Sarcopenia: Aging-Related Loss of Muscle Mass and Function
Larsson L, Degens H, Li M, Salviati L, Lee Y, Thompson W, Kirkland JL, Sandri M · Physiological Reviews · 2019 January 01
DOI 10.1152/physrev.00061.2017
Objective
To investigate the aging-related structural changes and cellular and subcellular mechanisms underlying alterations in individual motor units, including alpha motoneurons, neuromuscular junctions, and innervated muscle fibers, in sarcopenia.
Conclusions
Sarcopenia is driven largely by progressive motoneuron loss, inadequate reinnervation, reduced muscle fiber number and size, and disrupted muscle protein regulation, while experimental interventions may help preserve motor unit structure and function and potentially improve mobility.
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Insights
Age-related muscle loss chiefly reflects motor neuron loss and incomplete reconnection of muscle fibers, disrupting the coordinated systems required for muscle function.
This review synthesised evidence on age-related structural and cellular changes across the motor unit, examining motor neuron cell bodies, nerve-to-muscle connections, and the muscle fibers they control. It also considered intracellular alterations in muscle proteins, energy-producing structures, and calcium-regulating systems, alongside findings from experimental models of impaired nerve supply.
The review found that progressive motor neuron loss reduces both the number and size of muscle fibers, while surviving motor neurons cannot sufficiently restore lost connections. Declining muscle performance is further driven by altered protein modification and disrupted coordination among contractile, energy-producing, and calcium-handling proteins, linking normal aging changes to neuromuscular disease processes.
