How to calculate energy expenditure for Hyrox athletes

For athletes, understanding energy expenditure is about more than just calories in versus calories out — it’s about fueling performance, optimizing recovery, and maintaining a body that can train hard and compete even harder.

Energy management is performance management. Let’s explore how it works and how you can use it to your advantage.

What is energy expenditure?

Energy expenditure refers to the total amount of energy (calories) your body burns throughout the day to maintain basic functions, support training, and recover from it.For athletes, it’s the foundation of your performance equation — influencing how well you train, recover, and adapt.

Your total energy expenditure (TEE) is composed of three parts:

#1 Basal metabolic rate

This is the energy your body needs just to stay alive. This includes the most simple tasks such as breathing, circulating blood, repairing cells, and maintaining body temperature.

• Accounts for 60–70% of total daily energy expenditure.

  • This is a significant portion of your daily expenditure that you have very little control over.

• Higher muscle mass = higher BMR.

  • While this is true, the increase in BMR is negliable due to a 1kg increase in muscle mass will only increase BMR by around 13 kcals per day. Therefore, it may be worth looking at the other components of TEE to influence body composition changes.

#2 Thermic effect of food

This is the energy cost to digest, absorb and metabolise food.

• This only accounts for around 10% of TEE but it can be influenced by the foods you eat.

• Protein has the highest thermic cost at around 20-30% meaning up to a third of the calories ingested are used to process the food within the body.

• Carbohydrates and fats are significantly lower at 5-10% and 0-3% respectively.

#3 Physical Activity

Of all the components of total energy expenditure, Physical Activity is the most dynamic and the most within your control. For athletes, it’s also the one that fluctuates most dramatically from day to day — depending on training intensity, duration, type, and even recovery status.

Physical activity includes 2 key concepts

1. Exercise Activity Thermogenesis. This is the energy burned during deliberate, structured training (like workouts, practices, and competitions).

2. Non-Exercise Activity Thermogenesis. Also referred to as NEAT. This is the energy burned from all non-training movement: walking, fidgeting, stretching, doing chores, or standing between sessions.

Being able to understand how the intensity and time of a session will massively influence the required nutritional intake before and after training can massively impact the quality of the session and the recovery after the session.

How to measure your TEE?

While there are many ways to measure energy expenditure, there are a few that work best for athletes. If you'd like to know more about each one individually, check out this blog post.

The most effective way for athletes?

• To calculate BMR - A mix of predicitive equations and your wearable device would give you a good indication of where your BMR is.

• To calculate energy expenditure - Combine heart rate data from your sessions and your wearable device's output.

Is there a perfect way?

Without spending shed loads of money on direct or indirect caliometry it is unlikely that you will be able to know your EE down to the last calorie. However, these methods above will give you a good indication of the estimated expenditure daily and from each session, enabling you to tailer your pre and post workout nutrition to get the most from every session.

Conclusion: Energy expenditure

Understanding energy expenditure is essential for athletes to optimize performance, recovery, and long-term health. By tracking both training and daily activity, fueling appropriately, and adjusting for workload, athletes can ensure their bodies have the energy needed to perform at their best.