How robust is human gait to muscle weakness?→

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Below you will find a link for the 2012 article in Gait Posture entitled “ How Robust is Human Gait to Muscle Weakness?”
Today’s Take Home Points are:
  1. Proper technical form in walking and running is critical. Everyone talks about it at the ground level assuming we are all idiots.  No one is getting down to the roots of the problems and solutions like we try to do.  This means reducing Cross Over gait pathologies which we have shown you previously. 
  2. Attempt to maintain clean movement patterns free from compensations. For one,  make sure you have sufficient ankle rocker (dorsiflexion bend). 
  3. Make sure your abdominal muscles and core are symmetrical and strong. Obliques are key but not exclusively so.  They will make sure that your initial hip flexion comes from them and not the hip flexors !
  4. Do your glute work to ensure your glutes are in charge of hip extension and not your quadriceps.
  5. Make sure you are not a victim of compensations such as overactive hip flexors, weak hip abductors and premature calf engagement.

Now, lets get into the details, this summary is pretty soft.

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We are ordering this article to see its specifics so stay tuned for any other info. Here we dissect the articles main principles to put it into terms that might serve you well as a walking or running human.
Lets start with a great quote from Basmajian in Muscles Alive,
Locomotion is “the translation of the center of gravity through space along a path requiring the least expenditure of energy. Pathologic gait may be viewed as an attempt to preserve as low a level of energy consumption as possible by exaggerations of the motions of the unaffected levels. When a person loses one of the six determinants of human gait compensation is reasonably effective. Loss of two determinants makes effective compensation impossible; the cost in terms of energy consumption triples adn apparently discourages the patient to the point of his admitting defeat."  Basmajian, 1953, Muscles Alive: Their Functions Revealed by Electromyography.  (Yes, it is 60 year old statement, but we use this book all the time because it is one of a kind and this guy was ahead of his time. His information is frighteningly accurate even on today’s research terms.)
What this article seems to indicate is that weakness in certain muscles has some predictors.  The article inquires, "how much weakness can be tolerated before normal daily activities become impaired?” In theory what they were looking at was a simple principle suggesting that there is a kind of tipping point for muscle weakness before there is sufficient weakness to require a gait compensation pattern to protect the joints and attempt to preserve the motion of gait. 
What the study found is that the muscles of hip extensors and knee extensors (glutes and quadriceps are assumed here) are particularly robust and resist weaknesses. These are sagittal (forward progression) muscles and are quite necessary for gait and running movement. 
In contrast the study indicated that gait is most sensitive to weakness of plantarflexors, hip abductors, and hip flexors.
So, how might this be interpreted ?  Well, lets start with the hip abductors. These are the gluteus medius muscles for the sake of generality.  These protect the frontal plane and help keep the pelvis neutral. They protect you from the Cross Over gait we have talked about over and over again in previous blog posts and YouTube videos.  Without proper frontal plane stability gait pathologies arise (not to say this is the only source however).
Now lets talk about the hip flexors. This muscle group is every therapists gem to talk about. There always seems to be a runner or patient talking about how their massage therapist,physical therapist or athletic trainer has told them that their hip flexors are tight, weak or filled with trigger points.  We do not dispute their findings here. But what we wish for you is to use logic based on THE FACTS. Most of these people will be alarmed to find out that a main function of the hip flexors is not to initiate hip flexion.  NO ! Say it ain’t so Jack !  Well the truth is that the psoas  muscles are in a big way hip flexor PERPETUATORS, not INITIATORS.  The abdominal muscles are the first muscles to initiate hip flexion via derotating the obliqued pelvis at heel rise.  It is only once the pelvis is moving forward with the pendulum leg following forward that the hip flexors engage to perpetuate the limb flexion at the hip.  Remember, once the leg is in swing phase much of the hip flexion movement is PASSIVE from momentum ! (We will save you from another Newton’s Law diatribe here).  So, it might be safe to say that whatever “your people” are finding are results and consequences to impaired use of the core to INITIATE proper limb/hip flexion. According to this journal source: “Psoas major works phasically: (1) as an erector of the lumbar vertebral column, as well as a stabilizer of the femoral head in the acetabulum at 0 -15 degrees flexion at the hip joint; (2) less as a stabilizer, in contrast to maintaining its erector action, at 15 -45 degrees; and (3) as an effective flexor of the lower extremity, at 45 -60 degrees."  This study seems to support that the psoas is not an initiator of hip flexion, rather it engages at 45 degrees making it a clear perpetuator.
Now lets dialogue briefly on the plantarflexors assuming they mean the gastrocsoleus complex.  All we are willing to say here (because this is a project we are working on) is that when the gastrocsoleus are not used correctly to drive forward progression they may serve to lift the person (this comes with premature heel rise and thus premature calf firing). This can lock out further ankle dorsiflexion range and thus hip extension range. Thus, limiting the ability to gain a sufficient hip extension-pelvic rotation to enable sufficient range for the abdominals to serve as hip flexor initiators and possibly calling on the psoas and other hip flexors to prematurely engage to initiate the motion. 
How do we summarize this article ?  The journal abstract did it nicely for us. "Compensations are generally inefficient, and generate unbalanced joint moments that require compensatory activation in yet other muscles. As a result, total muscle activation increases with weakness as does the cost of walking.” And it will go as well for running in our opinion.
Again, the Take Home Points are:
  1. Proper technical form in walking and running is critical. Everyone talks about it at the ground level assuming we are all idiots.  No one is getting down to the roots of the problems and solutions like we try to do.  This means reducing Cross Over gait pathologies which we have shown you previously. 
  2. Maintain clean movement patterns free from compensations. Thus, make sure you have sufficient ankle rocker (dorsiflexion bend). 
  3. Make sure your  abdominal muscles and core are symmetrical and strong. Obliques are key but not exclusively so.  They will make sure that your initial hip flexion comes from them and not the hip flexors !
  4. Do your glute work to ensure your glutes are in charge of hip extension and not your quadriceps.
  5. Make sure you are not a victim of compensations such as overactive hip flexors, weak hip abductors and premature calf engagement.

Who are we ? Shawn and Ivo, The Gait Guys. Two doctors dedicated to challenging the myths and lies out there in the world and on the internet on gait and running from the perspectives of orthopedics, neurology and biomechanics. 

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Gait Posture. 2012 Feb 29. [Epub ahead of print]

How robust is human gait to muscle weakness?

van der Krogt MM, Delp SL, Schwartz MH.

Source

Department of Rehabilitation Medicine, Research Institute MOVE, VU University Medical Center, Amsterdam, The Netherlands; Department of Biomechanical Engineering, University of Twente, Enschede, The Netherlands.

Abstract

Humans have a remarkable capacity to perform complex movements requiring agility, timing, and strength. Disuse, aging, and disease can lead to a loss of muscle strength, which frequently limits the performance of motor tasks. It is unknown, however, how much weakness can be tolerated before normal daily activities become impaired. This study examines the extent to which lower limb muscles can be weakened before normal walking is affected. We developed muscle-driven simulations of normal walking and then progressively weakened all major muscle groups, one at the time and simultaneously, to evaluate how much weakness could be tolerated before execution of normal gait became impossible. We further examined the compensations that arose as a result of weakening muscles. Our simulations revealed that normal walking is remarkably robust to weakness of some muscles but sensitive to weakness of others. Gait appears most robust to weakness of hip and knee extensors, which can tolerate weakness well and without a substantial increase in muscle stress. In contrast, gait is most sensitive to weakness of plantarflexors, hip abductors, and hip flexors. Weakness of individual muscles results in increased activation of the weak muscle, and in compensatory activation of other muscles. These compensations are generally inefficient, and generate unbalanced joint moments that require compensatory activation in yet other muscles. As a result, total muscle activation increases with weakness as does the cost of walking. By clarifying which muscles are critical to maintaining normal gait, our results provide important insights for developing therapies to prevent or improve gait pathology.