We all know it's harder running uphill than on the flat. Obviously, running uphill you have to lift your body mass - even just a little bit - during each stride. This certainly requires extra energy. But how much? Can we measure the difference in energy required running uphill compared to running on the flat?
We can, and using my favourite 1km sprint as a test-case, we can quantify the difference.
Ever since the motorway run I’ve been obsessed with running 1km as fast as I can. I have a goal of bringing it down to 3 minutes flat, and figure that if I do the distance a few times every week it will happen.
Funnily enough my record remains 3 min15 secs – my time from the very first run and a time I have recorded twice since. So no progress – yet.
I have a good excuse this week though: I was in Melbourne last week and my morning runs there were on a 1km route that was slightly uphill. So surely running uphill would have caused my slower time? I would like to think so.
The best time I set on that route was 3:21 – a full 6 seconds off my record. So the question is: is it fair to say the uphill slope made me 6 seconds slower? Or was I just running slower because I was up late exploring the city each night? Today, I hope to understand exactly the effect running uphill has on energy required and therefore the speed of running.
Whenever I visit a new town one of the first things I do now is establish my 1km running route. In Melbourne, I chose a route just east of the CBD that began next to Rod Laver Arena (where Australian Open tennis plays) and finished at Flinders St. It’s hard to know the exact grade of the road, but I do know it sloped upwards gradually for the most part. Nice part of town, and a cool view of the city to look at along the way (it helps when you start hitting the wall).
That's the MCG bottom right; CBD top left. Red line is 1km.
My times for my three runs each morning were 3:22, 3:22 and 3:21. So what influence did the uphill slope likely have on these times?
There is a simple formula that a lot of treadmills and exercise calculators use to work out the calorific expenditure when running uphill compared to flat running (calorific expenditure – calories burned during exercise – is a fairly good indication of energy required):
Calories at %incline = (Calories at flat) x (1+ %incline)
So if I burn 1000 calories running for 1 minute on the flat, running for 1 minute (at the same speed) at 5% gradient I’ll burn 1000 x (1+0.05) = 1050 calories.
That’s simple enough. But intuitively it’s going to be wrong for steep gradients.
If we take a steep slope, say 20%, this formula says that you’ll burn only 20% more calories running up that slope at the same speed as you would running on the flat. Now running at a decent speed on a 20% slope is very difficult and it’s unlikely that you could maintain a speed the same as running on the flat for even a few minutes. You’ll burn out. It’s requires too much energy – it’s way more than a 20% increase in energy required.
Steep slopes take a lot out of you
The above linear equation only takes into account the effect of gravity when running uphill (having to raise your body vertically as you go up the slope).
But what about the increase in bodily effort that you need to apply? What needs to be considered is that when running uphill there is an increased demand on your muscles, and that your muscles are used in a different way. And this demand does not increase in a linear way as incline increases from flat to steep.
A 1997 study looked exactly at the differences in muscle activation and anaerobic capacity between uphill running and flat running (Sloniger, Mark A., Kirk J. Cureton, Barry M. Prior, and Ellen M. Evans. Anaerobic capacity and muscle activation during horizontal and uphill running. J. Appl. Physiol. 83(1): 262-269, 1997).
The tests basically measured:
Muscle activation: how much of your total leg muscle mass is used when you run uphill compared to flat.
Anaerobic capacity: the peak oxygen deficit you get in your muscles (an indication of how hard they are working). Oxygen consumption is a very good indicator of how hard you are working, and how many calories you are burning.
Results were measured for 12 subjects treadmill running at 0% and 10% grade.
The peak oxygen deficit determined for uphill running was 21% greater than flat running [2.96 litres compared to 2.45 litres).
The percentage of muscle volume activated for uphill running was 9% greater than flat running [73.1% compared to 67%]
Uphill running engages more of your muscles; quadraceps become more important.
We can conclude from this study that uphill running uses more of your total muscle mass, and in turn gives you greater overall oxygen deficit when running hard and exhausting the muscles. You would certainly feel 21% increase in oxygen deficit. You would become out of breath faster and then getting any oxygen in to working muscles would be more difficult. The inability to get oxygen into working muscles inhibits performance and makes it hard to run fast.
Considering a correlation between oxygen consumption and calorific expenditure, we could say that the calories burned as grade went from 0% to 10% increases by 21% also. Our initial linear formula predicts that calories burned would increase by 10% as the grade went from 0% to 10%. This suggests the linear formula becomes inaccurate by the time the grade reaches 10%.
What happens as the incline gets steeper?
A study by Minetti et al (J. Applied Physiol., 2002 Sep;93(3):1039-46) looked at adults running on a treadmill placed at varying extreme inclines. After running the subjects had blood draws done to look at oxygen consumption to determine number of calories burned.
I’ll spare you the full details (the studies got pretty complex). The main result we are interested in is this:
The calories burned as grade went from 0% to 20% doubled(200%). Now this is quite a steep gradient, but that is a very large increase in energy used. Again, to compare, our initial linear formula predicts that calories burned would increase by a mere 20% as the grade went from 0% to 20%.
When it's this steep you really notice the extra oxygen required to move
So it would seem that our initial linear formula underestimates by quite a bit the increased effort required when running uphill.
What becomes important is the increased volume of muscle that you have to use running uphill. As a hill gets steeper, you recruit more and more muscle to raise your body against gravity. Using more muscle means a greater oxygen demand – and to put it simply – makes it harder to breath and harder to run fast (and of course, it burns up lots more calories).
And as slopes get steeper, the oxygen demands and overall energy demands increase rapidly: from 0% to 10% grade it’s around 20% oxygen-use increase; from 0% to 20% grade it’s a 200% oxygen-use increase.
All very interesting. So when you are on the treadmill next time, each % that you increase the grade actually has a compounding effect on your overall energy required. This is reflected in a compounding oxygen demand and – the good news – a compounding increase in calories burned. Plus you’ll be recruiting more and more muscles as the grade increases, which can only be a good thing.
This compounding effect would seem to kick in whenever the grade goes beyond a few % (for 1 -3% grades the additional effort is likely to be only 1 – 5% more)
And so what about my slowness on my Melbourne 1km sprints? Certainly the uphill slope had an influence. My best time in Melbourne was 3% slower than my all-time (3.21 compared to 3.15). We could consider this to mean that the Melbourne run required 3% increase in effort to finish it in the same time as a flat run.
Taking into account the results of the above studies, we can estimate the slope I was running on to be about 2 %. I may never know for sure, but I sure hope it was at least that. If not, and the gradient was below 2% and I was 3% slower, my performance in Melbourne must indeed have been less that what it has been on the flat.
So maybe I was actually just running a little slower – even though I was certainly giving it everything. Does that matter to me?
Not at all. I was away from home, away from routine, and still I was lucky enough to be up early every morning for a short, sharp run. A great way to check out a new city, and always a great start to the day. Plus a cool view of the Melbourne skyline.
That was my view 500m from the finish
I will continue my pursuit of the 3 minute mark for 1km on a flat surface, just so I know exactly how I’m progressing. I’ll save running uphill for when I want to engage a few more muscles and burn a few more calories.