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Post 83: running mechanics

“Footwear such as sandals or moccasins were invented less than 50,000 yr ago, but the modern running shoe with a cushioned elevated heel, arch supports, and a stiffened midsole was created only in the 1970’s”
 
http://news.nationalgeographic.com/news/2010/06/100609-worlds-oldest-leather-shoe-armenia-science/
 
This is an article that I read a while back talking about the oldest shoe was built about 6,000 years ago. It is not too different from what we know to be a shoe. It covers the foot, has an ability to tighten to the foot and protects the foot from elements on the ground.
 
The standard shoes that we know today were created in the 1970’s. Prior to this, most shoes looked like the typical Keds shoes.
 
“More than 75% of today’s shod runners typically rearfoot strike (RFS, in which the heel first contacts the ground, but barefoot or minimally shod runners more often forefoot strike (FFS), with the ball of the foot landing before the heel, or they sometimes midfoot strike (MFS), with the heel and ball of the foot landing simultaneously”
 
When you run, something has to hit the ground first. This could be the heel, the ball of the foot or both could hit at the same time. This seems like a small point, but what if the type of shoe that you are wearing dictates your running pattern. There’s the old saying that form follows function, but what if the shoes form dictates our function?
 
“…FFS landing, unlike RFS landings, generate no impact peak…Elevated heels also encourage a runner to RFS, even when the foot is slightly plantar flexed, facilitating an longer stride and eliminating controlled dorsiflexion by the plantar flexors during landing”
 
A lot is said here. There is more impact to your body when you heel strike. There is less impact to your body when you forefoot strike. The next jump that is made by some is that an increased impact may lead to increased injury rate. We are not there yet.
 
Also, one loses the ability to control ankle motion when wearing heels. For instance, if you strike the ground with your toes first, the large muscles of the calf control your heel down to the ground. If you strike with your heel first, the smaller muscles on the front of the shin control your toes back to the ground. This is one of the hypotheses behind shin splints, in that the repeated lowering the toes to the ground causes the muscle to be overworked.
 
“…runners switched from an RFS gait in shoes to an MFS or FFS gait when barefoot or minimally shod”
This may be the smoking gun. When you wear standard shoes, you are more likely to strike your heel on the ground first and when you run barefoot, you are more likely to strike the ball of your foot. This is the concept behind people wearing the toe shoes for running (see vibram 5 fingers), as there is less impact on the body when wearing a minimalist shoe.
 
“At a given speed, the cost of transport during running increases approximately 1% for every 100g of added shoe mass”
 
This makes sense right? If the shoes are heavier, then it will require more energy in order to move your foot. This is another reason for lighter shoes during distance running. The lighter shoe will have less padding though. This will cause a change in the runner’s stride patterns. So far a lighter/minimalist shoe takes less energy to run and reduces impact on the body. Not seeing the negatives yet…they exist and will be covered at a later post.
 
“Although higher external dorsiflexion moments in FFS gaits cause higher triceps surae contractile costs, more controlled dorsiflexion during an FFS could perfmit more elastic energy storage and return because the heel descends substantially under controlled dorsiflexion, stretching the Achilles tendon while the triceps surae contracts eccentrically or isometrically”
 
First, the authors are from Harvard. This should explain all of the smartsy language used above. What this means is that when a person lands on the ball of the foot, the calf muscle has to take more of the work than the muscles on the front of the shin. When this happens, this could lead to a problem such as Achilles tendonitis. Also, by loading up the Achilles there could be more energy output from the stretching of the Achilles during the running cycle. Think of a spring. When you pull the spring apart, and then let go…what happens? Assuming you didn’t deform the spring, it bounced right back to its shortened position. Well, assuming your don’t tear the Achilles, it will bounce back to its shortened position, which when running will help to propel the runner forward (depending on the amount of forward lean of course, but this is a topic for another post or discussion).
 
“Another biomechanical difference between FFS an RFS running is knee flexion. RFS runners typically land with the foot in front of the knee, which is more extended and less complaint at strike but then flexes more during stance; in contrast, FFS runners land with an initially more flexed knee and have more knee flexion during impact but flex the knee less thereafter”.
 
I recommend watching videos by Brian Mackenzie or google Dr. Nicholas Romanov to learn more about the FFS style of running. In essence, when you land with a straight knee and a heel strike, you are effectively placing a braking force on your running, meaning that it is slowing you down slightly and you have to overcome the breaking force in order to propel yourself forward again. When you land with a flexed knee and the foot underneath you or better yet, slightly behind you, you are allowing for a propelling force instead of a breaking force. Also, landing on a less compliant knee is no good. If you jump and land on a locked out knee compared to landing on a slightly bent knee, which one will feel better? Please…go try it and come back.
 
“…running in minimal shoes is slightly less costly (on average, 2.41%-3.32%) than running in standard shoes after accounting for the effects of shoe mass, strike type, habitual footwear, and stride frequency.”
 
Essentially running in a minimalist shoe, which in this study was the Vibram 5 Fingers, requires less energy to run the same distance compared to wearing a standard shoe. Although this number seems small, over a long duration race or better yet, over the course of a running career, this could have a great impact.
 
This is a smaller study, so the results will need to be replicated in a larger group, but it is one of the first studies to directly assess the difference between running in a minimalist shoe compared to a standard shoe.
 
Excerpts taken from:
 
Perl DP, Daoud AI, Lieberman DE. Effects of Footwear and Strike Type on Running Economy. Med. Sci. Sports Exerc.2012;44(7):1335-1343.
 
 

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Categories: Physical therapy

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