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
The 24 hours leading up to exercise/activity/sport is arguably equally as important as the time proceeding exercise/activity/sport. It is during this period that we can use our diet to promote an optimal state of glycogen storage prior to activity. The use of a high carbohydrate diet (which the literature recommends is between 7 to 10g/kg of bodyweight - however we like to calculate carbohydrate intake once protein and fat has been calculated as it is then relative to total calorie intake), has been shown to promote elevated levels of muscle glycogen which have translated into performance benefits amongst athletic populations.
As we get closer to exercise we can start to manipulate intake to address the other factors. For example, a meal containing protein and carbohydrate (25 – 40g of protein and between 25 – 100g of carbohydrate depending on time between meal and beginning of exercise) is heavily advised as this can not only provide an alternative fuel source (predominantly referring to the carbohydrate) to our stored glycogen and provide a “sparing” effect but it can also provide amino acids which will aid in combating protein catabolism whilst increasing protein synthesis. In times of lack of carbohydrate availability or prolonged deprivation these amino acids (as well as other substrates - amino acids tend to be the last gasp option as they are difficult for the body to convert to be readily available for energy production) can even be converted and used as an alternative energy source.
The form of carbohydrate, either high glycaemic or low glycaemic, is also an important consideration and is highly dependent on when the meal is consumed around exercise. For example, a high glycaemic carbohydrate source would be typically consumed within 60 minutes leading up to exercise and would typically range between 30 – 60g for a meal. A low glycaemic carbohydrate source would be more advised for any time beyond 60 minutes leading up to exercise and would be highly personalized (dependent on total calorie intake based on goals, lifestyle etc.) A serving of >60g would be my advice although, like I said, it is highly personalized. It should be noted that the closer to a training session you are the more you should focus on consuming carbohydrate from high glycaemic sources (typically within <30 mins until activity commences) to help avoid any digestion related discomfort.
Hydrating for exercise
Adequate hydration is critical for optimizing performance and recovery. As little as a 1% loss in body weight as a result of water loss can lead to significant performance detriment. Athlete’s should aim to consume approx. 500ml – 1litre of water in the 60 minutes leading up to exercise. Reaching the upper limits of this recommendation (1 litre) is only really required if the athlete has urinated once or more in the hour leading up and or they’re performing in a hot climate (>25 degrees).