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# The Physics of Running

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## lesley roquet

on 12 May 2014

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#### Transcript of The Physics of Running

The Physics of Running
To understand the basic physics of running, you need to think of your arms and legs as pendulums. A pendulum's velocity depends on the length of the pendulum, not the mass at the bottom. If a pendulum is shorter, the speed of the mass at the bottom is faster. Think of your feet as the mass at the end of the pendulum. In order to shorten the pendulum, you bend your knees, which in turn makes you go faster. You also use the same concept with your arms.
The speed of a runner is determined by the distance traveled with each stride (stride length) and the number of strides taken in a given amount of time. Stride length times stride frequency equals speed.
For instance, five ft per stride times three strides per second equals a speed of 15 ft per second.
In order to increase your speed, a runner must simply increase either their stride length or the number of strides in a given amount of time.
For instance, if you increase the stride frequency to four strides per second and reduce the stride length to 4 ft per stride it would result in a speed of 16 ft per second therefore increasing your speed.

Physics state that if your foot lands in front of your body’s center of mass it will act like a brake. An out in front foot strike is causing excessive muscle use and is
more prone to cause injuries. Furthermore, it puts the leg almost in direct line with the body’s motion so it will receive a great amount of impact stress.
Foot Strike
Taking relatively short but frequent strides minimizes braking and bouncing. Leaning forwards slightly creates a natural forward momentum. Leaning forward more will increase propulsion (forward motion energy) and result in faster running speed. By cooperating with the force of gravity it propels you forward without having to use your leg-muscles nearly as much.
Body Lean
*Heel-strike: The most common type of foot strike, but it brakes momentum and is a hard strike that may cause pain and injury.

*Mid-foot strike: The preferred type. A good mid-foot strike is when most of the impact is handled by the ball of your foot, while the heel only slightly touches the ground.
Types of Foot Strikes
*Forefoot/Toe-strike: Is preferred over a heel-strike, but if you over do it by relying on the forefoot for support, you could put too much stress on the calves and cause injury.
The Law: Energy expenditure is directly proportional to how much you go up and down. If you can minimize up and down movement, you can lower your energy expenditure. The more you lean forward when you run, the more it adds a horizontal component to your energy usage.
Basic Physics of running..
How to increase speed of an athlete
Good Foot strike:
Good forward lean:
Work Cited:
Dreyer, Danny. "The Physics of Running." - Chi Running. ChiLiving, Inc, 30 Apr. 2001. Web. 01 May 2014.

"Correct and Proper Running Technique & Foot Strike." Correct and Proper Running Technique Foot Strike. Jollyguru.com, n.d. Web. 01 May 2014.

Mahon, Rollo. "Barefoot Performance Academy." : THE PHYSICS BEHIND RUNNING FORM. Barefoot Performance Academy, 18 Apr. 2013. Web. 01 May 2014.

"Running Physics." Running Physics. Tripod, n.d. Web. 01 May 2014.

"Running Physics." - Training, Exercise, Leg, Strength. Faqs.org, n.d. Web. 01 May 2014.
The key to letting your lean do the work is to have good posture. When you lean, you should lean from your ankles, not from your waist. The more you lean, the faster you go. You cut the workload on your legs in half! Instead of pushing, you are being pulled!
"Your legs will follow your arms, so your arm swing is very important. You need to try to keep your arms relaxed and not let them get too high."
-Betsy Luck
"Even if you have a good lean you need to keep your head and eyes up. Looking down actually shortens your stride length so you want to keep your eyes ahead."
"You want to find a happy medium for your stride length because you don't want to over or under stride."
-Mike Comfort
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