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What Is Energy?

Energy is fundamental to live, train and perform. Energy is the currency of life. Understanding what energy is helps us to better listen to our body’s energy needs … and ultimately perform better.

Pictures this: It is the dawn of a new day. Ashleigh is feeling the effects of yesterday’s training and knows that today is her chance to get better. She is tired, but still wants to give her all to this new day.  Ashleigh needs energy, but what is energy and where does it come from?

Track cycling athlete Alysha Keith during a casual training ride in the hills above Cambridge, New Zealand. Photo: Derek Morrison

Energy is fundamental to an athlete’s training and performance. Think about energy as the currency our body uses to get things done. Unlike a car that we drive and then turn off, our body never turns off. Even when you are not exercising your body works all day long. And all night long.

And there is more than just that going on in your body, way more. Even while you sleep. All of that requires energy.

The Work Of Living

Your heart beats, your brain thinks, your kidneys filter your blood. Your liver sorts through the food you ate and sends nutrients out to your body. Your bones and muscles grow and repair. Your immune system patrols, finding where it needs to work.

In fact, all that living: eating, sleeping, studying, working and keeping your organs and body ticking along nicely; makes up 70-85 percent of your daily energy needs. Any exercise you do on top of that can make up an extra 15-30 percent of your daily energy needs (depending on how much exercise you do, of course).

Food Energy

Laughing makes us feel good. It gives us energy. But really, all the energy we were talking about just now, needs to come from your food. We describe food energy as either calories or kilojoules, depending on where you live. It is very easy, in the Western world especially, to eat more than we need for the amount of work our body does.

When we eat too much, we have a very efficient way of storing the extra energy – as body fat. Historically, this has been really useful, ensuring the survival of the human race through long periods without food – like seasonal changes in food availability (think of remote plateaus covered in ice and snow for half the year). Food supplies run low for lots of reasons, like during a drought, or a flood, or when our ancestors would move from location to location to search for new places to live, probably to secure a better food supply.

Energy In The Modern Environment

These days, food can be everywhere around us. Cheap, calorie-dense food, too. Often with very few other nutrients alongside, if any. It is a far cry from our hunter-gatherer early human days.

Athlete food table at the Singapore National Age Group Championships at the OCBC Aquatic Centre, Singapore. Photo: Derek Morrison

Now, we can eat a lot of energy really easily and it won’t cost us much in either time, effort or money. Compared to our ancestors, we move our bodies less and less. We drive instead of walk, we push buttons instead of doing physical household chores like laundry and dish-washing and we often sit all day at work.

Thankfully, we are speaking to an active audience right now. When you exercise, you are boosting the amount of work you do. And it is good for you.

Energy For Growth

If Ashleigh is still growing, she needs even more energy. Growing is a demanding business, just like training. So if you are still growing, you are in the double-up sweet spot of needing lots of energy to grow healthy, strong bodies. Enjoy it while you can.

You don’t just need calories to grow. You have a whole body to grow, there is a lot going on in there. You need many other nutrients to grow your bones, your muscles, your brain, your liver, your blood vessels and so it goes on: all of your body.


Energy is the currency our body needs to do the work of living, alongside the demands of physical activity and growth. Keeping ourselves alive requires more energy than you might think and physical activity means we need to eat more energy from food. If you are still growing, you need even more again. Eating foods containing good quality carbohydrates, protein and fat alongside plentiful vitamins and minerals is the best way to supply your body with the kind of energy it needs to live and perform well.

Check out our other videos and articles to help you understand more about what nutrients you need.

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