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Self-diagnose Your Running Knee Injuries

Last week, we talked about how towatch for hip drop, a common problem withrunning form. Its primary cause is usually weak hip abductor muscles, but even with strong hip abductors, you can sometimes suffer from faulty biomechanics. In other words, even if you are strong enough, your stride may still be “broken.”

As we’ve seen before,one of the most well-identified problems with many runners’ form is excessivehip adduction—when the upper leg slants inwards towards the center of the body during the stance phase. A good bit of research has showed that excessive hip adduction is linked to injuries in the knee,1IT band,2and more. What’s worse, women seem to have a much higher incidence of excessive hip adduction than men do,3possibly accounting for some of the “gender gap” in injuries (while the rate of participation in running between genders is fairly even, women make up 54% of injured runners and 60% of runners with knee injuries).4

While checking for hip drop due to weak hipabductormuscles or poor muscle firing patterns can help, it’s entirely possible to have poor hip mechanics without a perceptible hipdropat the waist.

Evaluating hip mechanics

While researchers use high-tech 3D cameras in gait laboratories to measure hip adduction, those tools aren’t available to the average runner. Another “field test” I particularly like for evaluating hip mechanics is checkingleg crossover.

When running with “good” form and mechanics, your footstrikes should land right on a straight line. If your hip adducts excessively, one leg will “cross over” the other, and your foot will strike across the centerline of your body. For example, if your right hip’s mechanics are faulty, your right leg may cross over to the left side of your body as your foot hits the ground. Because you are effectively putting your weight further towards the left side of your body, this can counteract the hip drop you might otherwise see, thus obscuring your problem.

Now, leg crossover is far from a perfect measure of hip mechanics: sometimes, even though your foot lands in the right place, your knee will buckle inwards, creating excessive hip adduction and knee internal rotation. Checking your footstrikewon’thelp in this case. However, since you won’t be supporting the opposite side of your body as strongly, you may be able to observehip dropin this case.

How to check for leg crossover

Anyways, moving on to how to check for leg crossover. If you have access to a video camera or a treadmill with a mirror in front of it, you might be able to observe it directly. But since catching exactly where the foot falls in a third of a second or less can be tricky, I prefer to measure it indirectly by observing footprints.

The sight of a runner’s footprints on wet sand or freshly fallen snow can give you some clues about his or her hip mechanics by observing how much the left and right foot overlap. Snow and wet sand aren’t easy to come by, but you can make a small puddle of water with a garden hose on a stretch of dry pavement or asphalt, then run through it and continue running in a straight line. Then, looking back at your footprints, you can determine whether your legs are crossing over the centerline of your body.

What leg crossover looks like

The image above illustrates the different scenarios you might see in your shoeprints. On the left is what you’d like to see: a balanced stride where the left and right footfalls overlap by about a third of a shoe’s width. In the middle is a mild crossover pattern; in this case, the left leg is crossing over the centerline of the body and landing on the right side of the body.

Now, you are unlikely to have a thin line on which to run, so in real life, you might need to do some detective work to figure outwhichleg is crossing over if you see that your footfalls are overlapping too much. Usually you can tell by running along a line (either painted on the road, on the track, or on an athletic field) and glancing down to see which is the offending leg.

Finally, on the right is a “wide stance” which is uncommon but does occur. There’s no evidence to indicate that this is injurious or undesirable, but it’s something to take note of nonetheless.

What to do if you do suffer from leg crossover

If youdohave leg crossover, what’s to be done? Whilehip strengthis never a bad idea, in my experience, leg crossover is more likely to be caused by muscle firing patterns than weak glutes (unlikehip drop).

The easiest way to correct crossover is to practice running with good form—i.e.nocrossover—for short stretches of time by running on a track, football field, or soccer field and trying to keep your footfalls even and on one of the painted lines. Avoid doing this on the roads if you can, since you ought to be looking out for cars instead! Continue to work on your form in small doses and develop strong mental cues that remind you of how to run with good form. You can then transfer these mental cues to your normal run for longer and longer stretches. Eventually, you’ll be able to run an entire run without reverting to excessive leg crossover and stave off knee injuries.

In sum, while leg crossover is not a perfect metric for excessive hip adduction, it’s another good “field test” you can do without any expensive equipment or specialized facilities. And it’s a pretty common problem too. Fortunately, with a little practice and a few attentive miles on the track or soccer field, you can keep it under control and hopefully reduce your risk of injury. Retraining your running form is a slow process, of course, so don’t be discouraged if it takes a while to straighten out your legs.

References

1. Ferber, R.; Kendall, K. D.; Farr, L., Changes in Knee Biomechanics After a Hip-Abductor Strengthening Protocol for Runners With Patellofemoral Pain Syndrome.Journal of Athletic Training2011,46(2), 142-149.
2. Ferber, R.; Hamill, J.; Davis, I.; Noehren, B., Competitive Female Runners With a History of Iliotibial Band Syndrome Demonstrate Atypical Hip and Knee Kinematics.Journal of Orthopaedic & Sports Physical Therapy2010,40(2), 52-58.
3. Ferber, R.; McClay Davis, I.; Williams Iii, D. S., Gender differences in lower extremity mechanics during running.Clinical Biomechanics2003,18(4), 350-357.
4. Taunton, J.; Ryan, M.; Clement, D.; McKenzie, D.; Lloyd-Smith, D.; Zumbo, B., A retrospective case-control analysis of 2002 running injuries.British Journal of Sports Medicine2002,36, 95-101.

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 theBoston 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 thatevery 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 thatevery 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 thattrain 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 onhow to run hills.

References

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.
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