Have you ever wondered why people who walk together quickly synchronize their gaits ?

From healthy heart cells that synchronize to a single beat, to women in school dormitories or work places who synchronize their menstrual cycles, to fireflies who begin blinking in synchrony when they all perch in the same tree synchronization is something that is abundant in nature.  
It is no wonder that we find synchronicity in one of our most primitive and frequent motor patterns, walking together with someone shows the same synchronicity phenomenon.

Hold the hand of your favorite person and go for a walk. Within a few strides your gaits will synchronize. Is it because it is easier ? Is it because when synchronized the arm swings will match thus making it easier and more effortless to hold hands ?  Does the same effect occur 
if you are not holding hands ? Studies have concluded that although it does not happen all of the time, they found it occurs in almost 50% of the walking trials even among couples who do not usually walk together. This is far too high a percentage to not make it a statistically significant finding.

The synchronization between walking partners is more complex than it seems on the surface.  There are two types of synchronization, in-phase (both person’s right foot move forward at the same time) and out-of-phasesynchronization (where the right foot moves forward with the partners left foot).  You can see in the video above that the couple has subconsciously fallen into an Out-of-Phase synchronization, then after the tide splash that throws them off within just a few steps they fall right back into Out-of-Phase synchronization and hold it in that state.  There are multiple factors and communication mechanisms occurring. There are auditory mechanisms in play such as the sound of the other persons foot fall.  There are even visual mechanisms through peripherally seeing your partners arm swing and foot fall which encourages the imitation synchronization. However, the strongest in-phase synchrony occurred in the presence of tactile feedback meaning hand holding or embracing each others waist from behind, which couples often do when walking more slowly, seem to create a stronger synchrony.  When this tactile component is engaged between two walkers it is plausible that the upper and lower limbs move more freely when paired up, particularly with arm swing.

What is thought to happen is that one partner dominates the lead in the gait, just as in dancing, one person is the leader and the other is the follower. The lead partner’s lower limbs determine the movement of their arms, which in turn when holding hands, sets the arm movement pattern in the partner then determining the leg swing and stance phases. Thus, synchrony is achieved. 

However, it is important to note that many of the studies were clear to mention that even in non-tactile cases, many of the gaits of two people walking together are synchronized. This was likely due to the visual and auditory parameters however height, leg length cadence etc could also play into those successful non-tactile synchrony cases.

These are interesting findings at 50% because it is very unlikely that any two people are of the same height, leg length, cadence, stride and step length.  These are all parameters that are likely to change the likelihood of gait synchrony.  Zivotofsky found that “even in the absence of visual or auditory communication, couples also frequently walked in synchrony while 180 degrees out-of-phase, likely using different feedback mechanisms”. The studies below discuss many issues of this synchrony but it is perhaps most significant in clinical rehabilitation cases or in early or moderately advanced movement impairment disorders and diseases these findings may partially explain how patients can enhance their gait function when they walk with a partner or therapist.  It is in these movement impairment syndromes and diseases where the central processing and Central Pattern Generators (CPG’s) are diseased leaving them with the need for other cues such as those discussed here today, auditory, visual and tactile.  

You may have read our previous blog articles on arm swing and how intimately they are anti-phasically (opposite) paired with lower limb swing.  But today’s blog post article took limb swing to another level.  Stay tuned for more on arm and leg swing in human movement.  If you wish to read our other works on arm and leg swing and their deeper effects on gait, go to our blog www.thegaitguys.tumblr.com and enter the words “arm swing” into the SEARCH box

Shawn and Ivo…….. taking gait far beyond what you learned about it in school.

References used:

J Neuroengineering Rehabil. 
2007; 4: 28. The sensory feedback mechanisms enabling couples to walk synchronously. An initial investigation.  Ari Z Zivotofsky and Jeffrey M Hausdorff  Published online 2007 August 8. doi:  10.1186/1743-0003-4-28

Hum Mov Sci. 2012 Jun 22. [Epub ahead of print] Modality-specific communication enabling gait synchronization during over-ground side-by-side walking. Zivotofsky AZ, Gruendlinger LHausdorff JM.Gonda Brain Research Center, Bar-Ilan University, Ramat-Gan 52900, Israel.