The Fudge Factor

image credit:,_April_2008_cropped.jpg

image credit:,_April_2008_cropped.jpg

We know from experience that it is often easier to accomplish a task faster, rather than slower (like an exercise or skiing) because of the cortex “interpolating” or making its “best guess” as to what (based on past experience) is going to happen and in what order. There is a certain amount of guess work (or what we call “the fudge factor”) involved.

Walking at a slower speed (or performing an exercise at a slower speed for that matter) has increased muscular demands, than doing it more quickly. Here is one study that exemplifies that.

“These findings may reflect a relatively higher than expected demand for peroneus longus and tibialis posterior to assist with medio-lateral foot stability at very slow speeds”

Here, they thought muscular demands would be proportional to speed, increasing with increasing demands. Like many things, what we think is going to happen and what actually happens can be 2 different things : )

Dr Ivo Waerlop, one of The Gait Guys

#fudgefactor #corticalinterpolation #muscledemands #gait #gaitguys

Gait Posture. 2014 Apr;39(4):1080-5. doi: 10.1016/j.gaitpost.2014.01.018. Epub 2014 Feb 6.

Electromyographic patterns of tibialis posterior and related muscles when walking at different speeds.

Murley GS1, Menz HB2, Landorf KB2.


Things may not always be how they appear.

What can you notice about all these kids that you may not have noticed before?

Look north for a moment. What do you notice about all the kids with a head tilt? We are talking about girl in pink on viewers left, gentleman in red 2nd from left, blue shirt all the way on viewers right. Notice how the posture of the 2 on the left are very similar and the one on the right is the mirror image?

What can be said about the rest of their body posture? Can you see how the body is trying to move so that the eyes can be parallel with the horizon? This is part of a vestibulo cerebellar reflex. The system is designed to try and keep the eyes parallel with the horizon. The semicircular canals (see above), located medial to your ears, sense linear and angular acceleration. These structures feed head position information to the cerebellum which then forwards it to the vestibular nucleii, which sends messages down the vestibulo spinal tract and up the medial longitudinal fasiculus to adjust the body position and eye position accordingly. 

Can you see how when we add another parameter to the postural position (in this case, running; yes, it may be staged, but the reflex persists despite that. Neurology does not lie), that there can be a compensation that you may not have expected?

What if one of these 3 (or all three) kids had neck pain. Can you see how it may not be coming from the neck. What do you think happens with cortical (re)mapping over many years of a compensation like this? Hmmm. Makes you think, eh?

Ivo and Shawn. The Gait Guys. Taking you a little further down the rabbit hole, each and every post.

Arm Swing Matters !

Arm swing matters! “The data thus suggest that the motor cortex makes an active contribution, through the corticospinal tract, to the ongoing EMG activity in arm muscles during walking.” Appropriate afferent feedback loops (from the joints in the upper and lower extremities) are necessary for the brain to run this motor engram; so if gait is altered, so are those feedback loops. You are witnessing a CORTICAL phenomenon! It’s about a lot more than pronation!

get the article !!!

J Physiol. 2010 Mar 15;588(Pt 6):967-79. Epub 2010 Feb 1.

Corticospinal contribution to arm muscle activity during human walking.

Barthelemy D, Nielsen JB.


Department of Exercise and Sport Science, University of Copenhagen, Blegdamsvej 3, DK-2200 Copenhagen, Denmark.


When we walk, our arm muscles show rhythmic activity suggesting that the central nervous system contributes to the swing of the arms. The purpose of the present study was to investigate whether corticospinal drive plays a role in the control of arm muscle activity during human walking. Motor evoked potentials (MEPs) elicited in the posterior deltoid muscle (PD) by transcranial magnetic stimulation (TMS) were modulated during the gait cycle in parallel with changes in the background EMG activity. There was no significant difference in the size of the MEPs at a comparable level of background EMG during walking and during static PD contraction. Short latency intracortical inhibition (SICI; 2 ms interval) studied by paired-pulse TMS was diminished during bursts of PD EMG activity. This could not be explained only by changes in background EMG activity and/or control MEP size, since SICI showed no correlation to the level of background EMG activity during static PD contraction. Finally, TMS at intensity below the threshold for activation of corticospinal tract fibres elicited a suppression of the PD EMG activity during walking. Since TMS at this intensity is likely to only activate intracortical inhibitory interneurones, the suppression is in all likelihood caused by removal of a corticospinal contribution to the ongoing EMG activity. The data thus suggest that the motor cortex makes an active contribution, through the corticospinal tract, to the ongoing EMG activity in arm muscles during walking.