Abstract
Aging processes in the musculoskeletal system lead to functional impairments that restrict participation. Purpose: To assess differences in the force and motor recruitment patterns of shoulder muscles between age groups to understand functional disorders. A cross-sectional study comparing 30 adults (20–64) and 30 older adults (>65). Surface electromyography (sEMG) of the middle deltoid, upper and lower trapezius, infraspinatus, and serratus anterior muscles was recorded. Maximum isometric voluntary contraction (MIVC) was determined at 45° glenohumeral abduction. For the sEMG signal registration, concentric and eccentric contraction with and without 1 kg and isometric contraction were requested. Participants abducted the arm from 0° up to an abduction angle of 135° for concentric and eccentric contraction, and from 0° to 45°, and remained there at 80% of the MIVC level while isometrically pushing against a handheld dynamometer. Differences in sEMG amplitudes (root mean square, RMS) of all contractions, but also onset latencies during concentric contraction of each muscle between age groups, were analyzed. Statistical differences in strength (Adults > Older adults; 0.05) existed between groups. No significant differences in RMS values of dynamic contractions were detected, except for the serratus anterior, but there were for isometric contractions of all muscles analyzed (Adults > Older adults; 0.05). The recruitment order varied between age groups, showing a general tendency towards delayed onset times in older adults, except for the upper trapezius muscle. Age differences in muscle recruitment patterns were found, which underscores the importance of developing musculoskeletal data to prevent and guide geriatric shoulder pathologies.
Highlights
Aging leads to a regression of physical capacities and a decrease in functionality in older people [1,2]
Significant differences observed between age groups in functionality and body mass index (p < 0.01, Adults < Older adults) as well as in Maximum isometric voluntary contraction (MIVC)
Significant differences were observed between age groups in functionality and body mass index (p < 0.01, Adults < Older adults) as well as in MIVC (p < 0.01, Adults > Older adults), active range of motion (ROM) p < 0.05, Adults > Older adults), and previous physi
Summary
Aging leads to a regression of physical capacities and a decrease in functionality in older people [1,2]. The proportion of older people will increase in the coming decades [5], so establishing normative data in order to improve diagnosis, prevention, and treatment is a necessity to reduce costs due to absence of information. In mid-adulthood, age-related changes appear that progressively decrease muscle function [1,6]. These natural aging changes are clinically defined as geriatric sarcopenia [7,8]. The muscle mass in skeletal muscle decreases, especially for type II fibers, which lead to a decrease in strength, with a consequent increase in muscle weakness [9]
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