Human gait is cyclical. For the most part, when one limb is engaged on the ground (stance phase), the other is in swing phase (in walking gait there is a brief period of double limb support), then the limbs switch tasks. For us to move cleanly and efficiently one would assume that the best way to do that would be to ensure that both limbs are capable of doing the exact same things, with the same timing, same skill, same endurance and same strength. For this clean seamless motor function, one must assume that there is complete limb symmetry (length, long bone torsion, the same rate and degree of pronation, supination, ankle dorsiflexion, hip internal/external rotation, same strength, power output etc) and one would hope there would be no injuries that had left a remnant mark on one limb thus encouraging a necessary compensation pattern in that limb (and one that would then have to be negotiated with the opposite limb). For example, when right ankle rocker (dorsiflexion) is impaired, early heel departure will occur and hip extension will be limited. An alteration in right glute function will follow. One could theorize that the left step length (the length of measure from right heel strike through to left heel strike) would be shortened. This would cause a premature load onto the left limb, and could very well force the left frontal plane to be more engaged than is desirable. This could lead to left core and hip frontal plane weakness and compensation patterns to be generated. To complicate the cyclical scenario, the time usually used to move sagittally will be partially used to move into, and back out of, the left frontal plane. This will necessitate some abbreviations in the left stance phase’s timely mechanical events. Some biomechanical events will have to be abbreviated or sped through and then the right limb will have to adapt to those changes. These are simple gait problems we have talked about over and over again here on the gait guys blog. These compensation patterns will include weaknesses as part of the pattern, and fixing those weaknesses does not address the right ankle rocker problem. Fixing said weaknesses merely encourages the brain to possibly continue to perpetuate necessary tightnesses in other muscles and motor linkages and engrain the compensations further or more complexly. It is easy to find something weak, it takes a sharp brain to find the sometimes silent sparking event underneath it all. One’s focused task should be, are you able to find the problem in this never ending loop of compensations and find a way to unwrinkle the system one logical piece at a time, or will you just chose to strengthen the wrinkled system and hope that the new strength on top of the compensations is adequate for you our your client ? One should not have to do daily or weekly rehabilitative sessions and homework to negate and alleviate symptoms, this is a far more durable machine than one that needs daily support. Rather, one that “seems” to need daily supportive homework/rehab is one that likely needs the underlying limitation to be uncovered. However, there are always exceptions. If one has a fixed issue, for example Foot Baller’s Ankle, then regular doses of lower limb anterior compartment work may be necessary to ensure that further ankle dorsiflexion range is not eroded.
Now, lets add another wrinkle to the system. What if there were problems before any injuries ? Meaning, what if there were problems during the timely maturation and suppression of the primitive reflexes ? Or problems in the timely appearance or maturation of postural reflexes? A problem in these areas may very well result in a central or peripheral nervous system malfunction and a representation of such in one’s movement and gait. But, that is a discussion for another time.
Shawn and Ivo, the gait guys
photo: courtesy of Thomas Michaud, from the excellent textbook, Human Locomotion
We get a lot of interest in our posts on stretching. Seems like this is a pretty hot subject and there is a lot of debate as to whether it is injury preventative or not. Are you trying to physically lengthen the muscle or are you trying to merely bring it to its physiological limit? There’s a big difference in what you need to do to accomplish each of these goals. Lets take a look at each, but 1st we need to understand a little about muscles and muscle physiology.
Muscles are composed of small individual units called sarcomeres. Inside of these “sarcomeres” there are interdigitating fibers of actin and myosin (proteins) which interact with one another like a ratchet when a muscle contracts. Sarcomeres can be of various lengths, depending on the muscle, and are linked and together from one end of the muscle to the other. When a muscle contracts concentrically (the muscle shortening while contracting) the ends of the sarcomere (called Z lines or Z discs) are drawn together, shortening the muscle fiber over all (see the picture above).
Signals are sent from the brain (actually the precentral gyrus of the cerebral cortex areas 4, 4s and 6) down the corticospinal tract to the spinal cord to synapse on motor neurons there. These motor neurons (alpha motor neurons) then travel through peripheral nerves to the muscles to cause them to contract (see picture above).
The resting length of the muscle is dependent upon two factors: The physical length of the muscle 2. The “tone” of the muscle in question.
The physical length of the muscle is determined by the length of the sarcomeres and the number of them in the muscle. The “tone” of the muscle determined by an interplay of neurological factors and the feedback loops between the sensory (afferent) receptors in the muscle (Ia afferents, muscle spindles, Golgi tendon organs etc.), relays in the cerebellum and basal ganglia as well as input from the cerebral cortex.
If you’re trying to “physically lengthen” a muscle, then you will need to actually add sarcomeres to the muscle. Research shows that in order to do this with static stretching it must be done 20 to 30 minutes per day per muscle.
If you were trying to “bring a muscle to its physiological limit” there are many stretching methods to accomplish this. Pick your favorite whether it be a static stretch, contract/ relax, post isometric relaxation etc. and you’ll probably be able to find a paper to support your position.
Remember with both not to ignore neurological reflexes (see above). Muscle spindle loops are designed to provide feedback to the central nervous system about muscle length and tension. Generally speaking, slow stretch activates the Ia afferent loop which causes causes physiological contraction of the muscle (this is one of the reasons you do not want to do slow, steady stretch on a muscle in spasm). This “contraction” can be fatigued overtime, causing the muscle to be lengthened to it’s physiological limit. Do this for an extended period of time (20-30 mins per day) and you will physically add sarcomeres to the muscle.
Next time you are stretching, or you were having a client/patient stretch, think about what it is that you’re actually trying to accomplish because there is a difference.
We are and remain The Gait Guys. Bald, good-looking, and above-average intelligence. Spreading gait literacy with each post we publish.
thanks to scienceblogs.com for the corticospinal tract image
-“Four weeks of hip external rotator and abductor strengthening significantly improves postural control in patients with functional ankle instability (FAI) and may be useful for preventing recurrent instability, according to research from Indiana University in Bloomington.”
Nothing new here, at least not here on The Gait Guys blog. We have been talking about these kinds of issues for a long time. We have long discussed the necessary control of the glutes (and their anchoring abdominals) to eccentrically control the loading response during the stance phase of gait, we especially like to discuss the control of the rate of internal rotation (read: eccentric ability of external rotators as a component) of the leg with the glutes. It is why we think it is so important to eccentrically test the glutes and the core stabilizers (all of them !) when the client is table assessed because it is a huge window for us as to what is happening when there is ground interface. Sure one is open chain and the other is closed, but function is necessary in both.
What this article is again, like others, telling us is that the ability to stack the joints (knee over foot, hip over knee, level stable pelvis over hip) improves postural control, especially when there is a risky environment of ankle functional or anatomical instability.
And yes, we are talking Cross over gait and frontal plane challenges and faulty patterns here. Failure to stack the joints usually leads to cross over gait challenges (type in “cross over or cross over gait into our blog SEARCH box). Remember though, you must selectively strengthen the weak muscles and weak motor patterns, if you are not specific you can easily strengthen the neuro-protective tight muscles and their patterns because they have been the only available patterns to your client. If you are not careful, you will help them strategize and compensate deeper, which in itself can lead to injury. This is a paramount rehab principle, merely activating what appears weak does not mean you are carrying them over to a functional pattern. Just because you can show a change on the table doesn’t mean it carries over to the ground and sport or training.
We are sure you have read many articles, some written by us, about the good the bad and the ugly about stretching.Regardless of how you slice the cake, we think we can all agree that stretching “feels” good. The question of course is “Why?”
Like it or not, it all boils down to neurology. Our good old friends, the Ia afferents are at least partially responsible, along with the tactile receptors, like Pacinian corpuscles, Merkel’s discs, Golgi tendon organs, probably all the joint mechanoreceptors and well as a few free nerve endings. We have some reviews we have written of these found here, and here and here.
What do all of these have in common? Besides being peripheral receptors. They all pass through the thalamus at some point (all sensation EXCEPT smell, pass through the thalamus) and the information all ends up somewhere in the cortex (parietal lobe to tell you where you are stretching, frontal lobe to help you to move things, insular lobe to tell you if it feels good, maybe the temporal lobe so you remember it, and hear all those great pops and noises and possibly the occipital lobe, so you can see what you are stretching.
The basic (VERY basic) pathways are:Peripheral receptor-peripheral nerve-spinal cord-brainstem-thalamus-cortex; we will call this the “conscious” pathway: and peripheral receptor-peripheral nerve-spinal cord-brainstem-cerebellum- cortex; we will call this the “unconscious” pathway.
Of course, the two BASIC pathways cross paths and communicate with one another, so not only can you “feel” the stretch with the conscious pathway but also know “how much” you are stretching through the unconscious pathway. The emotional component is related through the insular lobe (with relays from the conscious and unconscious pathways along with collaterals from the temporal lobe to compare it with past stretching experiences) to the cingulate gyrus and limbic cortex,where stretching is “truly appreciated”.
As we can see, there is an interplay between the different pathways and having “all systems go” for us to truly appreciate stretching from all perspectives; dysfunction in one system (due to a problem, compensation, injury, etc) can ruin the “stretching experience”.
Hopefully we have stretched your appreciation (and knowledge base) to understand more about the kinesthetic aspect of stretching. We are not telling you to stretch, or not to stretch, merely offering a reason as to why we seem to like it.