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Strengthening intrinsic and extrinsic foot muscles

Discussion in 'Biomechanics, Sports and Foot orthoses' started by LuckyLisfranc, Nov 10, 2005.

  1. LuckyLisfranc

    LuckyLisfranc Well-Known Member

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    Dear all

    Forgive me if this has been debated before, but I havent found a thread related to it yet.

    I have been in discussion with some students and podiatrists about the relative merits of strengthening intrinsic and extrinsic foot muscles to treat mechanical pathology.

    e.g. strengthening tibialis posterior for hindfoot valgus related pain, or
    stengthening forefoot intrinsics to stabilise hammertoe deformity

    I have always spurned the benefit of doing any strengthening work on these muscles, as anecdotally I have NEVER seen any benefit (either due to poor compliance, or the magnitude of wt bearing forces involved).

    Is there any evidence to prove or disprove the benefit of strengthening work on muscles related to foot function, beyond clinical experience?

  2. Craig Payne

    Craig Payne Moderator

    There is next to no data. Weakness of inversion strength has been shown not to be associated with a pronated foot (Snook, 2001). Basmajian et al (1963) showed that the muscles did not play a role in the support of the medial longitudinal arch. Gray (? year) showed that the leg muscles are more active in those with flat feet. .... so not sure how strengthening muscles would help here as weakness is not apparent and the muscles are working hard anyway.

    Intuiton would suggest that strengthening exercises are good thing to do anyway and exercises would be definitely good if a weakness was the cause of the problem. The problem is, how often is a weakness a cause of the problem?

    Take a pronated foot due to forefoot varus --- does not matter how strong the muscles are, that medial column has to get to the ground. Take someone with tight calf muscles --- the tibia has to move over the leg during gait, if it can't, then the mid foot collapses (pronates) ---- does not matter how strong the muscles are, the tibia still has to move over the foot; etc etc

    As for the intrinsics, we had some discussion here. My argument is basically, that the instrinsics do not fire until weight starts to off load from the heel (ie late midstance), so strengthening is not going to have any influnce on events that occur prior to then.

    To complicate things further, often when a muscle 'weakness' is identified, is it really weak or just has a poor lever arm to the axis of rotation of the joint. How many take into account the STJ/rearfoot axis when doing inversion/eversion strength testing? A 'weaker' muscle may just have a poor lever arm, due to normal individual variations of the joint axis --- the muscle may actually be quite strong, so what use is strengthening?
    Last edited: Nov 10, 2005
  3. efuller

    efuller MVP

    Tissue stress. If the plantar fascia resists arch flattening then any other muscle that reisits arch flattening could take stress off of the fascia. The abductor hallucis has essentially the same origin and insertion as the plantar fascia. When the abductor hallucis contracts there will be a smaller need for tension in the fascia. However, if the pathology is at the 1st MPJ additional compression from muscle contraction may not help the MPJ.

    As I have gotten older, I have noticed loss of strength seems to occur more quickly. I would take my kid for a hike with him in a back pack. My posterior tibial muscle would be sore the next couple of days. Then a hike a few days later would not cause the soreness. The activity caused strengthening of the muscle. This the reason that I tell patients, especially weekend wariors, to start slowly and build into the duration of their activity.

    Craig's point about defining weakness is a good one. A muscle can be strong and have poor leverage and therefore not produce as much moment as another person.

    I have no evidence, but it sure seems like it should help.

  4. I think that the strength and endurance of muscles makes a huge difference toward the overall mechanics of the individual during gait.

    In regards to the absolute strength of muscles, if we take two foot from different individuals with identical abnormal osseous and ligamentous structure, such as a medially deviated STJ axis in stance, and give one individual strong extrinsic and intrinsic muscles and the other individual relatively weak muscles, do you think you would see a difference in function of these two individuals, even though all other "biomechanical measurements" are identical? Of course you would, since the stronger individual has increased capacity to generate the necessary joint moments to allow more normal gait function whereas the weaker individual will have decreased capacity to generate the joint moments necessary, and, as a result, will have a more abnormal gait pattern.

    In regards to endurance of muscular activity, the individual with greater strength will generally be able to generate higher absolute magnitudes of contractile activity in their muscles over a longer period of time for improved endurance when compared to the weaker individual. However, we must also be aware that if two individuals of the same absolute muscle strength are compared and one has low endurance (i.e. higher percentage of fast-twitch muscle fibers) while the other one has high endurance (i.e. higher percentage of slow-twitch muscle fibers), then over time, in performing a repetitive activity using those same muscles, the individual with high endurance will fatigue less rapidly and will likely show lesser degrees of gait changes over time than the strong individual with low endurance.

    The intrinsic muscles of the foot are very important during the midstance and propulsive periods of gait to stiffen the longitudinal arches of the foot and to also help offer another layer of redundancy (thanks Eric) to the arch structure (i.e. to assist the deep plantar ligaments, plantar fascia, PT, FDL, FHL and PL extrinsic muscles in causing a forefoot plantarflexion moment). I would predict that intensive strengthening program devoted to these muscles may not only help alter the kinetics but also the kinematics of gait, and may be able to lessen some of the pain from such pathologies as plantar fasciitis, dorsal midfoot interosseous compression syndrome and plantar ligament stress syndrome. One problem is getting patients to do the exercises regularly enough to cause enough difference in muscle strength. In addition, if these muscles are working in a foot that has a low longitudinal arch height, they would then have insufficient mechanical advantage to generate forefoot plantarflexion moments that would cause gait kinetic and kinematic changes. Therefore, the plantar intrinsics require much more research and work to figure their exact function.

    To generate motion in a foot, a moment must be generated by some source. If the moment is being generated by a tensile force in ligament or muscle or tendon, then the greater the moment arm of that anatomical structure to the joint axis in question, then the greater the magnitude of moment that the muscle, tendon or ligament can generate across that joint axis.

    If an individual is very strong and is able to generate a tensile force in their posterior tibial (PT) muscle of 400 N (90 lbs), but also has a STJ axis that is severely medially deviated so that the supination moment arm length of the PT tendon is only 1 mm, then this individual, with all their PT muscle strength, will only be able to generate 0.40 Nm of supination moment. However, another individual has a relatively weak posterior tibial muscle that can only generate 40 N (9 lbs) of contractile force but has a normal STJ axis location that has supination moment arm of the PT tendon of 20 mm in length, this individual with a relatively weak PT muscle will be able to generate 0.80 Nm of supination moment, or in other words, will be able to resist STJ pronation moments with their PT muscle 100% more than the strong PT muscle individual with the severely medially deviated STJ axis.

    Understanding these basic mechanical concepts is critical to the clinician understanding such pathologies as PT tendon dysfunction, plantar fasciitis and functional hallux limitus since these pathologies can all be easily modelled using the ideas presented above. The clinician that does not understand these concepts will continue to wander aimlessly in a sea of uncertainty regarding the factors that cause painful mechanical pathologies in the feet and lower extremities of their patients and will be unable to offer their patients the best in mechanical foot therapy for their patients.
  5. Cameron

    Cameron Well-Known Member


    Budin (circa 1940) in the US wrote about toe traction (orthodigita) and orthopaedic surgeon, Lambranudo (in TT Stamm's book) about the same time described intrinsic foot muscle exercises. Many of these found their way into foot health forums for children. So picking up pencils by contraction and relaxation of the long and short flexors and extensors came from this source. Circumduction of the hallux was also thought to improve HAV (why is not clear) Maybe because of the war years less emphasis was placed on orthopaedic intervention prevention was thought more appropriate again is not clear but might explain why stretching and exercise became popular. Post war as public school screenings became vogue in the UK then a reinterest in stretching and active exercise was evident within the literature (particularly so in chiropody). Ian Coates kept the thought process current in both US and UK for the next twenty years when he introduced fluid silicones in the late 60s. Toe props for example acted as passive exercisers during stance phase.

    Hey what do I know?
  6. Charlesworth

    Charlesworth Member

    Silicone digital prostheses


    I would just kile to add a rider to what Cameron wrote on silicone digital devices; viz. that Cameron wrote an excellent literature review on the subject during the early 1990s (circa 1993 I think) in the British Journal of Podiatric Medicine. It is well worth a read!!!

    Best wishes,

  7. What a great thread. This is why I joined this forum. I am conducting elementary research on high end winter athletes and feel- at least for pro skiers- the intrinsic muscles are the key to success for support and stability.

    The ability to strengthen these muscules is key.

    / looking forward to reading more in this thread.
  8. scotfoot

    scotfoot Well-Known Member

    Hi Skiing -in -Jackson
    I wondered why the intrinsic muscles are so important to skiers and what steps they take to strengthen them . I have an interest in this area .
    Kind Regards
  9. Do you work in the industry?
  10. scotfoot

    scotfoot Well-Known Member

    Hi Stephen
    I do not work in the skiing industry but am involved in looking at new methods of strengthening the intrinsic and extrinsic muscles of the foot .I was interested to see this particular thread being revisited and wondered what form your research might take . Unlike LuckylisFranc, the originator of this thread, I have seen some anecdotal evidence that benefits can be derived from strengthening the muscles of the foot and in particular the intrinsics . The same anecdotal evidence also suggests that FBOS can be improved both mediolaterally and anteroposteriorly.
    Kind Regards
  11. I'm not super prepared to make the big answer yet as I don't want to look silly in front of all you Dr types.

    Essentially, the ability of a skier to make the subtle movements required for advanced and expert level skiers (and other athletes- mainly non gait sports like cycling) I believe can be enhanced by stronger intrinsic muscles.

    Orthotics and inserts of varying types are very popular with skiers of all ability. As a ski guy, I strongly feel these enhance the user experience in numerous ways.

    But... the ability of the recreational skier to tolerate the orthotic at the beginning of the season when foot and lower limb muscles aren't as strong as they should be may be enchanced by stronger intrinsic muscles.
  12. scotfoot

    scotfoot Well-Known Member

    Hi Stephen
    How would the strengthening of the intrinsics in recreational skiers be acheived .
    Kind regards
  13. I'll get back to yoy whan I get it all figured out.

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