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Toe flexor strength measurement and falls prevention

Discussion in 'Biomechanics, Sports and Foot orthoses' started by scotfoot, Oct 20, 2016.

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  1. scotfoot

    scotfoot Well-Known Member


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    With regard to measuring toe flexor strength I believe it is important to considered measuring toe strength with the toes in a dorsiflexed ,toe off like position . This is particular true if toe strength is to be looked at in the context of falls prevention .
    The following method ,which would use a pressure mat/force plate combination to measure generated forces ,may allow this type of measurement .
    Use of the system would require the direction of a suitably qualified examiner for accuracy and safety and it would not be attempted by an individual at home or injury may result .

    PRESSURE MAT / FORCE PLATE SYSTEM
    INTRINSIC MEASUREMENT (position 1)
    The method would simply involve the subject standing with one arm out stretched touching a wall and with the reference foot in an late stance position on the pressure mat /force plate so that the ankle is flexed but the toes dorsiflexed .The subject would then be asked to push forwards against the arm/wall by flexing the rear toes . This might give a more accurate idea of the strength of the intrinsics .
    The stance would also involve having the shoulder of the extended arm positioned behind the forward foot placement .
    For clarity , the front foot would be about 2 feet in front of the rear or reference foot .The method might give the most functionally accurate idea of intrinsic toe strength particularly as it relates to the establishment of a stable position after a balance perturbation such as a trip .

    EXTRINSIC MEASUREMENT (position 2)
    The extrinsic toe flexors are thought by some to function isometrically during gait so this is probably the best way to measure there capacity .
    Again all that is required is the mat/plate and a wall . The idea is to measure the force that can be applied THROUGH the toes and not applied BY the toes .

    The test subject stands with the test foot on the pressure mat but now with there back to a wall . The heel of the test foot would be about 6 inches from the base of the wall . The non test foot is moved fowards about a 40 cm and makes light contact with the ground to avoid loss of balance . With their lower back touching the wall the subject now leans forwards at the waist till the COG is just over the MTFI of the test foot (. The forward foot keeps this stable ) . The subject is asked to stay in a forward lean but drive through their test foot toes to push there lower back against the wall as hard as possible .
    The result would give a good Idea of the max force that could be exerted THROUGH the toes to avoid forward progression of the COG over them and hence of the combined intrinsic and extrinsic toe strength .

    RATIONAL BEHIND THE POSITIONS
    The rational of the positions is that in a trip situation position 2 represents the foot acting as a lever arm against which the muscles of the body can act to slow the forward progression of the COM and also allow the contralateral hip to slow in absolute terms but accelerate relative to the contact side allowing any necessary additional strides to be taken in time to avoid a fall .
    Once forward progression of COM has been stopped the COM will be either directly over the blocking or forward foot but will most likely be behind this foot . This means that the COM will begin to move backwards and inwards unless the posterior leg can stop this movement and achieve equilibrium . This is were the 1 position is relevant .

    MEASUREMENT DEVICE
    A pressure mat system would be placed on top of a force plate and secured to it via, for example ,a temporary glue . This would allow both vertical and horizontal force components to be measured and collated .
    With regard to the above it might also be reasonably assumed that if the two named measuring position are valid then these would also be valid isometric strengthening positions .
    Any thoughts ?
    Gerry

    DISCLAIMER -- As far as I am aware the measurement and strengthening positions mentioned in the text above are untested and it is important to note that I am not recommending their use but merely putting them up for discussion .
    The author accepts no liability for any injury resulting from using the positions mentioned in the above text.
    Unsupervised use of the said positions may result in injury .
     
  2. efuller

    efuller MVP

    The purpose of walking is to move the center of mass. Tripping occurs because the swing leg is prevented from getting out in front of the center of mass. The act of walking is vaulting over the stance leg, while putting the swing leg out in front of the center of mass so that the momentum of the body can vault over the swing leg as it becomes the next stance leg. Lack of clearance of the swing leg is the reason for tripping (e.g. weak ankle dorsiflexors) and not weak toe flexors during stance. In walking, the goal of the body is to move the center of mass forward, not prevent the movement of center of mass.
    Eric
     
  3. Craig Payne

    Craig Payne Moderator

    Articles:
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    I don't necessarily disagree and it does make intuitive sense, but it could be highly likely that the values between strength testing when dorsiflexed correlate highly with them when they are fully extended.
     
  4. efuller

    efuller MVP

    I agree that ankle position matters for flexor hallucis longus, but not so much for flexor digitorum longus. FHL goes much further behind the ankle joint axis and has a much larger lever arm, at the ankle joint, than FDL. The muscles have a finite amount of distance that they can shorten. Especially pennate muscles. You can see people that have very strong hallux ipj plantar flexion with the ankle dorsiflexed and can't plantar flex at all with the ankle plantar flexed. Some of the total tendon excrusion is used up by ankle joint motion because the tendon has to move with ankle joint motion.

    On the other hand FDL tendon is much closer to the ankle joint, so ankle joint position matters much less for FDL.

    Eric
     
  5. scotfoot

    scotfoot Well-Known Member

    Eric
    The thread is more about recovery from a trip than how a trip or balance perturbation occurs .
    Craig
    There may well be a close correlation for most but in individuals where this is not the case it may be a sign of reduced ability to regain a balanced position after a perturbation .

    Regards
    Gerry
     
  6. efuller

    efuller MVP

    Gerry, I was disagreeing with the premise in the rationale. When the trip occurs the center of mass has passed the point where using the toe flexors can save you from a trip. I'm talking about the physics of how toe flexors could possibly aid recovery.

    You wrote:

    The rational of the positions is that in a trip situation position 2 represents the foot acting as a lever arm against which the muscles of the body can act to slow the forward progression of the COM and also allow the contralateral hip to slow in absolute terms but accelerate relative to the contact side allowing any necessary additional strides to be taken in time to avoid a fall .
    Once forward progression of COM has been stopped the COM will be either directly over the blocking or forward foot but will most likely be behind this foot . This means that the COM will begin to move backwards and inwards unless the posterior leg can stop this movement and achieve equilibrium . This is were the 1 position is relevant .
    To stop, or slow, forward progression the center of pressure of ground reactive force has to be anterior to the center of mass. The ankle plantar flexors, more than the toe plantar flexors, can shift the center of mass anteiorly, but only by the length of the foot and toes. If the center of mass is already over the foot when the trip occurs, then it is too late for activation of the toe flexors to shift the center of pressure forward. A trip occurs when the swing leg encounters an obstacle that slows the swing leg enough that it can't be placed far enough ahead of the body for the normal forward momentum to allow the usual vaulting of the body over the soon to be stance foot. The trip usually occurs at the lowest point of swing and that is when the swing foot is even with the stance foot. When this happens the center of mass is over the stance foot.

    In fact, one the center of mass is anterior to the center of pressure, contraction of ankle and toe flexors would tend to accelerate the whole body forward rather than pull the body backward over the ankle. At this point the lever of the foot will propel the body forward.

    Eric
     
  7. scotfoot

    scotfoot Well-Known Member

    Hi Eric
    I know exactly what you mean and if the COM is past the standing foot when a trip occurs then it is the foot involved in the initial recovery step that the rational applies to and so on for any subsequent steps .
    The rational would apply to the standing foot if the swing leg is delayed by an obstruction such as a step or roadside kerb (curb) or in older individuals employing a shuffle type walk with very little leg swing where the trip occurs before the COM is past the standing foot .

    Regards
    Gerry
     
  8. NewsBot

    NewsBot The Admin that posts the news.

    Articles:
    1
    Reliability of doming and toe flexion testing to quantify foot muscle strength
    Sarah Trager Ridge et al
    Journal of Foot and Ankle Research201710:55
     
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