Dear Tayebeh, 

Not involved in labaratory analysis of gait, but involved in the ( Public Health) research by observation on how the increasing amount of spinal problems in de sedentary youth is evolving, I can give you some clues as an experienced orthopedic surgeon.

variation of gait is completely dependant on the development of optimal alignement of the spine during growth. Intrinsic problems of the CNS or muscles ( e.g. CP, Duchenne etc) can give postural deviations and abnormal gaitpatterns easily, as we know. But in healthy children the lack of free playing , lack of extension excersises, and the incredible amount of hours sitting and slumping gives a myraid on spinal problems and altered gait patterns. Most sport don't meet the great positive influence the "old"orthopedic schoolgymnastics gave to the healthy development of strenght, balance properties  and full ROM to give healthy gaitpatterns. 

This suboptimalisation ( instead of "variation") is due tot the lack of stretch growth of the CNS , whilst the skeleton grows tremendously in children ( especially where there is a surplus on food and Proteins as in western countries, and they don't use is for mobility). 

In order to understand gait patterns the individual posture, the individual laxity of joints and ligaments, and the individual , but secondary thightness of the neuromusculair structures should be assesed.  

With the "Gameboyback", an early kyphosis at the thoracolumbar joint you  can find in all cases thight hamstrings, tight calves (SLR test) . In the Scheurmann you can asses this the most easily. 

Because no research is ever done on this combined patho-anatomical and patho physiological co-existence , what always must lead to "abnormal"gait patterns ( exo in hips, varus in knees, short stance phases, sometimes toewalking in younger kids), I can only refer to old german books on schoolgymnastics, schoolstudies on postures out of the era before 1940, when this knowledge was still well estabished in Orthopedics and general population. You can find some articles of me where I did some steps to get this knowledge back, focussed around the brilliant observations and research the Csech neuroradiologist Milan Roth did on the "neuro-osseous growth relations during growth. Not only in scoliosis, but every child grows according to this tension steered systematically growth of the complete body. 

Good luck with an attempt to implicate this in your studies. 

Piet van Loon

During postural control tasks you typically have no discrete timing events that can be easily detected such as stance or swing (largely determined by force platforms or foot switches).  Typically we have a synch cable (common input signal) to synchronize, center of pressure measures with EMG.  Usually, this is a pulse wave from a foot switch that can be used to match up your data.

Dear Tayebeh, if you have a Apple device, you should test the Sway App. It's a very interesting app to mensure balance control, and have international validation with pappers! Enjoy!

Dear Piet,

 Thank you very much for your great comment.

But my purpose of "event detection" in the process of quiet standing was in adults who have CNS problems. I wonder whether, as a researcher and consultant orthopedic surgeon, you have an ofer about diagnosis of muscular events at the quiet standing? Are there any standard physiologic conditions (in muscle activities) for calf muscles and tibialis anterior at the quiet standing? 

Regards,

Tayebeh Jahani.

Dear Thomas,

   Thank you so much for your great answer.

Alright, I recorded EMG from calf muscles and tibialis anterior while subject sway in a small angle from vertical. Then we are going to define some criteria as events during the standig. But I don't know how we can define these criteria? Are there any standard physiologic conditions (in muscle activities) for calf muscles and tibialis anterior at the quiet standing?

Regards,

Tayebeh Jahani 

Dear Filipe,

   I have an Android device . Is this app for Android devices? Is "Sway" the app name?

Tayebeh,

Do you have a experimental perturbation to their stance?  There are many papers about having a perturbation introduced (visual field moves or there is some other standardized "push" or "pull" on the participant).  If you know when this happens (because this is synchronized with your data), you can measure what is the effect based on this event.  Otherwise, if they are just standing there you can report center of pressure variables (sway area, a/p or m/l sway excursion, velocity or others).  In standing maybe just integrated or peak emg or co-contraction ratio over a set time may be appropriate.

Good luck,

Tom

Tom,

  Great idea. thank you. So we applied one perturbation with pushing forward and backward the subject from hip, and the subject standing on a force plate without any support. then she should try to be balance by co-contraction her ankle muscles as it possible. So our recorded data show this contractions (peak EMG or deviation angle, AP/ML sway excursion as you said just at the moment of perturbation). Now can we import this data to a chaotic or fuzzy Hidden Markov Model to estimate the hidden states of EMG as a model for clustering the data that identify what events are more important in balance control in normal subject. After that we'll try to design a controller for persons have CNS problems that they can not control their balance in upright standing( such MS patients or post stroke, etc). Do you have any idea about outputs of HMM? Basically can this experimentation predict normal dynamic patterns in healthy subject to design a controller for patients?

Dear Tayebeh, 

Stance and locomotion based from a normal stance are dependant of the functional and morphological conditions of the spine ( posture, springlike function, mobility) In bad postures there is a reversed pattern of movements. 

I think the knowledge on balance as wrote down by Vladimir Landa is leading tot undestand what happens an dyou have to assess what you measure in EMG etc. 

If ( by sitting) the thoracolumbar spine is part of a kyphosis or kyphotic by itself and not part of a mobile long upgoing lordosis ( like in Beyonce or belly or ice dancers) the action patterns instigated first by the core- muscles will be reversed or pathological. 

Greetings Piet van Loon

Dear Piet,

   Tank you for your intresting comment