Middle-aged adults cocontract with arm ADductors during arm ABduction, while young adults do not. Adaptations to preserve pain-free function?
Middle-aged individuals cocontract with adductor muscles during abduction. This may be crucial for counteracting deltoid forces, depressing the humerus and ensuring free passage of subacromial tissues underneath the acromion during abduction. We questioned whether adductor co-contraction is always present, or develops during ageing, in which case it may explain the age-related character of common shoulder conditions such as Subacromial Pain Syndrome. In a cross-sectional analysis with electromyography (EMG), activation patterns of the latissimus dorsi, teres major, pectoralis major and deltoid muscle were assessed during isometric force tasks in 60 asymptomatic individuals between 21 and 60 years old. Cocontraction was expressed as the degree of antagonistic activation relative to the same muscle's degree of agonistic activation, resulting in an activation ratio between -1 and 1, where lower values indicate more cocontraction. Using linear regression analyses, we found age-related decreases in the activation ratio of the latissimus dorsi (regression estimate: -0.004, 95% CI: -0.007 to 0.0, p-value: 0.042) and teres major (regression estimate: -0.013, 95% CI: -0.019 to -0.008, p-value: <0.001). In contrast to young individuals, middle-aged individuals showed a high degree of adductor cocontraction during abduction. This may indicate that during ageing, alterations in activation patterns are required for preserving pain-free shoulder function.
['Overbeek|Celeste L|CL|', 'Kolk|Arjen|A|', 'de Groot|Jurriaan H|JH|', 'de Witte|Pieter Bas|PB|', 'Gademan|Maaike G J|MGJ|', 'Nelissen|Rob G H H|RGHH|', 'Nagels|Jochem|J|']
D000222:Adaptation, Physiological D000328:Adult D000375:Aging D057645:Deltoid Muscle D005260:Female D006801:Humans D008297:Male D008875:Middle Aged D009068:Movement D009119:Muscle Contraction D016059:Range of Motion, Articular D012785:Shoulder Joint D020069:Shoulder Pain D034941:Upper Extremity
Aging Electromyography Adductor cocontraction Humeral depression Joint stabilisation Shoulder Impingement Syndrome Shoulder stability Subacromial narrowing