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Category: Nutrition

Energy Availability

Posted on November 18th, 2016 by

We all have experienced once in a while a poor training run. Running through tiredness, suffering from low energy levels and after a few minutes into the run we would have wished to have opted rather for a rest day. For those of you preparing for a marathon and doing their long runs, you may have hit the wall and experienced what it means to run low on energy. You are wondering why this is happening to you. On other training runs, we feel great, firing on all cylinders and everything feels relaxed. Energy levels play a vital role and determine the quality of our training runs. In this week’s Hare Brains blog, we want to explore what drives our energy availability and highlight important considerations.

So far I have written a lot about the specifics of endurance training and provided relevant information for the winter training plan. The training schedule explains the types of runs, distances, duration, pace and intensity. When we put a training plan together, we assume, runners have infinite amounts of energy available. We are confident that we always manage to complete the running session as scheduled. Common belief is, for anything longer than 1 hour we don’t need to fuel. Hydration and nutrition are more an aftermath.

Nutrition for distance runners is highly relevant if we want to compete at our best. For a powerful aerobic engine to produce the maximum energy output, what goes into the engine, high-performance fuel is vital. When immersed in running, nutrition plays a second role. Without adequate fuelling, we cannot perform and sustain prolonged periods of training.

In the weight-sensitive sport of running, we are conscious about our physical appearance and weight. After all the hard training, we want to maintain an ideal weight and get anxious about putting on more weight. If we put too much emphasis on trying to control weight beyond healthy levels that it affects our eating patterns, then it can have a detrimental effect impacting performance.

A well-balanced diet is the foundation of healthy and smart training. However, those new to structured training face a problem regarding how much fuelling is required to sustain the training week, month and entire season. Important considerations, which need to be factored into the training regime.

Endurance runners often ask, what should I eat before, during and after a run? While the intent of this blog is not a discussion on the latest diet trends (high carb/low fat or high fat/low carb), we want to highlight the importance of managing energy availability (irrespective of a particular diet).

For the body to function, we need to meet the minimal energy requirements for its organs to work. If we do not do that, or if we try to fast, inner organs will not receive the minimum amount of energy, which can have severe health implications.

Energy Availability (EA)

Energy needs are highly individual. No two runners are the same. Energy requirements vary according to body size, the energy cost of training (volume, frequency, and intensity of workouts) and growth or changes in body physique. For example, a young athlete experiencing maximum growth spur requires different amounts of energy in comparison to a well-conditioned master runner. Those running 80 miles per week have a significantly higher energy demands compared to those training 40 miles per week.

The term ‘Energy Availability’ (EA) has been used by exercise physiologist to reflect the specifics demand of energy requirements for sport. When not taking part in sport, we expend less energy compared to anyone who takes up sports for a couple of hours per week. The term EA takes this into consideration. EA  refers to the amount of energy left over and available for your body’s functions after the energy expended for training is subtracted from the energy you take in from food.

A balanced EA is essential for cells to function, muscles to repair, maintain body temperature and keep the immune system intact. EA is a vital input to the body’s physiological systems.

Energy Availability (EA) is calculated based on energy intake (EI) minus exercise energy expenditure (EEE). As a guideline, healthy athletes have 45 kcal/kg FFM (Fat-free Mass). Maintaining a normal resting metabolic rate requires 30 kcals/kg FFM. EA lower than 30 kcal/kg FFM is considered alarming. Similar to a scale, EA illustrates a balance between EI and EEE. If EEE is very high and EI is low, then EA is out of balance and vice versa.

EA and energy balance are mixed and used interchangeably. However, both concepts are not related. Energy Balance (EB) consists of Energy Intake (EI) minus Total Energy Expenditure (TEE), i.e. beyond energy expenditure beyond exercise. EB is rather an output from the body’s physiological systems. It is less significant for athletes to maintain EB.

Important to keep in mind is that body weight is not an accurate reflection of energy availability. While body weight can be at a healthy level, EA can be out of balance. When the body is not functioning at full capacity, the body preserves weight and decreases the resting metabolic rate to maintain the body’s function.

What are the causes for low Energy Availability?

There are some reasons which can contribute to low energy availability. Low energy availability can be caused unintentional or intentional.

Unintentional, in the event an athlete starts to build up weekly mileage as part of a marathon preparation. When we double weekly mileage from 25 miles per week to 50 miles per week without adjusting energy intake, then EA is declining. The runner has a lack of awareness of their increased exercise energy expenditure, which results in weight loss and not eating enough.

Intentional, runners are trying to reduce their weight and reducing their energy intake too far. Reducing energy intake too far and too rapidly. This results in a slow metabolism and weight loss start to plateau. Additional reduction to unhealthy levels would be required to promote further weight loss, which total energy expenditure and performance in a negative manner.

Psychological reasons can cause Low energy availability. Eating disorders and disordered eating, which are present in athletics and many other endurance sports. In the event eating patterns are affected, runners should seek professional and specialist help.

Case Study 1 – Athlete, trains 3x – 4x / Week

Let’s look at an example of a typical club runner, training three to four times per week. A 50 kg athlete with 10% body fat running for up to 1 hour per day, would require a minimum energy intake 2250 kcal. The amount of body fat corresponds to 5kg (10%), which is subtracted from the bodyweight, resulting in 45 kg lean body mass (LBM). Applying the EA formula, energy availability would be 2250 kcal – 1000 kcal, 1250 kcal. A healthy individual requires 45 kcal per kg (lean) body weight, hence 28 kcal per kg lean body mass. In this case, the athlete is below a healthy level of 45 kcal/kg and low on energy availability. This means the athletes dietary energy intake is insufficient to support the energy expenditure required by the body to support healthy daily living after the cost of exercise has been taken into account.

If the runner were 10 kg more, with the same amount of body fat, the energy intake would be 3250 kcal, resulting in 42 kcal/kg LBM which is a healthy level of energy availability.

As distance runners, our energy demands are higher. We need to make sure we adjust our energy intake.

Case Study 2 – Ultra Runner

One of my athletes has completed the 84 mile Druids Challenge, a multi-stage race of 3 marathons on three consecutive days. On average, based on Fitbit data, the athletes Exercise Energy Expenditure (EEE) was 4500 kcal / day.

As an ultrarunner, running approx. 10 minutes per mile pace, energy is provided by approx. 50% carbohydrates/muscle glycogen and 50% body fat. Like for any marathon, it is important to load up carbohydrates before the race to ensure muscle glycogen stores are fully charged up.  After each marathon, the recovery process begins, followed by replenishing depleted muscle glycogen stores.

What would be the athlete’s Energy Availability (EA)? Let’s assume a 70kg ultra runner with 15% body fat (10.5 kg), equates to 59.5 kg lean body mass (LBM). As stated above EEE is 4500 kcal / day during the competition with the aim to maintain a healthy EA of 45 kcal / kg.

59.5 kg x 45 kcal/kg + 4,500 kcal = 7,177.5 kcal = EI

During a multi-stage ultra-event, energy intake of 7,177.5 kcal is required to maintain healthy levels of energy availability. A lot of food to take in to maintain a healthy EA. EI needs to be carefully dosed to avoid GI distress.

However, the EI contains all energy intake during the race too. Let’s assume our ultrarunner used energy gels during the race. For example, a Powerbar Performance Energy Gel provides 110 calories. Taking on 2 Energy Gels every 30 minutes, would provide 220 calories / hour (1,100 kcals during the race). We know from marathon training we can only consume a limited amount of carbohydrates within 1 hour. Approx. 20% of the Exercise Energy Expenditure / hour, 180 kcals / hour of carbohydrates, consumed through energy gels. Still, our ultrarunner needs to replenish a minimum of 6,000 kcals after the race.

If the athlete does not follow a strict fuelling protocol, it will be only a matter of time until muscle glycogen stores get depleted, forcing the runner to slow down and impacting the recovery process.

What effect does low Energy Availability have?

Chronic low energy Availability can have a severe health implications. In the past, chronic low energy availability was linked to the Female Athlete Triad. The Female Athlete Triad is concerned with the inter-dependency between energy availability, lack of menstrual cycle and bone mineral density. The triad moves along a spectrum from optimal health to pathology. However, the International Olympic Committee (IOC) has revised, updated and broadened the concept of the Female Athlete Triad and coined a new term ‘Relative Energy Deficiency in Sport’ (RED-S). RED-S refers to impaired physiological functioning caused by relative energy deficiency including, but not limited to metabolic rate, menstrual function, bone health, immunity, protein synthesis (muscle repair) and cardiovascular health. RED-S highlights the underpinning issue of the energy deficiency and put energy deficiency in the context of performance.

RED-S applies to men as well as women. RED-S describes a situation when athletes are not taking on enough energy for growth, repair and their training needs. However, RED-S equally applies to non-athletes too, everyday people not taking on enough energy.

Relative energy deficiency in sport affects almost all body systems. The immune system, menstrual cycle, bone density, metabolism cardiovascular, digestive system, etc. Psychologically, energy deficiency can impact psychological system in both ways, as a result of low energy or directly from eating disorders.

Despite the physiological and psychological body functions, RED-S impacts performance. Endurance levels drop, the risk of injuries (stress fractures), lack of response to training, anxiety, depression and lower muscle glycogen stores are performance related consequences of RED-S.

Managing Energy Availability Levels

Most of us have a packed day and a busy work / lifestyle. Balancing training and social life can be challenging. However, when you plan your training ahead you can prepare your energy intake.

The more we train, the more energy is needed. The same applies when the intensity of your training increases. Ensure energy intake aligns with training load and intensity. When training more intense, up your carbohydrate intake to ensure muscle glycogen levels are at full capacity. Timing is equally important. Always have a snack available for before and after a training session. Missing out on replenishing burnt calories slows down the recovery process.

Some run to work from time to time. Don’t skip breakfast, it’s the most important meal of the day and is part of a healthy diet. Aspire to a regular eating pattern, even though if work sometimes gets in the way.


Every runner, female and male, should be aware of the concept of Energy Availability (EA) and RED-S. To optimise performance, managing Energy Availability during periods of more frequent and intense training is important.

Endurance athletes can track their EA as part of their training and balance their food intake. Contrary, if things don’t go so well, revisiting the notion of Energy Availability can provide clues where your training has gone wrong.

Urban Bettag coaches for the Mornington Chasers and leads the development of their track training and mentors their junior coaches. He blogs and shares his wisdom about running on the Hare Brain Blog every Friday.