Estimating energy needs and requirements for endurance training is not an exact science. Energy needs are determined by the Resting Metabolic Rate (RMR), Thermic Effect of Food (TEF), and Energy Expenditure for Activity (EEA). RMR accounts for 60-75% of a resting person’s daily energy needs. RMR is influenced by lean body mass, age, gender and level of conditioning. The body requires energy to extract nutrients from the food consumed. This is known as the TEF, which accounts for 10% of a person’s energy needs. The EEA is the most variable component to the energy balance equation, accounting for 30% of the total daily calories required. The EEA contribution, however, can go as high as 80% depending on duration and intensity of the training day.
The best indicators that suggest an athlete is meeting his calorie/ energy needs are stable body weight over time, sufficient energy for quality workouts at all training intensities, and adequate recovery for the next workout. Energy requirements can be estimated using total body weight. In using Table 6.1, a 150 pound male training for an olympic distance race that averages 18 hours of training per week would possibly need between 2,700 and 3,750 calories per day. It should be noted that an athlete’s energy or calorie needs, diet composition (amount of carbohydrate, protein and fat), and nutritional focus (race day fueling) may change during the course of the periodized training plan.