Age-related decline of motor unit firing rate in community-dwelling healthy older adults and daily ingestion of fish protein of Alaska pollack: a randomised trial

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Neuromuscular properties decline with ageing and low-level physical activities. Alaska pollack protein (APP) is reportedly effective for improving skeletal muscular functions, even if the amount is small and exercise is not conducted. However, it is unclear whether APP intake without an exercise program affects neuromuscular dysfunction in community-dwelling adults conducting normal, everyday activities. This study aimed to investigate changes in motor unit firing properties by adding APP to daily meals in community-dwelling older adults. They were divided into an APP group or a placebo control (CON) group for randomised, double-blind treatment. Participants in APP (n = 15) and CON (n = 17) groups ingested 4.5 g/d APP and whey protein, respectively, added to daily meals for 3 months without a specific exercise intervention. High-density surface electromyography of the vastus lateralis to assess the individual motor unit firing rate during 70% of maximum voluntary ramp-up contraction (MVC), maximum knee extensor strength, muscle thickness, echo intensity, and a physical function test were evaluated at the baseline, as well as 1.5 and 3 months after the intervention. While muscle strength, muscle thickness, and motor function were not changed, the motor unit firing rate at 50%–70% of MVC showed a significant decline at 1.5 and 3 months in the CON group, but this decline was not observed in the APP group. These findings suggest that neuromuscular properties show a detectable decline on performing daily activities without a specific exercise intervention, but such a decline was not observed in the APP intake group.