessions. Healthy men participating in this study must be…

  • 18 – 30 years of age at the start of the study
  • Not too thin and not too fat (BMI 18.5-28 kg·m-2)
  • Free from pre-existing health conditions that limit physical activity
  • Free from orthopedic problems that limit physical activity
  • Non-smoker for at least 6 months
  • Weight stable for at least 6 months (gain/loss of up to 5 pounds acceptable)
  • Not a collegiate or professional athlete

Study protocol: This study includes up to 3 testing sessions. All testing will occur in the Michigan Clinical Research Unit Clinical Suite, located in the lower level of the Cardiovascular Center. All participants will complete the first testing session. Some participants will be invited to complete the second and third testing sessions. Participants may opt ‘in’ or ‘out’ of a variety of tests within this study.

All exercise will be completed on a stationary bicycle. You will wear a heart rate monitor around your chest so that we can continuously monitor heart rate. You will also wear a mouthpiece so we can measure oxygen consumption and carbon dioxide emission – this allows us to measure how hard you are working and which fuel source (i.e. fat, protein or carbohydrates) you are using during exercise.

Prior to every testing session, you must fast for 3 hours. This is to ensure that accurate energy expenditure results are obtained. Fasting means nothing to eat or drink other than water.

Session #1 will last up to 2 hours.

  • It includes one blood draw and one VO2 peak test. We will collect 10 mL (2 teaspoons) of blood.
  • You will exercise for ∼20 minutes.

Some but not all participants will be invited to session #2.

Session #2 will last up to 3 hours.

  • An intravenous catheter (IV) will be placed in a vein in your hand or forearm for blood sampling. This IV catheter is a very small flexible tube that remains in your vein during this session and eliminates the need to poke you with a needle every time we collect a blood sample. We will collect blood before, during and immediately after exercise. Metabolites in these samples will be measured and will allow us to determine fuel source with more detail – i.e. the type of amino acids, sugars and/or lipids your body uses during exercise. We will collect 60 mL (4 tablespoons) of blood during session #2.
  • You will exercise for only ∼40 minutes.
  • All muscle biopsies are optional and will not affect acceptance into this study. If you choose to participate in this portion of the study, we will remove a small muscle sample from your thigh before and again after exercise. This muscle biopsy procedure involves numbing a nickel-sized portion of the skin of your thigh with a local anesthetic, making a small incision (1/4 inch), and removing a small piece of muscle (approximately the size of 2-3 grains of rice). The incision will then be closed with a piece of sterile tape.

Some, but not all participants who complete session #2 will be invited to session #3.

Session #3 will last up to 3 hours. It will include all components of session #2 plus one additional component.

  • A second IV line will be placed in a vein in your hand or forearm for a tracer-labeled infusion. These “stable-isotopes” are non-radioactive and there are no known risks involved in infusing them. In fact, you already have these isotopes in your body. We are only very slightly increasing the amount of these isotopes. These isotopes are a way for us to track the movement of particular sugars, amino acids and fats into and out of the blood stream.
  • The infusion will begin before you exercise and will finish when you stop exercising. As in session #2, you will exercise for only ∼40 minutes.
  • We will collect 60mL (4 tablespoons) of blood during session #3.
  • Optional: We will collect one muscle biopsy before and one muscle biopsy after you exercise.

Total blood volume and biopsied samples: The blood volume collected in session #1 is 10mL (2 teaspoons). The blood volume collected in sessions #2 and #3 is 60mL (4 tablespoons)/session. Muscle biopsies are optional. If you elect to participate in muscle biopsies, we will perform two muscle biopsies during session #2 and up to two muscle biopsies during session #3. If you complete all sessions and all biopsies, we will collect 130mL of blood (about 9 tablespoons) and 4 muscle samples from you.

A portion of these samples may be stored for future analysis. The label on these stored samples will not have any personal identification and they will not be able to be linked to you.

How much of my time will be needed to take part in this study? This study includes up to 3 testing sessions. Session #1 will take up to 2 hours to complete, session #2 and session #3 will each take up to 3 hours to complete. You will exercise for ∼20 minutes during session #1 and ∼40 minutes during sessions #2 and #3. All three sessions will be completed within 1 year.

When will my participation in the study be over? This study will last up to 1 year and includes up to three testing sessions total. All participants will complete session #1. You may or may not be invited to complete sessions #2 and #3. Your participation will be over when you have completed all sessions to which you have been invited.

Compensation: You will be compensated $25 after completing testing session #1, $50 after completing session #2 and $75 after completing session #3. You will be compensated an extra $50 for each muscle biopsy we perform (all muscle biopsies optional).

Contact: To sign-up for this study, complete the screening questionnaire. If you are eligible to participate, we will contact you. If you have questions for us, contact us: INTMED-MMOC-PAL-RESEARCH@med.umich.edu (include FUEL in subject of email).