Energy systems: which one, for how long, and why

Three systems, and what each is for

The first system uses the small store of creatine phosphate already sitting in the muscle. It needs no oxygen, it is available instantly, and it is spent in about ten seconds. It is what a shot put, a lift or the first few strides of a sprint run on.

The second breaks down glucose without oxygen. It takes over as the first store runs down, it can hold up to roughly a minute or two of hard work, and its by-product is what makes the last part of a four hundred metre run feel the way it does.

The third uses oxygen and can run on carbohydrate and then on fat. It is slower to come up to speed and it lasts as long as the fuel and the oxygen do. Everything longer than a couple of minutes is mostly this one.

• Creatine phosphate - instant, about ten seconds, no oxygen.
• Anaerobic glycolysis - fast, up to a minute or two, no oxygen.
• Aerobic - slower to start, lasts, needs oxygen.
• Fuel matters: carbohydrate first, fat later, and only aerobically.

They overlap, they do not take turns

The commonest mistake in this topic is describing the systems as if a switch were thrown between them. All three contribute at once; what changes is which one is contributing most, and how that share moves as the effort goes on.

So the good answer says predominantly rather than only, and describes a change over time rather than a sequence of separate phases. In a game, the share moves back and forth many times: a sprint pulls the first two forward, the walk back lets the third one catch up and start restoring what was used.

That is also why the answer to a team sport question is not one system. A midfielder needs the aerobic system to get through eighty minutes and the anaerobic ones for every sprint inside it, and saying both, with what each is doing, is what the marks are for.

What recovery actually restores

Recovery is not one thing and the question usually means a specific part of it. The store in the first system comes back quickly - most of it within a couple of minutes - and it comes back aerobically, which is why an athlete keeps moving gently rather than stopping dead.

The by-products of the second system clear faster with light activity than with rest, which is the reason a cool-down is not a formality. Glycogen takes hours and needs food, and it is why what is eaten after a session is part of training rather than separate from it.

A question asking about recovery between efforts in a game wants the fast part. A question asking about recovery between sessions wants the slow part. They have different answers and reading which one is being asked is most of the mark.

Answering about a specific sport

When the question names a sport, the answer has to be about that sport. Name the movements, say roughly how long they last, and then say which system is doing most of the work during each, and how that shapes what training should look like.

The pattern that scores is: this is what the activity demands, this is which system supplies it, and therefore this is what a session should contain. A generic paragraph about the three systems that mentions the sport once in the first line is a definition wearing a costume.

Use the numbers. Ten seconds, a minute or two, and everything above that is a rough but real division, and using it shows that the table has become something you can reason with rather than something you memorised.

Training the system the sport uses

Training is specific. Long steady work improves the aerobic system and does very little for the first ten seconds of a sprint. Short maximal efforts with long rests train the first system, because the rest is what lets the store refill before the next effort.

Interval work sits between them and the detail decides which system it trains: the length of the effort, the length of the rest, and how many times. Two of those three change the answer, so a question giving you a session wants you to read all three before deciding.

And a training programme has to say what it is for. A programme described without the demands of the sport it is for is a list of activities, and the mark is for the connection rather than for the list.

Where it usually goes wrong

Five habits, all of them fixable without learning anything new.

• Describing the systems as taking turns rather than overlapping.
• Naming one system for a team sport that clearly uses all three.
• Answering about slow recovery when the question meant between efforts.
• Writing a general paragraph and mentioning the named sport once.
• Describing a training session without saying what it is for.

What to practise next

Take six sports and, for each, write two sentences: what the effort pattern is, and which system supplies most of it and when. Six of those takes fifteen minutes and it is the crossing from the table to the situation that the exam actually asks for.

Then take one training session you have done yourself and write what each part of it trains and why. A programme you can explain is a programme you can defend in an extended response.

Check yourself

Three questions on what is above. Have a go before you open them - reading an answer you have not tried to give is the version of this that does nothing.