Author(s): NAKATANI, T., OHARA, S., NADAMOTO, M., Institution: TENRI UNIVERSITY, Country: JAPAN, Abstract-ID: 191

INTRODUCTION:
Age-related declines in muscle strength and function impair activities of daily living [1]. Shoulder muscles are essential for activities of daily living, enabling arm movements in multiple planes. Shoulder strength is critical for tasks such as carrying, lifting, hanging laundry, reaching overhead, and dressing [2]. This study investigated age- and sex-related differences in shoulder horizontal adduction strength (SHAS) among healthy Japanese adults aged 50–93 years.
METHODS:
Participants were 1098 healthy adults aged 50–93 years (451 men and 647 women). Exclusion criteria included certification for long-term care and orthopedic conditions that could affect muscle strength measurements. SHAS was measured in a standing position, with the participants holding a dynamometer in front of their chest and exerting maximum isometric force for 3–5 s. Age and horizontal adduction strength served as independent and dependent variables, respectively, for the simple linear regression analysis. Sex differences in the regression slopes were assessed using ANCOVA with a test for parallelism. For age group comparisons, the participants were divided into four age groups (50–59, 60–69, 70–79, and ≥80 years) by sex, with multiple comparisons conducted using Bonferroni correction against the 50–59-year age group as the reference. Statistical significance was set at p < 0.05.
RESULTS:
Simple linear regression analysis revealed a significant age-related decline in SHAS for both sexes (men: r = −0.395, p < 0.001; women: r = −0.399, p < 0.001). Two-way ANCOVA demonstrated a significant sex-by-age interaction (F(1, 1094) = 12.3, p < 0.001), with decline rates of 13.1% per decade in men and 12.5% per decade in women. Compared to the 50–59-year reference group, both sexes exhibited significantly lower strength in the 70–79 years and ≥80 years age groups (p < 0.001). Men demonstrated significantly higher strength than women across all age groups (p < 0.001).
CONCLUSION:
This study demonstrated that SHAS decreases with aging in Japanese middle-aged and older adults, with decline rates of 13.1% per decade in men and 12.5% per decade in women. Men maintained significantly higher strength than women across all age groups, and both sexes exhibited significantly lower strength beginning in the 70–79-year age group. The significant decline in SHAS beginning in the 70s (70–79 and ≥80 years age groups) suggests that preventive interventions should be initiated before this critical age.
References:
[1] Riviati N. and Indra B., Sage Open Med 11, 1-13 (2023)
[2] McGee C. W. et al., OTJR 23(4), 143-154 (2003)
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