In todays post, Join Dr Ivo as he talks about common “Power Leaks” that occur in runners. It really is as simple as P = W/t !
The Gait Guys. Breaking it down to understandable terms with each and every post.
What were they thinking?
You have heard us talk about the normal lines of force as they travel through the foot. In the drawing above you will see several options of force travel through the foot, the one that makes it through the big toe is typically the most normal and advantageous. They begin at the lateral heel, travel up the lateral column of the foot to the head of the 5th metatarsal, go across the transverse metatarsal arch (or more appropriately, transverse metatarsal area) to the head of the 1st metatarsal, and out through the center of the hallux (or big toe). Again, look at the left portion of the diagram on the top.
You have also heard us talk about tread patterns on the bottom of the shoe or outsole. The “lines” or siping should work in concert with the forces as they travel through the foot.
Now look at the diagram on the right. Something is awry here. Do you see it? Why do the treads stop at the tail of the 5th metatarsal (base of the little toe’s metatarsal)? Why does the siping that travels the length of the foot go from the medial (inside) of the heel to the lateral (outside) part of the foot? Depending on where on your foot you strike the ground, this could seriously change the direction of force though the foot.
Look at the bottom of footwear. Look at the lines that the forces will follow. Something that “looks cool” may not actually be so cool for our biomechanics!
The Gait Guys. Stretching your brain each day : )
Drawing courtesy of Tom Michaud.
All material copyright 2012 The Homunculus Group/The Gait Guys. If you want to use our stuff, PLEASE ASK 1ST!
You evidently can’t have your cake and eat it too…
Here is more research to show that running in shoes give you a mechanical advantage in force generation, but at the cost of increased stress on the knees.
“The results imply higher mechanical stress in shod running for the knee joint structures during midstance but also indicate an improved mechanical advantage in force generation for the ankle extensors during the push-off phase.”
No surprise really. You could swing a broomstick with little effort and a baseball bat with more effort, but which will hit the ball farther? Which may tax your shoulder more?
Whenever we take a foot, that SHOULD supinate, effectively decrease its mobility (making it stiffer) and MAKE IT supinate, we will have more power. Remember P = W/t? P is power, W is work and t is time. W is also F X s, where F is force and s is displacement; so we have P= Force X displacement/time. We are increasing displacement here: with force and time remaining unchanged, we have more power.
But…all things wear out in time with use; including your joint cartilage. Hmmm, maybe we reduce the force and allow the joints (like the ankle) to displace (we see increased displacement in unshod running) and we run into our 100’s.
The choice is yours.
The Gait Guys: 2 docs, making a difference, one step at a time.
J Biomech. 2010 Aug 10;43(11):2120-5. Epub 2010 May 11. Footwear affects the gearing at the ankle and knee joints during running. Braunstein B, Arampatzis A, Eysel P, Brüggemann GP. Source
Institute of Biomechanics and Orthopaedics, German Sport University Cologne, Germany. braunstein@dshs-koeln.de
Abstract
The objective of the study was to investigate the adjustment of running mechanics by wearing five different types of running shoes on tartan compared to barefoot running on grass focusing on the gearing at the ankle and knee joints. The gear ratio, defined as the ratio of the moment arm of the ground reaction force (GRF) to the moment arm of the counteracting muscle tendon unit, is considered to be an indicator of joint loading and mechanical efficiency. Lower extremity kinematics and kinetics of 14 healthy volunteers were quantified three dimensionally and compared between running in shoes on tartan and barefoot on grass. Results showed no differences for the gear ratios and resultant joint moments for the ankle and knee joints across the five different shoes, but showed that wearing running shoes affects the gearing at the ankle and knee joints due to changes in the moment arm of the GRF. During barefoot running the ankle joint showed a higher gear ratio in early stance and a lower ratio in the late stance, while the gear ratio at the knee joint was lower during midstance compared to shod running. Because the moment arms of the counteracting muscle tendon units did not change, the determinants of the gear ratios were the moment arms of the GRF’s. The results imply higher mechanical stress in shod running for the knee joint structures during midstance but also indicate an improved mechanical advantage in force generation for the ankle extensors during the push-off phase.
