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Differential age‐related changes in motor unit properties between elbow flexors and extensors
Author(s) -
Dalton B. H.,
Jakobi J. M.,
Allman B. L.,
Rice C. L.
Publication year - 2010
Publication title -
acta physiologica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.591
H-Index - 116
eISSN - 1748-1716
pISSN - 1748-1708
DOI - 10.1111/j.1748-1716.2010.02100.x
Subject(s) - isometric exercise , biceps , elbow flexion , motor unit , medicine , elbow , ageing , muscle contraction , anatomy , physical medicine and rehabilitation , contraction (grammar) , electromyography , weakness , motor unit recruitment , cardiology
Abstract Aim: Healthy adult ageing of the human neuromuscular system is comprised of changes that include atrophy, weakness and slowed movements with reduced spinal motor neurone output expressed by lower motor unit discharge rates (MUDRs). The latter observation has been obtained mostly from hand and lower limb muscles. The purpose was to determine the extent to which elbow flexor and extensor contractile properties, and MUDRs in six old (83 ± 4 years) and six young (24 ± 1 years) men were affected by age, and whether any adaptations were similar for both muscle groups. Methods: Maximal isometric voluntary contraction (MVC), voluntary activation, twitch contractile properties, force–frequency relationship and MUDRs from sub‐maximal to maximal intensities were assessed in the elbow flexors and extensors. Results: Both flexor and extensor MVCs were significantly ( P < 0.05) less (∼42% and ∼46% respectively) in the old than in the young. Contractile speeds and the force–frequency relationship did not show any age‐related differences ( P > 0.05). For the elbow flexors contraction duration was ∼139 ms and for the extensors it was ∼127 ms for both age groups ( P > 0.05). The mean MUDRs from 25% MVC to maximum were lower (∼10% to ∼36%) in the old than in the young ( P < 0.01). These age‐related differences were larger for biceps (Cohen’s d = 8.25) than triceps (Cohen’s d = 4.79) brachii. Conclusion: Thus, at least for proximal upper limb muscles, mean maximal MUDR reductions with healthy adult ageing are muscle specific and not strongly related to contractile speed.