Age-Related Changes in Morphology and Function of Scapular Muscles in Asymptomatic People.
BACKGROUND
Aging is a contributing factor to rotator cuff tears. Dysfunction of the scapular muscles can be a potential cause of rotator cuff tears. Although aging can contribute to dysfunction of the scapular muscles and subsequently result in rotator cuff tears, the effects of aging on scapular muscles are unclear.


OBJECTIVE
To determine changes in sizes and electromyographic activities of the scapular muscles with age in asymptomatic subjects.


METHODS
Cross-sectional study.


METHODS
Fifty-four asymptomatic subjects without shoulder pain and dysfunction (18 male and 36 female) were recruited for this study. Subjects consisted of 19 people aged 20-39 years (young adult group, 27.2 ± 5.2 years), 17 people aged 40-59 years (middle age group, 49.9 ± 6.6 years), and 18 people aged 60-79 years (elderly group, 68.0 ± 7.1 years).


METHODS
Using ultrasonography, we measured the muscle thickness of the trapezius (upper and lower portions), serratus anterior, and middle deltoid muscles during rest with the subject in a sitting position. Activities of the same muscles were measured with surface electromyography during shoulder elevation in the scapular plane up to 120°. The electromyographic data were analyzed at ranges 0°-30°, 30°-60°, and 60°-90°. Analysis of variance and Bonferroni multiple comparisons were used for statistical analysis.


RESULTS
Muscle thickness of the lower trapezius in the elderly group was decreased significantly compared with that in the young adult group (95% confidence interval -0.40, 2.24; P < .001) and middle age group (95% confidence interval -0.34, 1.89; P = .012). There were no significant differences in muscle activity and activity ratio between groups.


CONCLUSIONS
In scapular muscles, muscle thickness of the lower trapezius significantly decreased with aging, although there were no decreases in muscle thicknesses of the other muscles between different age groups. For the functional change, aging may not affect the scapular muscle activities and balance of the activities between the deltoid and scapular muscles.


METHODS
IV.
Department of Physical Medicine and Rehabilitation, Tohoku University Graduate School of Medicine, Sendai, Japan(∗).
Shuhei
S
Morise
Department of Physical Medicine and Rehabilitation, Tohoku University Graduate School of Medicine, 2-1 Seiryo-cho, Aoba-ku, Sendai 980-8575, Japan(†). Electronic address: takayukimurakipt@yahoo.co.jp.
Takayuki
T
Muraki
Department of Physical Medicine and Rehabilitation, Tohoku University Graduate School of Medicine, Sendai, Japan(‡).
Hiroaki
H
Ishikawa
Department of Physical Medicine and Rehabilitation, Tohoku University Graduate School of Medicine, Sendai, Japan(§).
Shin-Ichi
SI
Izumi
D000328:Adult; D000367:Age Factors; D000368:Aged; D000375:Aging / Q000502:physiology*; D003430:Cross-Sectional Studies; D004576:Electromyography / Q000379:methods*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects; D016059:Range of Motion, Articular / Q000502:physiology*; D012016:Reference Values; D018570:Risk Assessment; D012540:Scapula / Q000033:anatomy & histology / Q000000981:diagnostic imaging / Q000502:physiology; D012737:Sex Factors; D012782:Shoulder / Q000033:anatomy & histology / Q000502:physiology; D064171:Superficial Back Muscles / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000502:physiology*; D055815:Young Adult