Post by eliuri on Feb 22, 2015 3:50:44 GMT -5
Muscle co-contraction is when opposing muscles are contracted simultaneously, such as when one tries to immobilize a joint.
You can try to see what that might feel like if that's held strongly or for long stretches of time. For example try clenching your jaw while your mouth is open so that its rigidly fixed. More relevant: Try rigidly clenching or immobilizing your neck in place by tensing up the muscles in back of your neck so that your head cannot move. Oddly, I find in both attempts there's an increased vibrational motion at those joints, almost like a buzzing or slight induced tremor. Eventually, pain will ensue..
Some degree of co-contraction is needed to maintain an upright posture. However, those who have developed a fearful stance, consciously or unconsciously, may be doing this type of "clenching" to excess.
Current theory of Phobic Postural Vertigo, the forerunner of CSD, is that subjective sensations of disequilibrium are often associated with increased frequency in the postural sway. The sway path is actually diminished, so that there is less displacement of the body's CoP (center of pressure), but the sway frequency is significantly increased in such cautious gait. This is actually an adaptive way to walk in some precarious conditions--if you're walking on ice for example. You want to keep your body's center as close to the base of support as is possible. However, in everyday walking, it might be highly maladaptive and exhausting on account of the sheer wastage of muscular energy. A more expansive but lower frequency sway pattern is actually more stable. This increase sway frequency might be at the core of the sense of disequilibrium experienced in PPV/CSD.
While most of us are directly aware of the muscle tension, pain, stiffness and soreness in the neck/shoulder region. it might very well be that the main culprit, as far as muscle group is concerned, is far more pedestrian. It might well be the co-contraction of muscles in the legs which partially clench the ankle joint leading to increased sway frequency. The muscles which control flexion and extension of that joint are actually two muscles in the lower leg: the soleus and tibialis anterior. I'm sure it's far more complicated, and more muscles are brought into play, but those two had been mentioned in terms of co-contraction of the foot among subjects with fear of heights. (See journal article about this uploaded to this forum). In that study of those with fear of heights the two muscle groups with increased co-contraction were muscles of the neck (moderate co-contraction index) and those of the feet (high co-contraction index)
Here's how Thomas Brandt phrased this with regard to Phobic Postural Vertigo:
Obviously, muscle tension is far from the only process giving rise to the cascade of events here. There's the disruption of the normal interplay between open-loop and closed loop postural control as well. But perhaps tackling the muscular finding here might be a more practical way to begin resolving this. There's a vicious cycle of events here which seems quite hard to break, as put forth by that University of Munich group:
So the question remains: How can those co-contractions, especially those of the legs, but optimally those of the neck as well, be successfully diminished?
~Eli
You can try to see what that might feel like if that's held strongly or for long stretches of time. For example try clenching your jaw while your mouth is open so that its rigidly fixed. More relevant: Try rigidly clenching or immobilizing your neck in place by tensing up the muscles in back of your neck so that your head cannot move. Oddly, I find in both attempts there's an increased vibrational motion at those joints, almost like a buzzing or slight induced tremor. Eventually, pain will ensue..
Some degree of co-contraction is needed to maintain an upright posture. However, those who have developed a fearful stance, consciously or unconsciously, may be doing this type of "clenching" to excess.
Current theory of Phobic Postural Vertigo, the forerunner of CSD, is that subjective sensations of disequilibrium are often associated with increased frequency in the postural sway. The sway path is actually diminished, so that there is less displacement of the body's CoP (center of pressure), but the sway frequency is significantly increased in such cautious gait. This is actually an adaptive way to walk in some precarious conditions--if you're walking on ice for example. You want to keep your body's center as close to the base of support as is possible. However, in everyday walking, it might be highly maladaptive and exhausting on account of the sheer wastage of muscular energy. A more expansive but lower frequency sway pattern is actually more stable. This increase sway frequency might be at the core of the sense of disequilibrium experienced in PPV/CSD.
While most of us are directly aware of the muscle tension, pain, stiffness and soreness in the neck/shoulder region. it might very well be that the main culprit, as far as muscle group is concerned, is far more pedestrian. It might well be the co-contraction of muscles in the legs which partially clench the ankle joint leading to increased sway frequency. The muscles which control flexion and extension of that joint are actually two muscles in the lower leg: the soleus and tibialis anterior. I'm sure it's far more complicated, and more muscles are brought into play, but those two had been mentioned in terms of co-contraction of the foot among subjects with fear of heights. (See journal article about this uploaded to this forum). In that study of those with fear of heights the two muscle groups with increased co-contraction were muscles of the neck (moderate co-contraction index) and those of the feet (high co-contraction index)
Here's how Thomas Brandt phrased this with regard to Phobic Postural Vertigo:
They increase their postural sway during
normal stance by co-contracting the flexor and extensor
muscles of the foot, evidently an expression of an unnecessary,
fearful strategy for maintaining stance.
Healthy subjects use this strategy only when in real danger
of falling.
During difficult balancing tasks, such as
tandem stance with eyes closed, the posturographic data
of these patients do not differ from those of healthy subjects,
i. e., the more difficult the demands of balance, all
the more “healthy” is the balance performance of patients
with phobic postural vertigo [25].
Obviously the fearful strategy, stance with unnecessary co-contraction of muscles, is reversible, although this has not yet been experimentally proven in a follow-up study using quantitative
posturography.
Brandt: Phobic postural vertigo: A long-term follow-up (5 to 15 years) of 106 patients: J Neurol (2005) 252 : 564–569
normal stance by co-contracting the flexor and extensor
muscles of the foot, evidently an expression of an unnecessary,
fearful strategy for maintaining stance.
Healthy subjects use this strategy only when in real danger
of falling.
During difficult balancing tasks, such as
tandem stance with eyes closed, the posturographic data
of these patients do not differ from those of healthy subjects,
i. e., the more difficult the demands of balance, all
the more “healthy” is the balance performance of patients
with phobic postural vertigo [25].
Obviously the fearful strategy, stance with unnecessary co-contraction of muscles, is reversible, although this has not yet been experimentally proven in a follow-up study using quantitative
posturography.
Brandt: Phobic postural vertigo: A long-term follow-up (5 to 15 years) of 106 patients: J Neurol (2005) 252 : 564–569
Obviously, muscle tension is far from the only process giving rise to the cascade of events here. There's the disruption of the normal interplay between open-loop and closed loop postural control as well. But perhaps tackling the muscular finding here might be a more practical way to begin resolving this. There's a vicious cycle of events here which seems quite hard to break, as put forth by that University of Munich group:
Hypothesized circular cascade of symptom emergence in
PPV. Arrow lines indicate the direction of the causal chain. Dotted
arrow lines indicate that the causal connection has to be further
investigated.
(1) A conscious concentration on control of postural
stability might trigger
(2) co-contraction of anti-gravity muscles,
thereby causing
(3) an inadequate mode of interaction between open and
closed-loop mechanisms within the postural control systems. This
might lead to
(4) subjective imbalance, which in turn would enhance
(1) conscious control of posture
From: "Inadequate interaction between open- and closed-loop postural control in phobic postural vertigo": M. Wuehr T. Brandt • K. Jahn • R. Schniepp: J Neurol 2012
PPV. Arrow lines indicate the direction of the causal chain. Dotted
arrow lines indicate that the causal connection has to be further
investigated.
(1) A conscious concentration on control of postural
stability might trigger
(2) co-contraction of anti-gravity muscles,
thereby causing
(3) an inadequate mode of interaction between open and
closed-loop mechanisms within the postural control systems. This
might lead to
(4) subjective imbalance, which in turn would enhance
(1) conscious control of posture
From: "Inadequate interaction between open- and closed-loop postural control in phobic postural vertigo": M. Wuehr T. Brandt • K. Jahn • R. Schniepp: J Neurol 2012
So the question remains: How can those co-contractions, especially those of the legs, but optimally those of the neck as well, be successfully diminished?
~Eli