The peri-exercise period (that is; pre, intra and post exercise) is a crucial time for an athlete to promote optimal performance and recovery using dietary means. Exercise is strenuous and, depending on the duration, intensity and environment of the activity, can result in; reductions and or depletion of existing glycogen stores, increased protein oxidation, muscular breakdown, reduction in circulating electrolyte levels and reduction in hydration levels. All these associated factors, if not addressed through adequate dietary intake, can severely impede performance and recovery, if not leading to reductions in performance and recovery in subsequent bouts of exercise (be they the same day or in the days following). Therefore, the goal of dietary intake around exercise should be;
· To have a glycogen sparing effect and or restore glycogen stores
· Reduce protein catabolism
· Increase muscle protein synthesis
· Restore any loss in electrolyte levels
· Optimize hydration levels and ultimately avoid dehydration
Intra-workout nutrition should be focused on two key aspects; hydration levels and provision of glycogen sparing, high glycaemic carbohydrate. Concentrating first on hydration, recommendations for athletes for water intake consist of consumption of 250mls of water every 15 minutes of exercise. If this can be performed evenly throughout the 15-minute period it would obviously be more ideal for the performer but this isn’t always practical. Using half time and or any other stoppages would be an ideal time to “catch up” on the recommend amount of water consumption throughout training (if the recommendation of consuming 250mls every 15 minutes is not entirely feasible).
Electrolytes are also important to consider. As we train we sweat. This is to reduce core body temperature and obviously leads to loss of water. However, we also lose electrolytes in our sweat as well. The electrolytes are calcium, potassium and sodium and consumption of these should not be isolated to just the few hours surrounding and involving exercise but across the entire day. Reduced electrolyte levels can manifest in; impaired cognitive function, poorer decision making, reduced accuracy, reduction in muscle power/strength, increased muscular fatigue and increased risk of cramping. If dietary intake of electrolytes is adequate then further supplementation is not required (which is the case for most athletes), however additional supplementation would propose no negative consequences and therefore would be something I’d advise most athletes to consider taking with water during exercise (especially those in long duration, endurance based activities and or those exercising in warm to extreme heat climates).
Carbohydrate intake during exercise can be a useful tool to reduce the usage of pre-existing carbohydrate stores and maintain performance. We are aiming to consume high glycaemic/ simple forms of carbohydrate during long duration, intermittent and or low intensity exercise. When ingesting these it’s beneficial and useful to be aware of the oxidative limits of our body and how, if we over consume carbohydrate during training, this can lead to abdominal pain and discomfort (which can detriment performance). Our bodies are capable of oxidizing (which is essentially making use of/metabolizing) approximately 60g of carbohydrate an hour. This is due to the limitations of our carbohydrate transporters within the intestine and amounts over 60g may over saturate them (leading to the abdominal pain/discomfort I mentioned). However, if we use multiple forms of simple carbohydrate e.g. glucose, fructose etc. our oxidative capacity can increase as our body utilizes different transporters for different forms of carbohydrate meaning there is a decreased likelihood of us running into an issue with carbohydrate transporter over saturation.
For high intensity work, depletion of glycogen stores may not be as likely (however this is highly dependent on the actual duration and type of activity performed) so carbohydrate supplementation during exercise may not be as beneficial. Although there has been some evidence to support intra-workout carbohydrate benefiting high intensity work performance this may be due to other mechanisms outside of sparing glycogen. This is evident from studies that have evaluated mouth rinsing with carbohydrate and or the use of zero calorie sweeteners and found performance benefits for high intensity work. These studies suggest that it is not in-fact the carbohydrate itself but rather the “sweet” sensation of having the carbohydrate in the mouth which may stimulate certain regions of the brain related to reward and motor control (and subsequently improve performance).