To
prevent pain, need balanced pull of muscles, as joints rotate.
Without
balance, joint axes ("instant center of motion") will move incorrectly
causing stress and wear on joints, producing misalignment and pain.
1.
Force couples: Muscles pull in different directions, must be
balanced to rotate joints around an axis correctly or will cause pain.
E.g. upper and lower trap during upward rotation. If lower trap is weak, scapula will stay
downwardly tipped, produce impingement at the shoulder.
E.g. TFL with glut maximus during hip abduction (also
anterior and posterior gluteus medius).
Weight bearing, would cause hip
rotation if unbalanced, cause knee and ankle misalignment.
E.g. During elevation of the arm, if posterior shld cuff
muscles are too weak, will get anterior subluxation of The humeral head by the
deltoid and pect major.
2.
Muscle length: Muscles that are too long or too short will
cause abnormal motion, pain.
Muscles habitually kept in a stretched position grow more
sarcomeres, cannot strongly contract in shortened range, sometimes called stretch weakness. The muscles become longer.
Muscles habitually kept in a shortened position lose
sarcomeres cannot be lengthened
normally. The muscles become shorter.
Too short: E.g. Short pects and intercostals prevent
thoracic extension, shoulder retraction
E.g. Short hip flexors cause anterior tilt of pelvis when in
standing
Unilateral short hip flexors cause the
pelvis to rotate forward at the end of stance each step, rotating the lumbar
spine
E.g. Short lumbar extensors cause excessive lumbar extension
(lordosis)
Too long: E.g. Long thoracic extensors causes
kyphosis
E.g. Long abdominals causes lumbar lordosis
E.g. Long hip abductors on one side, long adductors on the
other side cause the pelvis to be positioned to the side of the long abductors,
causes lumbar
scoliosis
E.g. Long upper trapezeii cause shoulders to be too low,
produce TOS (thoracic outlet syndrome)
E.g. If the pect minor is
too tight, lower trapezius too long, the scapula will stay
downwardly tipped, causing impingement at the shoulder during
reaching.
General
rule: Need to lengthen shortened muscles
first to permit normal excursion. If
strengthen first, may compound the problem.
(can do simultaneously)
E.g. if have tight pects and subscapularis, strengthening
middle trap, infraspinatus and teres minor may just produce less shoulder
motion overall.
General
rule: To shorten a posturally lengthened
muscle, exercise it in its SHORTENED RANGE, against MINIMAL RESISTANCE.
E.g. if have forward, downwardly tipped scapulae, strengthen
stretched lower trapezius by doing depression with the shoulder in full flexion
against a wall or prone.
3. Muscle recruitment - The CNS can incorrectly learn to use one muscle rather than
another, causing weakness in the underused muscle, tightness in the over used
muscle.
E.g. If use
hamstrings for hip extension, not gluteus maximus, get weakness of glut, tightness
of hamstrings
E.g.
If use lateral hamstrings, not medial ones for knee flexion, get
laterally rotated knee
E.g. If use lumbar
extensors instead of hip extensors at end of stance to push off, get lumbar
pain
E.g. If don't push off well with gastrocs, get
pain in ant tibialis from constant contraction,
ischemia (shin splints)
4. Relative
flexibility - "Stretchability" or flexibility is associated with
muscle 1) tightness 2) looseness and with CNS recruitment.
Either excess alters motion, causing
pain-producing movements. This pain is
generally in the segment that gets too much motion.
General rule: proximal muscles should stabilize
segments so most of the motion occurs at the distal joint (or get pain
syndrome).
E.g. Hip should bend, not lumbar spine during
bending/lifting.
E.g. If abdominals are more flexible than rectus femoris, as
knee is flexed, rectus will pull pelvis into anterior tilt, cause lumbar pain.
E.g. If bending "at the waist" occurs at the
lumbar spine instead of at the hip, get lumbar pain. (common in tight hamstrings).
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