How does the foot leave the ground during running ?

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It is generally accepted that the plantar fascia of the foot fulfills a number of roles during gait and that one of these is the storage and release of energy at different parts of the gait cycle via the windlass mechanism . My question is this .During running when the stored energy is release , what does this energy help to move and in what direction does it move it .

Some time ago I placed a few posts on a site run by Professor Jason Cholewa which touch on this subject .----------

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Hi Jason
A super slow motion version of a professional tennis match shows a large variety of foot contacts and patterns of movement and I should imagine that the mechanics of changing directions and stopping/decelerating varies .
Going back to the subject of concentric contraction of the toe flexors I wonder if you are familiar with a paper entitled ?The architecture and contaction time of the intrinsic foot muscles ? Tosovic et al ,University of Queensland ,2012 .
Based on the contraction time of the muscle the paper suggests a role for flexor digitorum brevis (FDB)which involves the muscle acting to develop rapid ground reaction forces .
It made me think .Might it be that one role of the FDB is to assist in the rapid movement of the foot and leg /lower leg relative to the centre of mass (COM) rather than move the COM itself ?. Think fast feet !
Regards
Blue
Re

Referring to the above might it be that during running and in particular sprinting both the flexor digitorum brevis and the wound plantar fascia act to propel the foot in an initial almost vertically upwards direction causing the lower leg and foot to accelerate relative to the rest of the leg with a subsequent flexing of the knee joint . I am not suggesting that this flexing action is in anyway sufficient to push the foot all the way up to the proximity of the glutes but only that it might assist in the initial flexing of the knee so that the range of motion at which the major knee flexors (semimembranosus ,semitendinosus and biceps femoris ) work most efficiently can be quickly achieved allowing faster recovery and preparation of the reference leg for subsequent strides . My understanding is that the knee flexors work most efficiently at between 20-30 degrees of knee flexion


A second post on Jasons site by me refers to a study which showed that strengthening the intrinsic toe flexors can improve sprint times and perhaps the mechanism described above might be one of the reasons for this . ----

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Hi Jason
On the subject of strengthening the toe flexor muscles of the foot and improved sprint performance I wonder if you have yet had time to read a very recently published paper which showed that strengthening the intrinsic toe flexors led,on average , to an improvement of 0.29 secs over a 50m sprint distance amonst a group of healthy male subjects .
The paper is ? Takayuki Hashimoto ;Keishoku Sakuraba -Strength Training for the Intrinsic Muscles of the Foot ;Effects on Muscle Strength ,the Foot Arch and Dynamic Parameters Before and After Training ; J.Phys.Ther.Sci.26 373-376,2014
The online version of the paper does not contain a photograph of the equipment used to strengthen the toes but the method seems to have involved flexing the toes against a load provided by scales whilst the ankle was kept in a plantarflexed position to reduce the input of the extrinsic toe flexors .
I would be interested in your thoughts
Regards

Finally it may be useful to look at a sprinter moving in slow motion . The video I have in mind can be found here and features Asafa Powell .
The video focuses in on his feet at about 3mins 20 secs into the clip just as he passes the 70 m mark . Just after the feet leave the ground there appears to be a judder at the ankle joint . I am not sure of the significance of this but could it be indicative of the forceful upward propulsion of the foot by the Intrinsic toe flexors and the unwinding plantar fascia timed to co-inside with the unweighting of the foot as the rest of the body moves forwards and upwards .


Asafa Powell Slow Motion Sprint / 100 m?tres ralenti ...
Video for SLOW MOTION SPRINTINGRight-pointing black triangle 4:00
https://www.youtube.com/watch?v=KRZvlQTTCMg
3 Sep 2009 - Uploaded by Richard
Un 100 m?tres de Asafa Powell dans un tr?s gros ralenti r?alis? avec des Cam?ra grande vitesse. Tir? du ...



Any thoughts on the above ?
Gerry
Gerrard Farrell
Glasgow

 

Just because you store energy in elastic tissue, does not mean that energy will later be used for the ideal purpose. Springs when compressed, and released, will release their energy at certain time and velocity. If the released energy doesn't fit your needs it won't aid the motion that you want to create. In tennis, the motions you want to create are quite variable. So, the stored energy might not help you do what you want to do.


The muscle strengthening makes some sense. Ankle plantar flexion energy could be made more efficient by making the foot more rigid so that energy input would go toward motion more than to stored elastic energy that may or may not be used.

Eric

 

How does the foot leave the ground? - Just Like That

https://www.youtube.com/watch?v=W2-U8kV2oA0

 

Scotfoot

You might find this paper informative and of particular interest to your question would be the consideration of the Pedotti butterfly diagram, which is similar for the human foot and you can Google those diagrams for human gait.

 

Hi Eric
I think you are correct that elastic energy generated during movement is not always usefully returned . In the context of tennis this might be especially true since it involves many patterns of movement and changes of direction . I also think it probable that some athletes are better than others at storing and using elastic energy through better timing which may have learned and innate components .
With regard to tennis Roger Federer at his peak made court coverage look effortless .

Going back to the video of Asafa Powell I noticed that at toe off his left heal makes a definite outward movement away from the midline . This is very noticeable in seconds 10-15 during a short slow motion video section . For me the question is what causes this and what is its significance ?

Gerry

Ps A pop up blocks the view of the left foot in the video so you need to cancel this as soon as it appears .