The human body is pretty miraculous. It evolved to allow a nearly infinite number of movements: running, climbing, jumping, swinging, and more.

But you mostly use it for one thing: sitting down. You sit in your car or on the subway, you sit all day at your desk, you sit to eat lunch and dinner, and you sit on your couch to binge-watch Netflix at night.

That disjoint – between how your body was evolved to be used, and how you’re actually using it – causes all kinds of problems.

Here’s just one: when you sit, your hip flexors are in a shortened position. And after enough sitting, your body starts to treat that shortened position as the new normal. So when you stand back up, there’s not enough slack in the system. Your hip flexors are permanently tight.

That’s a problem by itself, since so many athletic movements – from running and jumping, to throwing a ball or throwing a punch – depend on generating powerful hip extension. Tight hip flexors oppose that extension, reducing the power you can create. It’s like driving with the parking brake on.

But the secondary effects are even worse. Let me explain:

Perhaps, in the past, you’ve bought beef to cook for dinner, and had to cut off the silver-skin.

Your muscles have silver-skin, too. It’s called fascia. In your body, your muscles cells are held together in bundles, and the fascia is what does the holding together.

In recent years, however, we’ve begun to realize that fascia also connects one bundle to the next, in running lines of tension. As the song says, your hip bone’s connected to your thigh bone. And, similarly, your hip muscle’s connected to your thigh muscle. Which, in turn, is connected to your calves, ankles and feet in one direction, and to your lower back, thoracic spine, shoulders and arms in the other.

In fact, there’s a single run of fascia that extends from your toes, up through your entire body, to your elbows. And your tight hip flexors are right in the middle of that fascia run.

When hip flexors get tight, they take slack out of the middle of the system, creating a game of ‘crack the whip’ that causes problems all the way up and down that chain. Now, your tight hip flexors start causing foot pain, or knee pain, or a bad back, or a tweaky shoulder.

Normalizing the length of your hip flexors, getting slack back in the system, has huge and far-reaching impacts.  It will make you a better athlete, prevent future injuries, and knock out a slew of nagging pains you’ve been living with too long.

Fortunately, you can make big inroads on fixing your hip flexors with just one simple stretch, popularized by Dr. Kelly Starrett. He calls it the ‘couch stretch’, because he and his family do it at night, on the front of their couch while they watch TV.

Here’s a demo, pulled from Composite’s 14-day Jump Start for new clients. (I cover similar topics as in this post for the first half of the video; if you just want to see the stretch, hop to about the six-minute mark.)

To recap:

1. Get on your hands and knees in front of a wall (or, if you can’t peel yourself away from the tube, the arm of a couch).
2. Put your right shin flat vertically against the wall; your knee should be wedged into the corner where the wall and floor meet, and your foot should be pointed so that your instep is against the wall.
3. If you’re not bendy, this may be a stretch already. If you’re more flexible, you can put your left foot flat on the ground.
4. Squeeze your butt. In particular, squeeze your right glute, the side with the foot that’s against the wall. This will help stabilize your low back, and correctly position your hips.
5. While still squeezing your butt, try to lift your upper body upright. Think about making your spine long, extending the straight line between the top of your head and your tailbone. You want to get upright by opening at the hip, and not just by arching your low back.
6. For bonus points, you can eventually work towards reaching both hands overhead, so long as you can do so with tight abs and glutes and with your back long and straight. In the beginning, however, you’ll probably want to use your hands on the floor or on your forward knee, to help push yourself upright. You can also put a box in front of your body, and push up on that.

Now hold that stretch for two minutes. (That’s how long it takes for the Golgi tendon organ receptors to give up, allowing you to reach your full stretch and make lasting change.) Then switch to the other side, and do two minutes on the other leg.

I strongly, strongly suggest timing yourself, as two minutes is waaaaaay longer than most people tend to hold a stretch by default otherwise. (Side note: interestingly, dentists similarly recommend toothbrushing for two minutes. There, too, without using a timer, most people average brushing for only a third of the recommended time. If you like having teeth, consider deploying your two-minute timer next to the sink while brushing, much as you do while Couch Stretching.)

The most common problems to guard against while doing the Couch Stretch:

1. Your rear knee isn’t against the wall. Even if it means you can’t get your opposite foot up on the ground, keep your rear knee / shin / foot all the way up against the wall. That takes all the slack out of the system, making the stretch much more effective.
2. Your forward foot is too close in. Take a big step forward with that foot, so that your forward shin is vertical, too.
3. You’re over-arching your lower back. Hyper-extending your lumbar spine is a very common (and not very good for you) habit in general; it’s even more common in something like the couch stretch, where it’s easier to bend at your low back than to actually stretch the hip flexors you’re gunning for. Think about making your spine tall, and about keeping your low back flat, even if that means you can’t get as far towards upright.
4. You’re making a ‘pain face’. Effective stretching isn’t a relaxing experience. Done right, the couch stretch is hard work! At the same time, it’s important not to grimace while doing it (more technically called ‘facial fixing’), which actually undercuts the neurological effectiveness of the stretch. Breathe, go to your happy place, and try to keep your face serene. It’s zen and the art of stretching!

That’s it.

Try it daily for the next two weeks; I suspect you’ll be pleasantly surprised by the huge positive impact.

If you’re an average, 180-pound person, all the capillaries in your body – the smallest blood vessels, where oxygen and other nutrients are exchanged with cells – can together hold about 3 gallons of blood.

But blood, like water, is heavy. So you evolved into a evolutionary compromise. Your body only contains about 1.5 gallons of blood at a time; much lighter to carry, but only half of what you need to provide for your whole body at once. Fortunately, your body also evolved a smart system of hemodynamics, a combination of forces that sends that blood to capillaries as it’s needed.

At the front end, your heart pushes oxygen- and nutrient-rich blood through your arteries.

Then the movement of your muscles pulls that blood from your arteries into your capillaries, to feed individual cells.

In other words, while your heart is circulating blood all the time, the oxygen and nutrients only make it to cells when the muscles around them are moving.

That’s one of the major problems with excessive sitting: without movement, your cells are starving.

But that’s just one problem. After 30 minutes of sitting, your metabolism slows down by 90%. A few hours in, you’ve got increased blood triglyceride and insulin levels, and reduced (good) HDL cholesterol and lipoprotein lipase (an enzyme that breaks down fat in your body).

So perhaps it shouldn’t be surprising that people who sit more are sicker and fatter than people who don’t.

What’s more, that’s independent of exercise. Even between people who work out for the same number of hours weekly, a greater number of hours spent sitting each day correlates with an increase in both body mass and all-causes mortality. Studies have tied sitting to huge increases in everything from type 2 diabetes to cardiovascular disease and cancer.

For example, excess daily sitting increases your risk of lung cancer even more than the second-hand-smoke effects of living with a smoker.

All of which is bad news, because we apparently really love to sit. The average desk worker spends 7-8 hours a day sitting at the office, then comes home to sit down for another 5 hours of daily TV.

Fortunately, the solution is simple: get up frequently and move around.

Research has shown that even short breaks (a couple of minutes) at low intensity (walking to the bathroom, or simply standing up) make a huge difference. One study showed that, the greater the number of breaks taken, the lower the waist circumference and BMI, and the better the blood lipids and glucose tolerance.

Of course, once you get into the flow of work, it’s easy to forget just how much you’re sitting. That’s why you need some gentle nudges:

First, several fitness trackers can provide regular reminders to move. You can make sure those alerts are set up on your Apple Watch (more info here), Jawbone (see “Idle Alerts” here) or Garmin Vivosmart (info on the “Move Alert” here).

Second, as most people carry a smart-phone at all times, a simple hourly chime app (like Chime for iPhone and Hourly Chime for Android) can be a suitable reminder. When you hear a ‘ding’, stand up for a minute or so. If you’re feeling saucy, you can set those apps for more frequent reminders – say, every 30 minutes. (These are particularly handy in the evening. If you’re watching TV, for example, you can keep watching, just stand up and move a bit for a minute or two while you do.)

Third, since people are most likely to sit for extended periods of time while working on their computers, it’s also worth adding in an even more insistent reminder on-screen. Breaktime for Mac or Rest for Windows will take over your screen at whatever interval your select, reminding you to stand up, shake it out, go the bathroom, grab a water or coffee, or similarly get that mini-dose of movement it takes to get your body back on track.

This one’s an even smaller habit than most – again, it just requires getting up and moving briefly throughout the day. But it’s also one of the most effective you can implement in your life.