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Your middle-school gym teacher was probably wrong. No, I’m not talking about his or her advocacy on behalf of really short shorts (as we runners all know, short shorts are the coolest.) but what was probably said to you about swinging your arms when you run.

I’ve heard it countless times from athletes I coach—they were told by a gym teacher (or a coach) to pump their arms vigorously. One woman even told me that in sixth-grade PE, the class was told that their hands should hit their pockets with each swing. That form may work for short sprints, but it is completely wrong for longer-distance trail running.

If you learned athletic habits as a kid like I did, you may be misusing your arm swing, and in the process, making running way harder than it needs to be. Three simple fixes can help you overcome bad habits and make your running more efficient than ever.

1. Shorten the levers

A good runner is like a T. rex—ferocious from the waist down and neck up, but unimposing in between. As demonstrated by a 2014 study in the Journal of Experimental Biology, your arm swing is meant to counter motion in your hips to preserve balance, not to propel you forward. The most efficient way to do that is to make like a T. rex and keep your arms close to your body.

Sub-four-minute miler and 2011 U.S. Trail 10K Champion Bobby Mack uses short levers while I use less efficient, longer levers in the background. Photo by Mary Shannon Johnstone

While studies have not found an optimal arm angle, start at 90 degrees. The key is what comes next. Focus on keeping your arm angle at 90 degrees or less throughout the arm swing—in other words, if you draw a line from your shoulder to your elbow to your wrist, it should form a right angle. Don’t let your arm angle open up.

If you watch many efficient road and track runners, their arms often form even shorter levers, sometimes around 70 degrees. By keeping the angle at 90 degrees or less, the arm swing uses less energy, which can then be used where it’s really needed—in the legs.

To put it another way, T. rex arms are essential for Velociraptor speeds.

2. Small swings from the shoulders, not large swings from the elbows

Don’t do as I did in 2012 (left) before I learned the magic of the arm swing. Instead, do as I say—or better yet, copy Andy Wacker (right), pictured here winning the 2015 U.S. 50K Trail Championships. Photos by Mary Shannon Johnstone (left); Richard Bolt (right).

Running efficiently is all about having no excess motion. Simply put, any excess motion in the elbows, wrists or hands is wasted (beyond minor movements caused by being relaxed while moving quickly). Instead, think of your arm swing as confined to your shoulders, where the energy best counteracts your hip rotation and keeps you balanced.

In addition, keep those shoulder-oriented swings relatively small. Throwing your arms about like an inflatable man at a car dealership doesn’t help you run any faster.

3. Focus on a relaxed, passive arm swing

The most important tip of all is the last one—relax. As discussed in the 2014 study, any excess tension in your upper body is wasting lots of energy.

Start with your hands, which should be turned in naturally so that the palms are facing one another. Your fingers should be slightly closed in a delicate fist, as if you are cradling a robin’s egg. Your forearms, elbows and biceps should be completely unflexed. And your shoulders should be the loosiest goose of them all, simply moving the minimum amount that is natural to counteract your hip rotation.

Now that you know the basic principles, I recommend watching a few videos of fast road and track runners during races. Since they cannot afford to waste an ounce of energy in competitions that may be decided by a 10th of a second, their arm swing is usually optimal for their physiology.

Then try to put these tips into practice on your next run. If you are anything like me, T. rex-ing with your arms could lead to Brontosaurus-sized breakthroughs on the trails.

David Roche is a two-time USATF trail national champion, the 2014 U.S. Sub-Ultra Trail Runner of the Year and a member of Nike Trail Elite and Team Clif Bar. He works with runners of all abilities through his coaching service, Some Work, All Play. Follow David’s daily training on Strava here, and follow him on Twitter here.

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