Maxwell's Marathon Training: Nutrition
The first step in calculating nutrition needs is to establish the number of calories needed on a daily basis for the body to perform optimally. This involves determining the Basal Metabolic Rate, which is the amount of energy in the form of food calories (kcal’s) that is required to meet your daily needs and then also accounting for my additional calorific requirements based on my training volume. I calculated my BMR at approximately 1’866 calories per day, which increased to 3’394 on most days when I factored in my activity level and increased to almost 5’000 calories on my long run days.
For endurance athletes, general recommendations for macronutrient intake revolve around a distribution of 60/20/20. This means you get 60 percent of your daily calories from carbohydrate and 20 percent each from fat and protein. Depending on training volume, carbohydrate needs will vary from 5 to 10 grams per kilogram of body weight per day, with protein needs also varying between 1.0 – 1.5 grams per kilogram of bodyweight per day. Dietary fat needs are less sensitive to fluctuations in training volume and will make up the remainder of your daily energy needs once your carbohydrates and protein needs have been determined.
Prolonged exercise requires sustained energy provision to maintain muscle contraction and is accomplished through the continual production of ATP (energy). Glycogen is the body’s storage form of carbohydrates and is found in the liver and muscles. It is readily converted to glucose to be used as an immediate energy source, especially during vigorous or continuous exercise, such as a marathon. It is important to begin to replenish the body’s glycogen stores immediately after exercise, to facilitate optimal recovery. The maximum window for glycogen replacement exists for approximately two hours post exercise, but it potentially take between 22 hours to four days after maximal efforts to fully replenish glycogen stores.
Electrolytes are chemicals that form electrically charged particles (ions) in body fluids. These ions carry the electrical energy necessary for many functions, including muscle contractions and transmission of nerve impulses. Many bodily functions depend on electrolytes, with optimal performance requiring an adequate supply of these important nutrients, with depletion leading to symptoms such as muscle cramping. When running we lose these through sweating so it is important to replenish them through hydration. On longer runs I take on electrolytes which are added to water, enabling me to maintain optimal electrolyte levels.