Energy Availability
What is Energy Availability?
In sport science, energy availability refers to whether or not you have adequate energy to support exercise but also normal physiological function.
If you subtract the calories you burn while training from your caloric intake, you're left with a certain amount of calories. That's your energy availability.
If energy availability is too low, you will not have adequate energy to support important physiological function, like metabolic and reproductive function.
This is often the case for lean individuals in a caloric deficit.
Relative Energy Deficiency
In a caloric deficit, a lean individual will often be in a state of low energy availability. However, this can occur at energy balance as well.
Even if you don’t expend a lot of calories in training, if you keep your energy intake low enough to maintain a leaner physique than your body wants, there can be health and performance consequences.
The state of exhibiting the signs of low energy availability while being at energy balance is known as relative energy deficiency.
Athletes who remain in a state of low energy availability can experience negative effects on:
- Performance
- Endocryne system
- Cardiovascular system
- Immune system
- Metabolic system
- Reproductive system
- Gastrointestinal system
- Body image
Calculating Energy Availability
Energy availability is calculated by dividing the amount of calories left over from training by lean body mass.
For example, let's consider a 10% body fat, 100 kg (220 lbs) male athlete, consuming 3000 kcal per day and expending 400 kcal on average in training.
| Body Weight | Body Fat | Daily calories | Training calories |
|---|---|---|---|
| 100 kg | 10% | 3000 kcal | 400 kcal |
In this case, lean body mass is 90 kg (198 lbs) and leftover calories are 2600 kcal.
| Lean Body Mass | Leftover Calories |
|---|---|
| 90 kg | 2600 kcal |
Dividing 2600 kcal by 90 kg we get an energy availability of 28.9 kcal/kg, or 13.1 kcal/lb.
Energy Availability Thresholds
When energy availability drops below a certain point, signs and symptoms of metabolic and reproductive downregulation can occur.
For many women, symptoms of low energy availability may occur within the range of 30-45 kcal/kg. In men, the threshold seems to be closer to 20-25 kcal/kg.
| Gender | Energy Availability Threshold |
|---|---|
| Female | 30-45 kcal/kg |
| Male | 20-25 kcal/kg |
Being aware of these thresholds is important. However, it's appropriate to assess not only the mathematical relationship, but also the signs and symptoms associated with low energy availability.
Symptoms of Low Energy Availability
Common symptoms of low energy availability include:
- Persistent food focus
- More frequent illness
- Poorer mood state
- Inability to increase performance
- Loss of libido
- Loss of menses or an irregular menstrual cycle
If restricting calories in order to maintain a certain level of body weight or body fat results in one or more of these symptoms, it might be appropriate to increase calories and maintain a higher level of body weight or body fat.
Conclusions
Bodybuilders and physique competitors often seek to maintain a certain look not only during competitions, but all year round.
However, if you lower your calories to maintain a leaner physique than your body wants, there can be health and performance consequences.
To keep fitness training healthy, productive and sustainable, it's probably a good idea to try to stay above 30 kcal/kg/LBM in women and 25 kcal/kg/LBM in men, but also pay close attention to signs of symptoms of low energy availability.