The following few articles give us some interesting information on common
beliefs that exist about strengthening certain muscles in order to improve
stability of certain joints and enhance performance. The first one makes the
revolutionary conclusion that trunk and pelvic posture do not have any
significant effect on abdominal strength.
The second reference concludes controversially that shoulder retraction
exercises do not have a significant effect on shoulder posture.
Clearly, there is a great deal that needs to be re-examined in what is being
said about abdominal, shoulder and trunk stabilisation.
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1. Walker ML, Rothstein JM, Finucane SD, Lamb RL Relationships between
lumbar lordosis, pelvic tilt, and abdominal muscle performance. Phys Ther
1987 Apr;67(4):512-6
The results indicate that lumbar lordosis, pelvic tilt, and abdominal muscle
function during normal standing are not related. This study demonstrates the
need for a re-examination of clinical practices based on assumed relationships
of abdominal muscle performance, pelvic tilt, and lordosis.
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2. DiVeta J, Walker ML, Skibinski B Relationship between performance of
selected scapular muscles and scapular abduction in standing subjects. Phys
Ther 1990 Aug;70(8):470-6
Results indicate that no relationship exists between the position of the
scapula in standing subjects and the muscular force produced by the middle
trapezius and pectoralis minor muscles. Clinical practices based on an assumed
relationship between these variables (eg, the practice of using middle
trapezius muscle strengthening exercises to correct a forward shoulder
position) should be reexamined in light of these findings.
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An article showing that not only 'rotator cuff' issues are important in
shoulder rehabilitation:
3. Palmerud G, Sporrong H, Herberts P, Kadefors R Consequences of trapezius
relaxation on the distribution of shoulder muscle forces: an electromyographic
study. J Electromyogr Kinesiol 1998 Jun;8(3):185-93
This study was focused on the ability to reduce voluntarily the muscle
activity in the descending part of the trapezius muscle without changing the
arm position or hand load, and its consequences on the distribution of
shoulder muscle forces.
The anterior part of the deltoid and the medial part of the serratus anterior
also intensified their activity. The influence on the levator scapulae was,
contrary to simulation results and to empirical knowledge, a decrease of the
muscle activity. It is suggested that attention is given to the rhomboids and
the transverse part of the trapezius when muscle activity is reduced in the
descending part of the trapezius, for instance in biofeedback-based therapy.
In conclusion, the study showed that reducing the trapezius activity caused a
redistribution of muscle forces in the shoulder.
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More on the role of muscles other than the rotator cuff in shoulder integrity:
4. Arwert HJ, de Groot J, Van Woensel WW, Rozing PM Electromyography of
shoulder muscles in relation to force direction. J Shoulder Elbow Surg 1997
Jul-Aug;6(4):360-70
In a static force task the electromyographic level of 14 shoulder muscles
including 3 rotator cuff muscles was related to force direction. The principal
force direction of maximal electromyography was identified for every muscle.
The deltoid was active in a force direction that could be understood from its
anatomy. The trapezius and serratus were mainly involved in stabilizing the
scapula in upward and outward force directions. Large multiarticular muscles
such as the pectoralis and the latissimus were active in downward and forward
forces. The rotator cuff seems to have a specific role in stabilizing the
glenohumeral joint.
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Here is a reference that shows that paralysis of one of the rotator cuff
muscles does not prevent full glenohumeral abduction, suggesting that weakness
or even paralysis of certain rotator cuff muscles may not have the dire
consequences usually aimed at some rotator cuff weakness.
5. McMahon PJ, Debski RE, Thompson WO, Warner JJ, Fu FH, Woo SL Shoulder
muscle forces and tendon excursions during glenohumeral abduction in the
scapular plane. J Shoulder Elbow Surg 1995 May-Jun;4(3):199-208
A larger contribution of force from the supraspinatus was required near the
beginning of motion, whereas the middle deltoid was more important near the
end of glenohumeral abduction in the scapular plane. Tendon excursion for the
middle
deltoid and supraspinatus were proportionately larger than those for the
subscapularis and infraspinatus. Simulated supraspinatus paralysis does not
change normal joint kinematics and does not prevent full glenohumeral
abduction.
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Dr Mel C Siff
Denver, USA
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