The Intensity/Duration Curve – or “How come I walk for hours every day, but still get knackered climbing the stairs?”

Do you recognise the following:

“I think I’m reasonably fit.  I do a lot of walking (dozens of miles a every week), but I get so out of breath when I climb the stairs/run for a bus/play with the kids.  What is wrong with me?”

The Intensity/Duration Curve

The Intensity/Duration Curve

I recognise it.  Every single week someone comes up to me and asks me some version of this question, so here is the answer.

It is all to do with the Intensity/Duration Curve.  First of all, here are a couple of definitions:

  • Intensity:  The amount of work (exercise) done in a given unit of time. 
  • Duration:  How long it takes to do the work (exercise).

The graph shows how as the intensity of the work decreases, the duration of it can increase (point B or “Low Intensity” on the graph).  Or put another way, as the duration decreases, the intensity can increase (point A or “High Intensity” on the graph).

You can see this easily in the real world.  How long you can walk/jog is measured in hours, how long anyone can sprint flat-out is measured in only seconds.  Of course, the world is not simply black and white.  We are not restricted to either A or B, but we can do anything and everything in between.  And different things in life/training will naturally fall at different points on the curve.

Examples of A include:  100m sprint, high jump, long jump, throwing the javelin, running up a flight of stairs, running up a hill, punching a bag fast and hard, jumping.  These are all things that are explosive, fast or need a blast of full effort all at once.

Examples of B include:  marathon, walking, easy swimming, easy bike riding, basic gardening.  These are all things that are “slow burning”, still need effort, but you need to “pace” yourself.

Most of us spend our lives at the “B” end of the curve.  We try to make things as easy as possible in our lives (quite understandable).  But following the very basic principle of

“We get better at what we do”

we get relatively good at doing “easy” things for a “long time”, but get relatively bad at doing “hard” things “quickly”.  In other words, we get better at “B” and worse at “A”.  And when life forces us to do something intense (eg running for the bus/ambulance/bar etc), we are totally unprepared and find it a real struggle.

Now I am certainly not saying that high/low intensity training is better/worse than the other.  But they are different and if you are interested in good, solid all round general health and fitness (as hopefully you all are), you should be able to manage both.  And restricting yourself to just one end of the curve (usually the “B” end) will leave your shortcomings very exposed at the worst time.

So if you want to be able to handle “climbing the stairs” or any such higher intensity things like that, you need to make sure you are doing some higher intensity training.  The simple way of doing this is when you review your training, don’t progress by increasing the time/repetitions etc.  Progress by increasing the speed/weight etc.

As always, if you are interested in improving your health, fitness or training, or finding out where you are and where you should be training on the curve, contact me by clicking here.

I hope I have explained this curve well enough, because I will refer back to it in the future.  If you are scratching your head, puzzled at what I have written, please leave a question in the comments below.  And if you know anyone who could benefit from this, please “share” it with your friends.  I need all the help I can get spreading the word!