If you train and want to improve your performance, you must eat enough. But how do you know if you get enough energy into your system? The answer is to be aware of your energy availability - the new-comer within the tools of performance improvement.

Why energy balance is old-school for athletes?

You may have heard of energy balance that is commonly used for evaluating the “energy in” you get to cover the energy expended (“energy out”). It equals for equation “dietary energy intake kcal – total daily energy expenditure kcal”. Dietary energy intake means the energy consumed from food and drinks, whereas total daily energy expenditure is energy expended for movement and organ functions.
However, energy balance does not provide the best picture of energy requirements as it lacks information whether the body’s physiological systems are functioning in a healthy manner (Loucks et al. 2011). For example, if you do not eat enough, your resting energy expenditure decreases, which again results in decreased level of total daily energy expenditure as your body compensates inappropriate energy intake (metabolic adaptation). Energy balance is also rather challenging to estimate as many factors affect the daily energy expenditure.

Energy availability is the new black

Energy availability has recently gained popularity as an evaluation tool for the right level of athlete energy intake. It means the amount of energy after exercise left for resting energy expenditure, muscle damage repair, exercise adaptation (producing new muscle, nerve and bone tissue), immune system, and hormonal functions. Appropriate energy availability allows you to train, recover, improve performance, and stay healthy. (Ilander 2014)

Energy availability stands for the equation “(dietary energy intake kcal – energy expended in exercise kcal) / fat-free mass kg”. In contrast to energy balance, energy availability calculation requires information on exercise energy expenditure and fat-free mass (see example calculation).

Example calculation of energy availability:

Athletes should aim for energy availability above 40 kcal/kg, as it allows performance improvement, optimal performance and health (see table below). Energy availability at the level of 30-40 kcal/kg may be beneficial if the goal is to lose weight for a relatively short period of time. (Ilander 2014)

Levels for energy availability (modified according to Ilander 2014):

It is not recommended to drop energy availability below 30 kcal/kg, as it may increase injury risk (Ilander 2014). According to Loucks et al. (2011), energy availability may weaken due to various reasons:

• excessive training volume (in case the energy intake is not increased accordingly)
• eating disorder associated with clinical mental illness
• intention to rationally improve performance by reducing fat-mass and/or body size with mismanaged ways e.g. weight-loss, fasting, laxatives.

Inappropriate energy intake and energy availability weakens the recovery process from training, as glycogen stores do not refuel to the optimum level (Burke et al. 2011). In such case it is challenging to improve performance as the body’s physiological processes may be suppressed (Loucks et al. 2011).

How to ensure appropriate energy availability?

Earlier studies have indicated that increase in exercise volume did not change appetite: Two-day aerobic exercise (Douglas et al. 2014) did not change appetite in relation to carbohydrate and in fat intake, and 60-minute swimming session did not change carbohydrate, protein nor fat intake post-exercise (King et al. 2011). As a result, you may have inappropriate energy availability although you do not feel hungry. Therefore, after assessing energy availability, athletes should follow pre-designed meal plan rather than waiting for the feeling of hunger and eating until satiety (Loucks et al. 2011).

Dietary energy intake can be measured using food diaries (e.g. MyFitnessPal), energy expenditure with heart rate monitors, and fat-free mass with simple bioimpedance sensors (Ilander 2014). As you are not likely to eat the same amount of energy from day-to-day, it is recommended to record food diary for minimum of 7 days for energy availability calculations.

As a conclusion, energy availability is a convenient tool for making sure you offer your body the best conditions for performance improvement.

References

Burke L. Hawley J, Wong S, Jeukendrup A. 2011. Carbohydrates for training and competition. Journal of Sports Sciences 2011;9;17–27.

Douglas J, King J, McFarlane E, Baker L, Bradley C. et al. 2014. Appetite, appetite hormone and energy intake responses to two consecutive days of aerobic exercise in healthy young men. Appetite 2014;92;57–65.

Ilander O. 2014. Energia – syö riittävästi! In publication: Ilander O. (editor), Laaksonen M., Lindblad P. and Mursu J. Liikuntaravitsemus – tehoa, tuloksia ja terveyttä ruuasta. Saarijärvi. VK-Kustannus Oy 2014;19–38.

King J, Wasse L, Stensel D. 2011. The acute effects of swimming on appetite, food intake, and plasma acylated ghrelin. Journal of Obesity 2011;8.

Loucks A, Kiens B, Wright H. 2011. Energy availability in athletes. Journal of Sports Sciences 29: 28 Jul 2011.