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During Exercise Nutrition-Make it or Break it-


When it comes to endurance sports such as running, cycling, and triathlon disciplines, even in the setting of adequate preparation and training, inappropriate nutrition and hydration can affect performance and prevent athletes from reaching their goals during competition.

As stated by Burke et al. (2019), fluid losses >2% of body weight has been associated with perceived exercise fatigue and reduction in performance, becoming even more notorious in warm-hot environments making hydration an essential part of training and competition. Now, when athletes sweat, not only water is lost but also electrolytes, therefore replacement of these electrolytes becomes also important.


Fluid and Sodium


Ingestion of sodium during exercise promotes the perception of thirst and greater voluntary fluid consumption as well as greater plasma volume retention, reducing urine output. In summary, sodium intake will help athletes retain more fluid, decreasing the risk of dehydration when comparing to only drinking water. (McCubbin et. al., 2018). Recommendations for fluid intake vary depending on the duration of the training or competition event, and the environmental temperature however ranges from400-800mL/hour. Sodium losses vary among athletes based on their sweat rate, as well as event duration and environmental temperature but recommendations for sodium intake range form 300-600 mg/hour.


Carbohydrates


Now, let’s focus on carbohydrate intake. Recommendations for carbohydrate intake will vary depending on the sport type, duration of the event and intensity. Usually sports lasting below 30 minutes will not required exogenous carbohydrate sources, while sport events or training sessions lasting above 2-3 hours will require carbohydrate intake during exercise to maintain euglycemia or normal blood glucose levels and performance. Recommendations are for consumption of 30-60 gram/hour of carbohydrate in events lasting longer than 2-3 hours, up to 90 grams/hour in events or training sessions lasting longer (Jeukendrup, 2011).

Now, there is an important fact to point out. Carbohydrate oxidation is limited to approximately 1.1gram/minute when a single source of carbohydrate is provided (example: glucose) what equals to 66 grams/hour. Now in events lasting longer than 2-3 hours, providing a sole source of carbohydrate might not cover the athletes needs to maintain adequate levels of blood glucose and affect performance. The study conducted by Wallis et. al. (2005) concluded that when more than one source of carbohydrate was provided in a mixture (example glucose and fructose), oxidation rates increased to 1.5g/min or 90g/hour when about 108g/hour where consumed as glucose and fructose utilized different transporters for intestinal absorption. Moreover, the mixture of maltodextrin and fructose offered the advantage of better gastrointestinal tolerance as maltodextrin is neutral in taste and has a lower osmolality when compared to free glucose (Vitale & Getzin, 2019).


So what should I eat during exercise?


In summary, aim for sports drinks/powders that offer this combination of maltodextrin and fructose that will facilitate utilization of carbohydrate sources even when consuming up to 90g/hour in long lasting exercise training sessions and events. Recommendations for mixing it are ½ scoop or 1 scoop to 500mL making it a 4% or 8% carbohydrate solution respectively, and providing between 20-40g of carbohydrates per 500mL. Therefore intake of at least 1 L/hour will be recommended when no other source of external carbohydrate is provided.

Of note, general guidelines might vary among different sports, duration, intensity and athlete needs. Working with a sports dietitian to meet individual needs it is recommended.


References

Burke, L., Castell, L., Casa, D., Close, G.;,Costa, R., Deshbrow.,…Stellingwerff, T. (2019). International Association of Athletics Federation Consensus Statement 2019: nutrition for athletics. International Journal of Sport Nutrition and Exercise Metabolism, 29, 73-84.

Jeukendrup, A. (2011). Nutrition for endurance sports: marathon, triathlon, and road cycling. Journal of Sports Science, 29: sup1, S:91-S:99.

McCubbin, A. and Costa, R. (2018). Impact of sodium ingestion during exercise on endurance performance: a systematic review. International Journal of Sports Science, 8 (3): 97-107.

Vitale, K. and Getzin, A. (2019). Nutrition and supplement update for the endurance athlete: review and recommendations. Nutrients, 11 (6), 1289.

Wallis, G., Rowlands, D., Shaw, C., Jentjens, R., and Jeukendrup, A. (2005). Oxidtion of combined ingestion of maltodextrins and fructose during exercise. Medicine and Science in Sports and Exercise, 37 (3): 426-432.





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