How many calories do you burn in an Ironman?

Putting in the effort that is required to complete a full Ironman is immense. It requires tons of energy to get you to that finish line. The three different elements ensure that you need to use all the muscles, organs and fibers of your body. But how many calories are actually being burned during an Ironman? 

The total amount of calories burned during an Ironman on average is between 7.000 and 10.000 calories. However it is dependent on a lot of factors, such as the course difficulty, the weather conditions, gender, intensity level, efficiency, body weight, metabolism, and others. Hence, the bandwidth can be stretched even more for some athletes in certain circumstances.

Given the fact that this amount of calories will be burned, how do you prepare for that? And can you compensate for those lost calories during the race? Read on to find the answers.

Calories burned by Josh and Jasmine

Let’s take two examples to make things more specific.

Example 1: Josh – male – 80 kg 

Josh is an average triathlete. He has a medium fitness level, which is substantiated by his 18% body fat percentage (<12% = high, 12 – 20% = medium, >20% = low). Josh is an age grouper that completed his first Ironman. Again, with all sorts of disclaimers in mind, here’s what his burned calories look like.

	Minutes	Hours	Total calories	Cal/min
Swim	78	1.30	721	9
Bike	360	6.00	4.827	13
Run	240	4.00	3.882	16
Total	678	11.30	9.430	N/A

Put all sports together and Josh just burned over 9.400 calories during the course of the race. You can see that the swim element burns the least cal/min and has the lowest total amount of calories. Whilst the bike session, due to its length, ensures that Josh burned the most calories but not the most cal/min. Running seems to have the most impact, looking at the cal/min.  

Example 2: Jasmine – female – 65 kg

Jasmine is a more advanced triathlete. She has a high fitness level, which is indicated by her 16% body fat percentage (females can add 6% to the upper guidelines). Jasmine is an experienced Ironman who completed 4 triathlons. Here’s what her burned calories look like.

	Minutes	Hours	Total calories	Cal/min
Swim	70	1.17	536	8
Bike	324	5.40	3.599	11
Run	216	3.60	2.895	13
Total	610	10.17	7.030	N/A

The total amount of burned calories for Jasmine was over 7.000. The same logic applies for Jasmine as well as for Josh with respect to cal/min vs total calories. There are different calculators that you can try yourself.

Notice the difference between the two triathletes: 9.400 vs. 7.000 calories burned. These are just two examples that I want to provide you with to make things explicit. Other athletes may burn over 10.000 calories at an aggressive pace over the course of the race. It’s all possible.

Check out these amazing triathlon movies and documentaries and Instagram accounts to get you even more in the Ironman mood!

How do you compensate for those burned calories?

How much you need to eat and drink during each event really depends on your body’s ability to process the calories and your ability to use stored fat as fuel.

In the example of Josh, he burns 9430 / 11.3 = 834 calories per hour. Now, you do not need to consume all these calories to keep your energy level up and running. A part will be covered by calories burned by the body’s fat. Plus, every person has glycogen storage – a buffer of calories – that will be used as well. Taking those two variables into consideration, Josh still requires around 400 calories per hour.

The same applies for Jasmine. She burns 7030 / 10.17 = 691 calories per hour. When deducting the calories burned by body’s fat and the glycogen storage, Jasmine still required around 300 calories per hour. 

A body can digest only a maximum number of calories per hour; this is not infinite. Roughly, you can take 300 – 400 calories per hour. So for both Josh and Jasmine this is within their range. 

Calories can be taken from drinks, gels, bars, fruits, what have you. During the swim section you will not take any drink of food, but during the bike and run there are lots of opportunities. A gel could contain up to 100 calories, so taking 2 or 3 of those per hour, with energy drinks and water, will get you there. But in the end it is all dependent on your metabolism. 

Just bear in mind to train with the supplements that you will use during race day. Do no experiment with new things!

How many calories do you burn in other types of sports?

To put the effort of an Ironman into perspective, let’s look at some other sports and the amount of calories burned. In this top 10 overview, the amount of calories per sport is calculated by the parameter of a person of 90 kg, who exercises fanatically for one hour.

10. Backpacking

Pack your bag and fill it with an extra pair of shoes and clothing. Because you need your backpack to be very heavy in order to burn up to 627 calories per hour.

9. Ice skating

Ice skating on an intensive level requires a lot from your legs and the core. One hour of intensive skating on the ice will burn 637 calories. 

8. Basketball

Basketball is physically and mentally tough and requires strategic thinking. Dribble, pass, dunk, block, push and pull. A fanatic basketball play of one hour will burn 728 calories.

7. Tennis

A doubles versus a single match differs quite a lot with respect to the required energy. But for a singles match of one hour, with kick serves, flat volleys, hard baseline tennis and short cross slices, you will burn 728 calories. 

6. Running (8 km/h)

The rhythmic movement of your arms and legs ensure that you will burn quite some calories. If you keep the speed at 8 km per hour, which is quite a low effort, you burn 755 calories.

If you want to be more efficient – hence use less calories – in the running section, you might be interested to read the blogs about stretching protocols, the interval runs and the long runs.

5. Walking the stairs

This is tough. An hour of walking up and down the stairs will fill your muscles with lactate. But if you are up for it, you will burn 819 calories in an hour. 

4. Swimming

This is not simply doing a breaststroke in the indoor pool, but some serious freestyle in the fast lane. With powerful strokes you go back and forth for one hour. This will burn 892 calories per hour. 

If you are in your preparation phase for an Ironman, here is when to start with your swim training as beginner.

3. Taekwondo

An incredibly intensive sport, maybe the most in this list. A Korean form of martial arts characterized by punching and kicking techniques, with emphasis on head-height kicks, spinning jump kicks, and fast kicking techniques. With this sport you burn 937 calories per hour. 

2. Jumping rope

Maybe an unexpected shared first place for jumping rope! It has become more popular these days and requires lots of energy from almost all muscle groups in the body. A perfect exercise to burn 1.074 calories per hour. 

1. Running (13 km/h)

Shared the stage with jumping rope is running, on a 13 km/h pace. Compared to the number 6 in the list, this is 5 km/h faster. If you manage to keep that tempo for one hour, you burn 1.074 calories.

When not taking all those calories into account, read here what is harder: a marathon or triathlon.

Final note

You cannot directly link this overview to the examples of Josh and Jasmine, as their weight and fitness level is different. However you are now able to put the required energy in a broader context. Overall you could say that two out of three of the Ironman disciplines (swim and run) rank high in the ‘calories burned list’. Taking into account that one needs to do that for not one but 10 or 12 hours, you can conclude that the Ironman asks something extraordinary from your body.

Finding time to train for an Ironman can be challenging. Read this article to get tips how to use your time more efficient.