The Science of Hill Running and How It Impacts Your Race Times
Unless you confine your competitions to the track, hills are a fact of life for every runner. Obviously, running up a hill takes more energy than running over flat ground, and running down a hill saves energy, but today we’re going to look at the specifics of hill running: the demands it places on your body, how to get better at it, and exactly how much a hill will slow you down or speed you up.
Hopefully we’ll come up with a better understanding of what’s needed to successfully race on a hilly course and what to expect when encountering hills.
Where does the extra energy to run up a hill come from
On the way up a hill, you’re clearly going to get tired if you maintain the same pace. That’s because you not only have to propel your body forward, but upward, doing work against the force of gravity.
But where does the extra energy to propel yourself up a hill come from? Does it rely primarily on muscular strength or aerobic conditioning?
A recent study by Paavolainen et al. in 2000 set out to answer these questions.1 The subjects in the study were recruited from three groups: triathletes, cross country skiers, and middle distance runners. There was no difference between the three groups in their maximum oxygen intake (VO2 max) during treadmill running, meaning they were all in roughly the same aerobic shape. However, since the middle distance runners focused on running (and moreover, focused on fast running) in their training, they had what the researchers called better “muscle power factors” than the triathletes and cross country skiers.
So on the preliminary treadmill tests, the middle distance runners had better anaerobic endurance, better top-speed as measured during a 30m sprint, and achieved higher concentrations of lactate in their blood during fast running. Each of these three groups was subjected to a treadmill test measuring their efficiency and performance on two progressively faster treadmill tests—one flat and one with the treadmill set at a 7° incline (a 12% grade, a fairly substantial hill).
Surprisingly, the researchers found that aerobic fitness (as measured by VO2 max) was a better predictor of uphill running than the “muscle power factors” for all groups. (Click to Tweet)
So, while the middle distance runners tended to outclass the skiers and triathletes on the flat treadmill test, the groups were more or less equal on the uphill running test.
The upside of this is that, when training for a hilly race, whether it’s a 5k cross country race or the Boston Marathon, you should not lose focus on doing some faster running at close to VO2 max pace (between two-mile and 5k race pace), lest you hurt your uphill running performance. Fortunately, doing uphill repeats is itself a great way to train your VO2 max. But Boston is infamous not so much for its uphills, but for its pounding downhills.
Difference in impact during uphill and downhill running
When going down a hill, running is (at least initially) easier, since gravity is doing some of the work to move you forward. The downside is that you have to absorb significantly more shock on impact.
A 2005 study by Jinger Gottschall and Rodger Kram quantified the difference in impact during uphill and downhill running.2 Using a force plate and an adjustable-incline treadmill, Gottschall and Kram calculated both the impact force and braking/propulsive force. The braking and propulsive forces are the resistances the foot encounters in the forward and backward direction (parallel to the ground), respectively, vs. the downward resistance encountered in the impact force For running at an even pace on flat ground, the propulsive force and braking force are about equal. Ten subjects ran at inclines ranging between +9° and -9°.
Impact forces were 54% greater and braking forces 75% greater while running downhill.(Click to Tweet)
In contrast, the impact force virtually disappeared during uphill running, while the propulsive force increased 74%. This should not be too much of a surprise, since gravity is doing most of the propulsion on the way down, but you have to do it on the way up.
Keep in mind that Gottschall and Kram’s study used a treadmill at a constant pace when taking these measurements—in the real world, when running at an even effort, you will slow down on an uphill and speed up on a downhill. So the effects (particularly the increased impact forces) will be magnified.
What significance does this extra pounding have?
Well, all of that extra impact and braking force has to be absorbed somewhere. The quads probably take the brunt of the increased braking force, while impact is probably dealt with in the same way normal impacts are dealt with, by distributing it through the muscles, tendons, joints, and bones of the legs.
The upside of all of this is that downhill running will be much more strenuous on your body than flat running. Uphill running is a tougher call, since the reduced/eliminated impact force is balanced out by the increase in the amount of power your muscles have to produce.
How to handle downhills in training
Of course, it would be very foolish to avoid all downhill running, especially when training for a race with downhills! So instead, it would make sense to take steps to mitigate the negatives of downhill running while still allowing you to practice it.
- We know that impact forces can be reduced by running on a softer surface or in a more cushioned shoe, so try to avoid long downhills on pavement in thin racing shoes. Instead, do what many high school and college cross country teams do and practice your downhills on grass.
- Additionally, avoid doing too many downhills when you’re already fatigued, like near the end of your long run or the day after a hard workout.
- Finally, balance out the need to practice running downhills by treating it like any other workout: gradually increase your volume and intensity over time. Early on in training, you might do some running on gradual downhills on grass, while later in the year you’d do longer and steeper downhills on pavement, if that’s what your upcoming race calls for.
How to handle hills during a race
There’s one last topic to address when it comes to hills, and that is realism. A hilly course is going to be slower than a flat course, all else being equal.
But how much does a hill slow you down?
Work by Jack Daniels, of Daniels Running Formula fame, produced a “rule of thumb” described by Daniels several years ago online.3 His rule states that every percent gradient of incline (going uphill) will slow you by 12-15 seconds per mile, and every percent gradient of decline (going downhill) will aid you by 8 seconds per mile.
It’s surprisingly easy to figure out the incline of a particular hill, either by using a GPS device or an online tool like gmaps pedometer. So, for instance, the famous “Heartbreak Hill” at the Boston Marathon is about 0.4mi (600m) long and rises 27m. That’s a gradient of 4.5%, and over 0.4mi, we’d expect that segment to be 21-27 seconds slower.
Daniels’ rule is a bit complicated, though, so I like a simpler rule of thumb described by John Kellogg, of LetsRun fame. His rule states that every 10 feet of elevation change alters your time by 1.74 seconds, regardless of the horizontal distance covered. So, six-minute mile effort over a mile which gains 70 feet should be about 12 seconds slow; likewise, a 10k which drops 300 feet should be about 52 seconds fast.
As you can see, Kellogg’s rule doesn’t differentiate between up and down, and it’s fairly obvious to anybody who’s ran a hilly course that you don’t get “back” as much as you put “in” to a hill! Depending on how nitpicky you are with details, pick whichever rule you prefer.
Putting it all together
So, to sum things up, you’ve got to be realistic when it comes to a hilly course. Uphills will slow you down significantly and will tax your maximum aerobic power. Downhills will increase the shock that your legs have to absorb with each step, possibly increasing your risk of injury. And a hilly course is not going to be as fast as a flat one.
- On the upside, preparing for hills in training will give you an advantage when it comes time to race. In addition to practicing running up hills, don’t neglect faster high-end aerobic workouts that train your VO2 max, even if you’re preparing for a longer and slower race like a marathon.
- Practice downhill running judiciously: you want to be prepared when it comes time to race, but not overdo things in training and wind up getting hurt because you ran too many downhills. If you can, practice downhill running in more cushioned shoes or on a softer surface.
- If you want a more concrete idea of how much a hill is going to slow you down, you can use one of the “rules” above to get a rough idea of what to expect. Finally, for more information about the proper form when running up and down a hill, you can read this article on how to run hills.
1. Paavolainen, L.; Nummela, A.; Rusko, H., Muscle power factors and VO2 max as determinants of horizontal and uphill running performance. Scandanavian Journal of Medicine & Science in Sports 2000, 10 (5), 286-291.
2. Gottschall, J. S.; Kram, R., Ground reaction forces during downhill and uphill running. Journal of Biomechanics 2005, 38 (3), 445-452.