Fuel Selection During Eccentric Cycling With Glucose Ingestion

Two ingestion modalities will be attributed (participant is blinded) in random order: a placebo and a glucose solution. The placebo contains water and a non-caloric sweetener (stevia) in order to reproduce the taste of the glucose solution. The glucose solution contains 6% glucose per volume, labelled with 13C. Both solutions will be administered in 8 doses: a bolus (333 mL) at rest, 30 minutes before the start of exercise, 167 mL immediately before exercise, 167 mL every 15 minutes during arm cranking, 125 mL immediately before concentric or eccentric pedalling and at 15 and 25 minutes of this last exercise period. In total, 1250 mL of solution will be administered during the experimental protocol.

The participants will perform 45 minutes of arm cranking on a specialized ergometer at a power output corresponding to 30% of their concentric cycling VO2max, previously measured.

Subjects will be asked, twice, to provide a forced expiration into a 10 mL plastic tube in order to collect a sample expired gases. This procedure will be done immediately before blood sampling and ingestion of the solution.

A mouthpiece and nose plug will be placed on the subject and expired gases will be analyzed by a metabolic cart during 3 minutes. This procedure will be done immediately before expired gas collection, blood sampling and ingestion of the solution.

A catheter will be inserted in an antecubital vein and a saline solution will be continuously perfused to maintain vein open. 10 mL of blood will be collected immediately before ingesting the solution for a total of 80 mL.

Maximal voluntary bilateral knee extensions (3 trials of 3-4 seconds each) will be performed on a chair equipped with force sensors to measure peak force production. These measurements will be done before the first ingestion, immediately before exercise, during the transition between arm cranking and concentric or eccentric cycling, and at the end of the exercise protocol.

Surface electrodes will be placed on the biceps and quadriceps to measure EMG throughout the exercise protocol.

Wireless sensors will be placed on the skin of the arm, chest, back, abdomen, thigh and calf using adhesive tape. A wireless thermometric pill will be ingested the morning of the experiment. These will allow the measurement of skin and central temperatures throughout the exercise protocol.

100 points scales (CR100) will be used to measure perceived exertion and pain perception immediately before ingesting the gas sampling. At the same time, affective responses will be assessed using the "Feeling scale".

Sweat production and sampling will be performed by measuring body weight before and after exercise, after voiding the bladder. Mass loss through the urine and gases will be accounted for in order to compute sweat production. A sweat sample will be collected using a cotton gauze placed into a plastic collector affixed in the upper back of the participants. A urine sample will be taken from the urine collected at the end of the exercise period. Urine and sweat volumes along with respective urea concentrations will be used to compute protein oxidation during exercise.