Dietz (2002). Do human bipeds use quadrupedal coordination?

[Wise Young]

• Dietz V (2002). Do human bipeds use quadrupedal coordination? Trends Neurosci. 25 (9): 462. Summary: Tackling the question of whether control of human gait is based on that of a quadrupedal locomotion system is of basic and practical relevance. During evolution, the increased influence of a direct cortical-motoneuronal system in parallel with more specialized hand function might have replaced phylogenetically older systems that organized locomotor movements. However, recent research indicates that interlimb coordination during human locomotion is organized in a similar way to that in the cat. Hence, it is hypothesized that during locomotion, corticospinal excitation of upper limb motoneurons is mediated indirectly, via propriospinal neurons in the cervical spinal cord. This allows a task-dependent neuronal linkage of cervical and thoraco-lumbar propriospinal circuits controlling leg and arm movements during human locomotor activities. The persistence of such movement control has consequences for rehabilitation and the applicability of animal research to human patients with spinal cord injury. ParaCare, Institute for Rehabilitation and Research, University Hospital Balgrist, Forchstr 340, 8008, Zurich, Switzerland.

[Arturo]

I presume all the subjects were walking on a treadmill with varying velocities. I suspect that the results will be perfectly usable for this reference. When paralysis or tissue damage occurs, abnormal gait is the result. It is interesting to note, by the way, that there
are two different swinging modes, dependent on walking speed. It is also
well known, that counter rotation of the upper trunk is necessary to keep
balance; obviously, swinging arms amplify this balancing motion pattern. Is there a connection between the neural circuitry that activates arm swing and circuitry that activates the legs while walking? In the cat, interlimb coordination has been attributed to long intersegmental propriospinal circuits, which are long spinal nerves. I would assume arm posture affects lower limb reflex while walking in individuals with incomplete spinal cord injury. In my opinion, locomotion therapy for incomplete SCI is more beneficial when armswing is included as compared to assisted devices.

[Wise Young]

Arturo, great point. This is a subject of some discussion at the meetings that I have been to in the past 6 months. Many of the locomotion people are indeed thinking about entraining quadripedal locomotion rather than bipedal locomotion. The hierarchy of reflex activation, according to Sir Charles Sherrington (http://www.nobel.se/medicine/laureates/1932/sherrington-bio.html), goes in the following order:
1. Stretch reflex. This is where stretching of a muscle causes sensory input into the spinal cord that causes the muscle to contract. This monosynaptic reflex is mediated by spindle receptors that maintain the position of muscles.
2. Extension reflex. This is when the leg is extended so that the quadriceps activation is associated with gastrocnemius. This is what allows you to stand.
3. Flexion reflex. This is where a cutaneous stimulus causes the arm or leg to go into flexion. This is the classic withdrawal reflex. Unlike the stretch reflex, this involves multiple muscles on one side.
3. Cross extensor reflex. This is when a flexion reflex occurs on one side, the contralateral side goes into extension. This is what allows you to balance with your other when one leg is flexed.
4. Reciprocal reflexes. This is of course when the legs are stepping alternatively with swing-stance modes.
5. Quadripedal reflexes. This is where the arm swing comes in and the forelimb movements are coordinated with the legs.
6. Brainstem-spinal reflexes. Many of the reflexes require some brainstem involvement. For example, when you brush the dorsal surface of a rat's foot, it will make a stepping motion (like you would stepping over a tree branch).

Most of the locomotor functions are coordinated through a network of neurons situated in the L2 spinal cord, sometimes called the central pattern generator. The CPG coordinates the left and right sides, as well as multiple segments, of the spinal cord. Although the CPG have been demonstrated in most vertebrate animals, the location and function of the CPG in humans was controversial until recently. Hermann and Dimitrijevic separtely showed that this center at the L2 spinal cord not only can initiate locomotion but will recruit many of the muscles that are not under direct voluntary control, thereby greatly improving the efficiency and coordination of locomotor function. I believe that L2 stimulation will be a very important part of locomotor training.

Wise.

[Arturo]

Thanks for your words of wisdom...locomotion therapist should entrain quadripedal locomotion rather than bipedal locomotion depending on the patient's ability. In incomplete paraplegia patients, reciprocal movement is disturbed in two extremities, by shortened excursion of the each flexors and extensors in each extremity. IF reciprocal movements of the flexors and extensors are disturbed, propulsive flexion-extension movement in each joint of the extremity is inhibited. What do you think about applying a small amount of reciprocating FES to the knee extensors and flexors during the stance and swing gait like movements in locomotion therapy? Do you think this would enhance or send an additional message to the L2 stimulation? In the case of hemiparesis, the reciprocating FES could be applied to the weak side of the body during locomotion therapy to enhance or send an additional message to the CPG. Maybe the reciprocating FES to the knee extensors and flexors would give the patient a little bit of help in the beginning of locomotion therapy. Of course, the 4 channel reciprocating FES would have to be properly incorporated into the symmetrical repetitive gait movements. I understand this type of therapy is not for everyone on this forum. I wouldn't want to raise false hopes for people with complete spinal cord injuries.

[Wise Young]

Arturo,

I agree very much with the approach that you are suggesting. At the present, much of the strategy of FES stimulation is directed towards "controlling" movement rather than facilitating movement. Because reciprocal inhibition is one of the strongest and tightest linked of the reflexes, it stands to reason that one of the ways in which one can obtain relaxation of a spastic muscle is to stimulate the antagonist muscle.

The interesting aspect of the CPG stimulation is that one can use lower intensity stimulation to reduce the activation threshold for locomotor programs. For people who have reduced numbers of axons getting to the lower cord and who have to consciously focus on getting locomotor patterns going, such stimulation will not only recruit more muscles into the locomotor behavior but allow people to have a more normal locomotor activation.

There is now a new and exciting class of stimulators coming out made by the Alfred Mann Foundation/Institute (http://www.usc.edu/dept/engineering/CNE/mann/). These are wireless stimulators, using rice-grain size electrodes that are powered by radio waves and can both stimulate and record. I am hoping that this technology can be used to facilitate locomotor training of people. It should be relatively non-invasive.

Wise.

[Arturo]

I concur with your opinion, recruiting more muscle activity into the locomotion therapy will allow people to have a more normal locomotor activation. Passive movement does not help, either active movement an or patterns need to be trained actively. Quadripedal reflexes during locomotion therapy will also recruit more activity for a more normal locomotor activation.

[This message was edited by Arturo on Sep 01, 2002 at 08:46 PM.]

[kirtley]

Dear all,

Arturo invited me to comment. I stress that I have no experience in PWB therapy, although my colleague at Catholic University has a Lokomat.

It does strike me from a biomechanial point of view that there are some fundamental problems. The key requirements of gait are as follows:

1. Stance support
2. Swing initiation
3. Forward progression

It seems to me that pretty much all that PWB therapy offers is #2. You are still left with the problem of how to support the body, and how to move it forward over the advanced limb. Of course, you can do all of this with crutches, and for a while I'm sure many people will be get their hopes raised, much the way they were in the '80s by FES. But 4-point gait in this manner is extraordinarily fatiguing, and I don't think it will ever offer much more than an exercise option.

Chris

[Arturo]

I understand your colleague Joseph Hidler PhD has paraplegia. I wonder if Joe Hidler is on our forum?

Thanks for your comments regarding partial weight bearing. I understand your colleague Joseph Hidler PhD, is principle investigator for studies involving the Lokomat at The National Rehabilitation Hospital and assistant professor in Biomedical Engineering Department at the Catholic University of America. Joseph is doing a clinical study to investigate the benefits of robotic-assisted gait training in helping to restore gait in stroke and SCI patients. In addition to conducting studies using the Lokomat robotic treadmill, the ANBL team is planning a number of research studies aimed at advancing the diagnosis and treatment of neuromuscular pathologies. The studies examine changes in muscle properties after spinal cord injury, investigate weakness in the paretic leg of people with stroke, and track cortical reorganization using functional magnetic resonance imaging in people with stroke in order to correlate changes in brain activity with deficits and recovery of motor function. Chris, I've enjoyed reading one of your web sites:

http://guardian.curtin.edu.au/cga/

I would be interested in following up with Joe Hidler's clinical studies in helping to restore gait in stroke and SCI patients. http://www.hocoma.ch/engl/lokomat_movie.html


Best Regards,
Arthur

[Arturo]

From the "rules of spinal locomotion" (see A. Wernig, Paraplegia 30, 1992) a
"normal" gait pattern may be implied. To me "normal" includes of course
movement of arms as well as of trunk and shoulders and even the head
position (a normal gait pattern does not occur if you walk while looking
down on your feet e.g.). It is good if Volker Dietz postulates a scientific
explanation. But practice shows that gait training including arm swinging in
many cases is just impossible, either due to knee or trunk instability or
anxiety or many other reasons. Patients who are not able to walk
"normally" are told to use the bars mainly for balance which still allows a
loose movement of the shoulder, elbow, and ankles. If the patient has the impression
of progress, the therapist may start holding their hand and by moving the patients hand in the right direction and rhythm arm swinging is imitated and initiated. Using a mirror
to enable a patient to watch what he is doing and to avoid any tendency
looking down on the feet. Wernig also includes the capacity of imagination. If you
imagine a perfect gait your body will follow as much as possible. This
method is successfully used in many sports and in QiGong, a branch of TCM.

[Scientific devil's advocate]

[QUOTE]Originally posted by Wise Young:


6. Brainstem-spinal reflexes. Many of the reflexes require some brainstem involvement. For example, when you brush the dorsal surface of a rat's foot, it will make a stepping motion (like you would stepping over a tree branch).

*************************

Wise, this is an interesting post. What is the name of this reflex? I'd like to do some reading on it..... can you recommend a reference supporting the idea this reflex is mediated via the brainstem (do spinalized animals exhibit this reflex?)
Thanks

[Arturo]

Since you mailed me Dr. Kirthleys statement let me give you a few comments:
the way we use partial weight support and walking on the treadmill (in
incomplete! paralyses) seems to have different aspects. It enables the
patients to learn to bear full body weight and to stand and to make forward
progression on the ground. Success requires motivated (!) patients and
skilled therapists. We start with very low speed (0,2 km in the average) to
enable the patients to perform the different gait elements correctly and to
walk as actively as possible. (Some time ago I saw a video record of Mr.
Reeves` treadmill training in TV and was shocked by the speed that was
used.) At the beginning in most cases two therapists move the legs.
According to the increasing ability of the patient we increase body weight
up to full load and increase speed but only to a degree the patient is able
to move his legs on his own - using the harness finally only for security.
As soon as possible we start to "translate" the achievements on the
treadmill into walking on the ground. In case of Paraplegia our patients
should be able to go home and use a walker in every day life for shorter
distances. (Walking with crutches implies more shifting body weight on the
arms and is certainly fatiguing.) My experience tells me that there is much
lower progress in patients not able to concentrate or suffering depression -
that leads to overall passivity and mechanical character of the training
method. I can hardly imagine that robotic devices are of great help
regarding increase of walking capability though they may certainly be
reasonable to avoid muscle atrophy, keep the blood circuit going etc.