Hi Phil (and others of interest),
To quickly answer your question, all of the above (the ankle) influence/compensate COM velocity. Unfortunately at this time, I do not have references, but try it on yourself. Walk normally, then walk again and bend (flex) at the hip, keep this flexion and walk. Also try a side bend.
This alone becomes important when assessing patients, where the biomechanical functional exam needs to include (assessing) knee, hip and spine (trunk) orientation with respect to the frontal and sagittal planes, and ROM.
Re-training the muscles can be important, but re-training is best when done in the desired orientation. This is one very important reason why foot orthotics are such important, and in the help to re-align posture and joint axes (subtalar, ankle, knee and hip), and not just at the level of the foot.
For the mathematical folks, ROM and joint axes orientation affect joint moments, and hence power. Improving gait by reducing energy costs (power is a measure of energy) is a common theme, approach and desired outcome when assessing/treating amputee gait. The same applies to non-amputees who have altered (reduced) ROM and deviated axes in foot, at subtalar, ankle, knee and hip (one, some, or all).
To calculate moments, power and energy, ground reaction forces need to be measured (F vs. T curve). COM can also be calculated from the F vs. T curve (but does require total ground re-action force -sum of forces acting on both feet). This is already documented and reported in the literature and engineering textbooks on COM calculations/mathematics of bodies. The vertical component is the most important and influential. Much information is available when evaluating/observing the pattern of the F vs. T curve, and not just the amplitudes; left side vs. right side (symmetry), and with respect to the normal pattern (difference with normal curve). The normal pattern of the F vs. T curve (with respect to 100% body weight) is well documented in the literature. Research articles and books on gait analysis have been reporting this for over 1-2 decades.
Of interest to some, the hip is one major joint which influences gait (and posture), especially the SI joint. Assess (non-weight bearing on table or chair bed) for altered ROM at hip, and if ROM differs left-right, there is most often associated a weaker (muscle) side and SI blockage. Stretching, strengthening, and/or re-training the hip associated muscles, and having the SI joint(s) manipulated (un-blocked) does wonder to gait, especially at level of knee, hip and truck. In some cases, it can even reduce rearfoot excessive ROM. If the hip does not follow thru with full range of motion, somewhere needs to compensate. An ideal place to do so is at the subtalar. Hence, the subtalar joint axis deviates from the norm.
Re-align joint axes and/or release/compensate for blocked/rigid joints, and you will see/observe changes in pressure profiles, F vs. T curve patterns, CoF and COM trajectory, velocity and joint ROM (one, some and/or all). Their relationships and patterns, however, have yet to be determined. Muscle imbalance and blocked/rigid joints cause joint axes to deviate.
Bart (and colleagues) is on a very good and excellent path via his studies to provide us more information in the future. And yes, more than one parameter is required to explain (what I and colleagues try to do via lectures and workshops) and understand (hoping that those who attend such seminars do and come out with) foot function and gait. Pressure profiles, F vs. T curve patterns, CoF and COM trajectory, velocity and joint ROM (lack of) are excellent starters. Clinically, for some, this is a mode (approach) of practice (some use one parameter, others use more). Please remember, parameters do not prescribe, they help see and understand what is/not happening, thus much helping in deciding/writing the prescription.
Norman
-----Original Message-----
From: A group for the academic discussion of current issues in podiatry
[mailto:[log in to unmask]]On Behalf Of Philip Wells
Sent: Thursday, March 25, 2004 8:19 AM
To: [log in to unmask]
Subject: Extrinsic causes of COM deceleration
Dear all
I've just been reading some of the postings from a couple of months ago
re. the ability (or not) of the ankle plantar flexors in reducing the
velocity of the COM. (Makes sense.)
However the question I have is
'is this the prime mechaninism available to the body to acheive this or if
an absence is seen in the normal mechanism, can hip, spine and truck
musculuture compensate in any way?'
Looking at muscle balance around the pelvis, it seems that a possible
alternative approach may be re-training of these muscles.
Any comments would be helpfull? (I beleive this would be a valuable
approach in the diabetic patient as an adjunct to our normal treatments.
Phil
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