Impact of Aging on Musculotendinous Architecture of Supraspinatus in Healthy Individuals: A Comparative Analysis of Young Versus Elderly Populations

Background and Purpose: Muscle and tendon may exhibit degenerative changes with aging. For suprapinatus, alterations of musculotendinous architecture as fiber bundle length (FBL) and pennation angle (PA) are associated with the severity of tendinopathy. However, the changes in FBL and PA of supraspinatus in healthy elderly remains unknown. This study aims to compare the musculotendinous architecture of supraspinatus between healthy young and elderly individuals to explore the impact of aging. Methods: Fifteen healthy young (20.2 ± 0.9 years) and eighteen elderly (61.0 ± 7.2 years) participants with asymptomatic shoulder underwent ultrasound imaging to assess the supraspinatus musculotendinous architecture, FBL and PA, in resting, scaption at 30°, and stretching positions. Maximal strength and flexibility of supraspinatus were also measured. Independent t-test was used to compare differences in musculotendinous architecture, supraspinatus muscle strength, and horizontal abduction angle between the elderly and young participants. The Pearson correlation coefficient was used to analyze the correlation between the supraspinatus musculotendinous architecture and muscle strength. The statistical significance level was set at P < 0.05. Results: No significant difference in FBL at rest between the elderly and the young participants. However, young individuals showed significantly larger PA than the elderly (young: 15.3 ± 2.1°, elderly: 11.7 ± 1.1°, P < 0.001). The changes of FBL (young: 0.4 ± 0.2mm, elderly: 0.2 ± 0.1mm, P = 0.04) and PA (young: 2.0 ± 0.8°, elderly: 1.4 ± 0.7°, P = 0.039) from rest to stretch were significantly greater in young than the elderly. The horizontal shoulder abduction angle (young: 57.3 ± 7.9°, elderly: 38.3 ± 9.3°, P < 0.001) and supraspinatus strength (young: 9.8 ± 1.8 kg, elderly: 5.9 ± 2.8 kg, P < 0.001) in young individuals were significantly greater than the elderly. A significant correlation was found between PA and muscle strength in different postures (resting: r = 0.536, P < 0.001; scaption at 30°: r = 0.465, P = 0.006; stretching: r = 0.549, P < 0.001), but no significant correlation between FBL and strength. Conclusion: The changed musculotendinous architecture of supraspinatus was found in elderly changes with age and associated with the declined strength and flexibility. Clinical Relevance: For the aging and asymptomatic shoulder, conditioning exercise may be designed for improving the strength and flexibility of supraspinatus. Future research may address the relationship between the supraspinatus musculotendinous architecture and daily functions in elderly.