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Vertical ground reaction forces and sprinting

Discussion in 'Biomechanics, Sports and Foot orthoses' started by scotfoot, Aug 31, 2017.

  1. scotfoot

    scotfoot Active Member


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    It has been shown that when swinging a golf club or accelerating a hammer in the hammer throw ,the generation of increased ground reaction forces through the feet can accelerate the arms and held implement if force generation is timed properly .
    My question is ,during sprinting , can the forward and downward swinging comtralateral leg be accelerated along its course by the application of timed ,vertically generated ,ground reaction forces through the subject or standing foot ?
     
  2. efuller

    efuller MVP

    It's a little hard to figure out which leg you are referring to. Contralateral means other leg. In running, one leg is the contact leg and the contraleteral is the swing leg, except for the period of time when both legs are off the ground (double float phase).
     
  3. scotfoot

    scotfoot Active Member

    Hi Eric
    Lets say the right foot is in contact with the ground and the left foot and leg are in the air but swinging forwards . If timed properly can increased , vertical ground reaction forces ,produced by the right leg ,cause the left leg to accelerate forwards more quickly .
     
  4. efuller

    efuller MVP

    The leg bone is connected to the hip bone. So anything that causes the hip to accelerate forward is going to cause the swing leg to accelerate forward. Pure vertical force won't cause much horizontal acceleration. This is just a discussion of linear acceleration. That is just one meaning of the term accelerate forward. Another definition of move the leg forward is hip flexion, or rotation of the leg relative to the pelvis/trunk. An upward acceleration of the pelvis could have different effects depending on where the swing leg is relative to the trunk. When the swing leg is behind the trunk an upward acceleration will cause the leg to swing faster and when the swing leg is in front of the hip, upward acceleration of the pelvis will cause the swing leg to decelerate.
    Eric
     
  5. scotfoot

    scotfoot Active Member

    "Pure vertical force won't cause much horizontal acceleration " . I am not so sure . Purely vertical forces are one of the major factors in accelerating the arm/ hammer / body system in the hammer throw discipline . As the hammer descends the athlete applies great forces through the legs with both a rotational and vertical component and these forces cause the hammer to accelerate .

    So what I was getting at here was not about the was undoubted effect that the forward progression of the pelvis has on the swing leg during running but was instead about the effects of vertical displacement of the pelvis .

    Perhaps you could try the following thought experiment (please note that I am not advocating that anyone actually carries out this experiment for real or injury may result . )

    So the thought experiment involves the creation of a "third leg ". First you would put on a weights belt . To this you would attach an imaginary rope about three feet long with a ten kilo kettle bell tied to the end .(This is your third leg ) . Next step up onto two platforms which would be about two feet high and placed side by side but about a foot and a half apart .

    You should now have a metal picture of yourself with your left foot on one platfom ,your right foot on the other ,and the rope and weight dangling down into the space between the two .

    Now imagine an assistant giving the weight a push to start it moving backwards and fowards between your legs . Now .as the weight reaches its highest point behind you imagine bending your legs and ,as the weight falls apply force by straightening your legs . You would find that the weight rope system could be accelerated really quite quickly by the application of vertical forces through the feet and legs .

    So nothing new in any of that . However , I was recently standing on the inside of an athletics track when an international standard 400m runner came hurtling past . What surprised me was the height his hips reached as he ran . He must have been applying a lot vertical force to the track to get that high and I wondered if the mechanisms described above might not be in play with regard to forward progression of the swing leg .
     
  6. efuller

    efuller MVP

    I haven't thought that much about the physics of the hammer throw. But thinking about it now it is not so much the vertical forces, but the horizontal forces. When you look at a hammer thower, they are leaning away from the hammer. The hammer is pulling on the person and the person is pulling on the hammer. The person would accelerate toward the hammer unless there is some other force preventing that acceleration. That force is a horizontal force from the ground applied to feet of the person. At the ground foot interface there are both horizontal and vertical forces.

    To simulate how the person creates the angular velocity of the hammer, you need a string with a weight on the end. To make the weight spin you do have to pull on the string and keep changing the direction of pull so that the weight moves in a circle. There is a toy called an Alaskan yo-yo. (or so I was told it was called that) You have a string with weights on both ends. You grab the string in the middle and your goal is to try to get the weights swinging circularly in opposite directions. It is possible if you move your hand vertically. This illustrates the point that I made in my previous post. When you move the hip upwards vertically and the leg is behind the hip, the leg will accelerate forward. However, when the leg is in front of the hip, the leg will accelerate rearward with the same hip motion. This agrees with what you said about the timing of the forces.

    So, yes vertical motion of the pelvis could help swing the leg forward. However, there are emg studies that show the hip flexors become progressively more activated as running speed increases. The hip flexors are much more likely to be responsible, than vertical displacement of the pelvis, for swinging the leg forward.

    Additionally, look at running to see when those vertical forces would need to be applied. The stance leg becomes the trailing leg. The stance leg would have to provide the vertical lift to the pelvis to help initiate its own swing. My recollection is that running with less vertical displacement is more efficient than running with a lot of vertical displacement. Plantar flexion of the ankle could provide from some horizontal force that could help accelerate swing.

    Eric
     
  7. efuller

    efuller MVP

    Had to look it up after I posted

     
  8. scotfoot

    scotfoot Active Member

    Eric
    With regard to the mechanics of the hammer throw I have you at a bit of a disadvantage since I compete in this event all be it at a very modest level ( 6kg personal best 36 m a few months ago ) . During the throw the hammer goes through periods of acceleration and deceleration and the lifting action of the legs plays a huge role in developing ball speed .

    Love the video . These appeared in Glasgow primary schools about 40 years ago and were known as "clachers " . They were banned after cheaper versions started shattering and causing injury .

    You said
    "So, yes vertical motion of the pelvis could help swing the leg forward. However, there are emg studies that show the hip flexors become progressively more activated as running speed increases. The hip flexors are much more likely to be responsible, than vertical displacement of the pelvis, for swinging the leg forward. "

    So we are in agreement that vertical ground reaction forces in the standing leg can make a contribution to the forward travel of the swing leg . Which brings me to kicking footballs and rugby balls .

    Can increased vertical ground reaction forces in the standing foot help a player kick a ball harder ? The answer appears to be yes .

    Here is a quote from a relatively recent paper (1)

    "Therefore, accelerating the hip joint of the kicking leg in the vertical direction during the forward swing of the instep motion may be assumed to increase the swing velocity. Such hip acceleration is one of the technical elements that could be improved to increase ball velocity in female athletes."

    What mystifies me is why some researchers in this and related fields advocate progressive resistance training of the leg ,so that greater ground reaction forces can be generated ,without also advocating progressive resistance training of the intrinsic muscles of the foot . Surely foot strengthening would improve overall control ?



    (1)
    Comparison of Kicking Speed between Female and Male Soccer ...

    www.sciencedirect.com/science/article/pii/S187770581400527X
    by K Sakamoto - ‎2014 - ‎Cited by 3 - ‎Related articles
    A comparative study of the ball-kicking motion for the instep kick of female and ... As the verticaltranslational force increased during a forward swing, the swing ... Ground Reaction Forces and Kinematics of Plant Leg Position During Instep ...
     
    Last edited: Sep 2, 2017
  9. scotfoot

    scotfoot Active Member

    It has been shown that during a game of football ,the passing and shooting accuracy of players declines with fatigue . These are gross motor skills but both involve balancing on one foot ,which heavily recruits the intrinsic foot muscles . In my opinion , specific strengthening of these muscles may help preserve passing and shooting accuracy during a game of football .
    No point having the body of an Adonis but feet of clay .

    From the paper below -." These results suggest that the morphology of foot muscles plays an important role in balance performance, and that strengthening the intrinsic foot muscles may be an effective way to improve balance."

    Foot muscle morphology is related to center of pressure sway and ...

    https://www.ncbi.nlm.nih.gov/pubmed/28575753
    by X Zhang - ‎2017 - ‎Related articles
    Gait Posture. 2017 May 25;57:52-56. doi: 10.1016/j.gaitpost.2017.05.027. [Epub ahead of print]. Foot muscle morphology is related to center of pressure sway ...
     
  10. scotfoot

    scotfoot Active Member

    An interesting intrinsic foot muscle exercise video included on a FIFA web site .

    Treatment | FIFA Diploma in Football Medicine

    fifamedicinediploma.com/lessons/foot-treatment/The small intrinsic muscles of your feet (including the interossei and lumbricals) help stabilise an athletes foot and toes during movement. Intrinsic foot exercises .
     
  11. efuller

    efuller MVP

    The whole quote:
    Our results showed that larger abductor hallucis correlated to smaller COP sway, while larger peroneus muscles correlated to larger COP sway during single-leg standing. Larger abductor hallucis also benefited open-loop dynamic stability, as well as supported a more efficient transfer from open-loop to closed loop control mechanisms. These results suggest that the morphology of foot muscles plays an important role in balance performance, and that strengthening the intrinsic foot muscles may be an effective way to improve balance.

    There are other explanations that could explain the correlation seen in the findings. Different types of feet could be the reason. As an example STJ axis position. With a more lateral axis you would expect increased instability and increased peroneal size.

    Strengthening intrinsic foot muscles does not necessarily follow from the correlation that they found. From the correlation that they found you could also infer that weakening the peroneal muscles would improve balance.
     
  12. scotfoot

    scotfoot Active Member

    I agree that to identify whether a program of intrinsic foot muscle strengthening can improve passing and shooting in footballers , particularly in the second half of a game , a dedicated study would be required .
    However , the evidence shows that at least two of the intrinsic muscles of the foot are important to balance . Lack of use of these muscles , for example through bed rest , has been shown to result in their atrophy ( 24 % in three weeks in one study ) . It makes sense to me that if the intrinsic muscles are not in use for a period of time , perhaps due to injury , every attempt should be made to strengthen them prior to the player returning to action . ​
     
  13. efuller

    efuller MVP

    Or a gradual return to activity. Performing in the sport for limited time and / or limited intensity would be an excellent way to strengthen muscles.
     
  14. scotfoot

    scotfoot Active Member

    But would take longer .
     
  15. efuller

    efuller MVP

    Why do you think that?
     
  16. scotfoot

    scotfoot Active Member

    Fifa seem to think that specific strengthening exercises have a place in foot rehab (see above ). This is probably because such exercises have been used for the rehab of just about every part of the musculo skeletal system for centuries if not millenia .
    Leg break - cast, then supervised rehab including progressive resistance exercise .
    Ankle break or surgery -same , supervised rehab including strengthening using ,possibly ,therabands
    Following foot injury and intrinsic muscle atrophy ,shouldn't the same rehab prinsipals apply as apply to the rest of the body ?
     
  17. efuller

    efuller MVP

    We agree that participating in an activity that uses weakened muscles will strengthen those muscles. You said that it would take longer to strengthen those muscles if the injured athelete did a progressive return to their sport as opposed to progressive resistance training of individual muscles. Do you, or FIFA, have data on the length of time it takes to get to full strength with various activities?

    On the other hand...There are some rare injuries that are caused by weakness in a particular muscle. These patients can benefit from someone working with them to strengthen the specific weakened muscle.
     
  18. scotfoot

    scotfoot Active Member

    "You said that it would take longer to strengthen those muscles if the injured athelete did a progressive return to their sport as opposed to progressive resistance training of individual muscles. Do you, or FIFA, have data on the length of time it takes to get to full strength with various activities? "

    Data on this exists for skeletal muscles and it is a general principle in rehab that progressive resistance exercise produces an increase rate of muscle growth .
    What is it about the intrinsic muscles of the foot that makes you think they will react differently to progressive resistance exercise , than all the other skeletal muscles in the body ?
     
  19. efuller

    efuller MVP

    I didn't say that the intrinsic muscles of the foot would not respond progressive resistance exercise. What I am saying that a gradual return to activity will cause strengthening because it is exercise. My question is whether or not the muscles will strengthen faster if you go to the physical therapist, or if you just start working out on your own.
     
  20. scotfoot

    scotfoot Active Member

    If I could re-phrase your question too " does specific progressive resistance exercise strengthen atrophied intrinsic muscles more quickly than a progressive return to general exercise ?" In my opinion , all the indirect evidence would indicate that it does .
    The only specific data I can find relates to age related atrophy (sarcopenia ) and it appears that specific progressive resistance exercise is the ONLY way of strengthening the intrinsics in this case, since atrophy has occurred hand in hand with normal exercise .
    The question of muscles atrophied first by sarcopenia which is then exacerbated by disuse atrophy is obviously different to sarcopnia alone .However ,and again in my opinion , and given the importance of the intrinsic muscles to balance , it may be especially unwise to leave individuals in this category to their own devices .
     
  21. scotfoot

    scotfoot Active Member

    Sorry Eric , it's just occurring to me . Why would a person have to go to a physiotherapist for foot strengthening advice ? Why can a podiatrist not deliver this type of advice or treatment ?
     
  22. scotfoot

    scotfoot Active Member

    Eric
    With regard to muscle atrophy caused by bed rest , would it not make sense to maintain muscle mass and strength in the feet by resistance exercise during the period of bed rest ? In this way balance and gait would not impaired by intrinsic muscle strength deficits when the patient became active again .(obviously loss of intrinsic muscle strength is only one factor here )
    This type of approach ,prevention rather than cure , is the one adopted by NASA during manned space flight .
     
  23. efuller

    efuller MVP

    It depends on the reason for bed rest. For example if there was a navicular fracture you would want the person to not use their posterior tibial muscle, as use of the muscle could cause delayed healing of the fracture. But generally, maintaining strength, by any method, is a really good idea.
     
  24. scotfoot

    scotfoot Active Member

    After digging around a bit I came across this abstract which seems to indicate that although younger people may recover from disuse atrophy by "convention rehabilitation efforts " , an approach which uses resistance training is required to restore function in the elderly .
    Harder to find is information on the longer term effects of sarcopenia reversing , resistance exercise in the elderly . For example , can a six week resistance program produce a strengthening effect that lasts for a year or perhaps longer ? If yes , then Dr Karen Mickles work into reversing sarcopenia in the intrinsic foot muscles , becomes even more relevant .

    Quote from paper (1)

    "Importantly therefore, the present experiments demonstrate that resistance training is highly effective of increasing maximal muscle strength and neuromuscular function in elderly post-operative patients. Importantly, these increases in mechanical muscle function were accompanied by gains in muscle size, architecture and in the expression of IGF-I mRNA splice variants, resembling that typically seen in young healthy individuals when exposed to resistance training. In contrast, these positive adaptations could not be achieved with the use of neuromuscular electrical stimulation or conventional rehabilitation efforts alone. Collectively, these findings strongly underline the importance of implementing resistive exercises in future rehabilitation programs for elderly individuals. "

    Paper ref 1
    Dan Med J. 2017 Aug;64(8). pii: B5377.
    Plasticity and function of human skeletal muscle in relation to disuse and rehabilitation: Influence of ageing and surgery.

    Suetta C1.
     
  25. scotfoot

    scotfoot Active Member

    Of course muscle atrophy may be caused by inactivity related to pain during movement . Below are two quotes from a 2011 paper (1).
    To the best of my knowledge ,the subject of the study , the effects of resistance exercise in RA , have never been looked at in relation to the foot distal to the ankle joint .

    "Joint involvement in RA often leads to deformities and muscle atrophy, which dramatically affect RA management and outcomes. Specifically, impairment in range of motion and muscle strength increase RA-associated disability, widely impacting a patient's quality of life and leading to increased health-care costs, both for the patient and the health-care system. In addition, the decrease in joint mobility and muscle strength prevents RA patients from performing regular physical activities. Therefore, RA patients are often physically inactive [1], leading to further muscle deconditioning and exercise intolerance. "

    And
    "Resistance exercise in RA is safe, and the improvement in most outcomes was statistically significant and possibly clinically relevant for RA disability. "


    Paper (1)

    Efficacy of resistance exercises in rheumatoid arthritis: meta-analysis of randomized controlled trials

    Athan Baillet Mathieu Vaillant Michel Guinot Robert Juvin Philippe Gaudin
    Rheumatology, Volume 51, Issue 3, 1 March 2012, Pages 519–527,
     
  26. scotfoot

    scotfoot Active Member

    So looking at the two papers mentioned in the previous two posts it seems quite possible that the progression of sarcopenia in the feet of older adults might be far more severe where the subjects also suffer from RA related foot pain . Periods of pain during active phases of the disease will reduce activity , leading to intrinsic foot muscle atrophy which is not then fully restored during quiescent periods .
    The authors of both papers recommend progressive resistance exercise for treating the respective conditions of muscle atrophy in older people and in cases of RA ,although they do not mention the foot specifically .
    You have to wonder though , at the potential size of the benefits that this form of exercise would have on the foot and general health of individuals with both sarcopenia and RA .
     
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