McArdle disease and carbohydrate ingestion before exercise: The effect of timing

The research involves bringing greater clarity to the highly contentious McArdle disease (MD) clinical practice guidelines of consuming sucrose before exercise, The trials aim to determine conditions under which the ingestion of sucrose prior to exercise would be of most benefit to an individual with MD Prior to experimental testing each participant will undertake exercise testing to determine maximal continuous exercise capacity. Conventional methods (VO2max testing) are not appropriate for measurement of aerobic exercise capacity in individuals with MD due to substrate availability being the limiting factor during exercise and not O2 consumption. As a result, a maximum steady state power output (PPO) will be used to determine exercising capacities. . The repeated measures experimental trials will consist of 3 separate sessions (one experimental trial per session) each separated by a minimum of 48 hours. For each trial, participants will arrive at the laboratory at ~7.30 am in fasted state. Upon arrival, a cannula will be placed into the antecubital vein and a resting blood sample (6 mL) will be drawn. In a randomised, crossover design participants will be allocated one of 3 experimental protocols for each session: 1) Sucrose 25 mins before exercise (SUC25) 2) Sucrose 5 mins before exercise (SUC5) 3) A placebo group (PLA) Once the participant has been assigned to an experimental protocol, they will be fitted with a heart rate monitor and will consume the designated beverage of the condition (sucrose or placebo). Sucrose protocols will consume a beverage containing 37 g of sucrose with 250 mL of water. Fasted protocols will consume 250 mL of water artificially sweetened zero-carbohydrate substitute to blind participants for conditions. 5-minutes after the consumption of the designated beverage, participants undertaking the SUC5 trial will then be fitted with a mouthpiece to collect continuous expired breath, a second blood sample will be taken, and participants will begin cycling at a steady state at 60% of their previously determined PPO. 25-minutes after the consumption of the designated beverage, participants undertaking the SUC25 trial will then be fitted with a mouthpiece to collect continuous expired breath, a second blood sample will be taken, and participants will begin cycling at a steady state at 60% of their previously determined PPO. Blood samples will be taken at 0,5, 10, 15, and 20 minutes of each exercise trial. Expired gas, and heart rate will be continually collected throughout the 20 minute trials. Rating of perceived exertion (RPE) will be collect at every 1 minute interval using a 20 point Borg scale. The trials will take place under the guidance and supervisor of highly qualified and experienced Exercise Scientists and Exercise Physiologists.