View Full Version : Re: summary of stiffness, reply to summary

Bryan Kirking
04-24-1998, 06:58 AM
HI Gregory, I don't remember seeing your original post, but I thought I might add something now, it may be that some of you other replies mentioned this and you already filtered it, but here it goes anyway.

If I understand you line of thinking, the abs and the hip flexors are working against each other by both pulling on the pelvis. Thus, altering pelvic position may be achievable by altering the total force on the pelvis which is a combination of the superiorly directed force (abs) or inferiorly directed force (hips).

If you assume the pelvis rotates around the hip joint, then Sum of moments about hip equals Ab force times Ab moment arm minus Hipflexor force times Hipflexor moment arm.

Now then, lets assume you don't want to surgically alter the muscle origins or insertions to change moment arms (this is done by the way in some gait correction procedures). This means you can alter pelvic position by changing only ab or hip force. Increasing ab strength could mean greater Action Potential signal, greater muscle area, or change in the length strength property of the muscle, as you suggest. Decreasing hip flexor strength could mean reduction of Action Potential signal, muscle area, ultimate muscle stress, or change in length strength property.

**** It seems to me that an increase in ab muscle rest length would be opposite what you want, since that would mean the muscle would need to be longer to supply the force needed to balance the hip flexors and the lengthening of the muscle would create ***** while increasing the Action potential, ultimate stress, or the muscle area of the abs would be more likely to produce the effect you desire.

An approach that worked to both increase abdominal size (muscle area) while similarly decreasing the passive portion of the hip flexor muslce/tendon complex (i.e. increasing flexibility) would seem to me to be the most likely to succeed in altering tilt the way I think you want it altered.

I didn't supply any sources which is what you are asking for, but if
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