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If you are like most runners, you will have at one time or another had friends tell you they can’t run because of “weak knees.” You may have wondered if this is a fate that might someday befall you.
But the reality is that weak knees are rare. “Knees are inherently very stable joints,” says Laura Matsen Ko, an orthopedic surgeon (and collegiate All-American) in Seattle. When difficulties arise (other than traumatic injuries or arthritis), the knee tends to be the victim of problems occurring elsewhere, she says, often involving weak or imbalanced muscles.
Historically, the go-to line of attack has been to strengthen the quadriceps, on the front of the thigh. But while that is definitely important, kinesiologists and physical therapists are realizing that this is only part of the puzzle. The other, at least as important, lies on the opposite side of the leg: the hamstrings.
Reins for Controlling the Knee
“The hamstrings are like the reins on a horse,” says Matt Walsh, a physical therapist in Portland, Oregon, who specializes in running-related pain and performance.“They keep control of the joint. When they’re doing the job perfectly, it’s like not having to use the reins very much.”
The quads, he says, are the power muscles that do most of the work of propelling you forward. “But to control the forces across the knee you need to have the hamstrings balancing the quads.” When the hamstrings aren’t strong enough, he says, the knee doesn’t really know how to track with each stride and its bones will be “slamming into each other” with each footfall.
Strengthening these muscles can even work for people with chronic knee injuries. A case in point is Jennifer Seibel, a masters runner from West Linn, Oregon. In 2017, an MRI revealed that she had severe chondromalacia — an arthritic condition affecting the cartilage on the back of the kneecap — severe enough that even walking was a painful hobble.
“Before my diagnosis, running was all I was doing,” she says. But a good sports physician convinced her that this wasn’t necessarily the death knell to her running career. “It wasn’t my knees that were weak, but the muscles around them,” she says. Today she runs pain-free, 40–45 miles a week.
Power from the Hip
In addition to sparing your knees, strong hamstrings can also help make you a more powerful runner.
That’s because they affect two joints: the knee, and the hip. At the knee, their primary job is to resist impact and act as shock absorbers. At the hip, they do the reverse and contract to produce power. “They stabilize at one [end] and drive at the other,” Walsh says.
“Everybody gets all excited about the glutes,” he says, “but the hamstrings contribute significantly more extension at the hip than the glutes. If you really want to push at the crest of a hill, it’s the hamstrings, not the glutes, that will do it for you.”
Hamstring Bridge on a Ball Exercise
There are a number of ways to strengthen your hamstrings, but one the best is hamstring bridges on a ball — something you can do on your living room floor a few times a week, while watching TV.
In their simplest form, hamstring/glute bridges start by lying on the floor, then raising your pelvis upward, with your weight split between your feet and shoulders. Imagine that your hips are on a pully, rising straight up. Spread your arms, palm down, to balance side-to-side. Changing the location of your feet closer or farther away from your shoulders will alter the amount of work done by your glutes or your hamstrings.
From the basic bridge, you can graduate to doing bridges with your feet on a surface higher than your shoulders, such as a stack of books or a couch or ottoman. Or do them one-legged — something Seibel credits with helping her return to pain-free running.
But the granddaddy of all hamstring bridges is to do them on an exercise ball, rolling the ball back and forth as you maintain the bridge, building up to maybe 10-15 reps per set. If you are looking for a single exercise most likely to give you happy hamstrings and “strong” knees, this is probably it. (Note: some people call these hamstring curls on a ball, rather than bridges.)
Here’s how to do the exercise:
Beware: this is surprisingly demanding, so don’t plan a race or speed session the next day.
Running-Specific Strength and Control
Part of the magic, Walsh says, is that it mimics the functioning of the hamstring while running. As you roll the ball away, then stop it, it simulates what happens when your foot hits the ground because you wind up stopping it just before your knees are fully straight, at about the same angle as at the time of footstrike. “Roll out, stop on a dime, and bring it back in,” Walsh says, adding that the emphasis should be on controlling the ball on the way out, and then stopping it.
Jay Dicharry, a Bend, Oregon, physical therapist and author of Running Rewired: Reinvent Your Run for Stability, Strength, and Speed, concurs. There is no one best exercise for everyone, but this one, he says, “works the hamstrings in a very similar motion to the running cycle.” For best results, he adds, raise your hips as you draw the ball toward you, so that you keep the thigh and torso in-line at all times, rather than allowing the hip to flex as you draw in the ball. “[That’s] more similar to the timing and movement of the leg in the natural running gait,” he says.
When this too becomes easy, reduce the degree to which you splay your arms to keep yourself from wobbling side to side. This, Walsh says, creates “lovely, small muscle adjustments in the spine and hip” — neuromuscular control that in running translates to better control over foot placement. Without that control, he says, “foot placement becomes sloppy” — something that can not only be tiring and inefficient but be one of those things that, eventually, victimizes the knee.
From that, you can progress to doing the exercise one leg at a time (not easy), or doing it after a run, when your legs are already fatigued. You can even start doing something simultaneously with your arms, such as working with a light dumbbell. “Something complex and challenging,” Walsh says.
Not that you have to progress that far, if your time and balance don’t allow it. Even the most basic bridges on a ball will probably be the most challenging thing you’ve ever done for your knees…and your overall hamstring strength and performance. Something that — unless you already have world-class hammies — is likely to pay prompt dividends that will encourage you to keep it up.