Abstract
We investigated the effect of resistance training and fish protein intake on the motor unit firing pattern and motor function in elderly. Fifty healthy elderly males and females (69.2 ± 4.7 years) underwent 6 weeks of intervention. We applied the leg-press exercise as resistance training and fish protein including Alaska pollack protein (APP) as nutritional supplementation. Subjects were divided into four groups: fish protein intake without resistance training (APP-CN, n = 13), placebo intake without resistance training (PLA-CN, n = 12), fish protein intake with resistance training (APP-RT, n = 12), and placebo intake with resistance training (PLA-RT, n = 13). Motor unit firing rates were calculated from multi-channel surface electromyography by the Convolution Kernel. For the chair-stand test, while significant increases were observed at 6 weeks compared with 0 week in all groups (p < 0.05), significant increases from 0 to 3 weeks and 6 weeks were observed in APP-RT (18.2 ± 1.9 at 0 week to 19.8 ± 2.2 at 3 weeks and 21.2 ± 1.9 at 6 weeks) (p < 0.05). Increase and/or decrease in the motor unit firing rate were mainly noted within motor units with a low-recruitment threshold in APP-RT and PLA-RT at 3 and 6 weeks (12.3 pps at 0 week to 13.6 pps at 3 weeks and 12.1 pps at 6 weeks for APP-RT and 12.9 pps at 0 week to 13.9 pps at 3 weeks and 14.1 pps at 6 weeks for PLA-RT at 50% of MVC) (p < 0.05), but not in APP-CN or PLA-CN (p > 0.05). Time courses of changes in the results of the chair-stand test and motor unit firing rate were different between APP-RT and PLA-RT. These findings suggest that, in the elderly, the effect of resistance training on the motor unit firing rate is observed in motor units with a low-recruitment threshold, and additional fish protein intake modifies these adaptations in motor unit firing patterns and the motor function following resistance training.
Highlights
The effect of exercise and nutrition interventions on muscle mass and function in the elderly have been investigated in numerous studies, and they have been accepted as essential to prevent age-related muscle atrophy and dysfunction (Dickinson et al, 2013)
Protein normalized by body weight significantly increased from PRE to 3–6 weeks for APPCN (p = 0.004), placebo intake without resistance training (PLA-CN) (p = 0.021), and placebo intake with resistance training (PLA-RT) (p = 0.023), but not for Alaska pollack protein (APP)-RT (p = 0.062) (Table 2)
No significant effects of intervention were noted on the body mass, body fat and muscle mass estimated by InBody, muscle and subcutaneous tissue thicknesses, maximal voluntary contraction (MVC), or gait time in any of the groups (p < 0.05) (Table 3)
Summary
The effect of exercise and nutrition interventions on muscle mass and function in the elderly have been investigated in numerous studies, and they have been accepted as essential to prevent age-related muscle atrophy and dysfunction (Dickinson et al, 2013). Our previous study identified a positive correlation between motor unit firing pattern of the vastus lateralis (VL) muscle and MVC force of the quadriceps femoris muscles in the elderly (Watanabe et al, 2016). This suggests that, in addition to the muscle volume or peripheral muscle morphology, the central nervous system plays an important role in physiological mechanisms leading to the age-related decline in muscle strength and its countermeasures. Quantification of the detailed functioning of the central nervous system is more difficult than that of the muscle mass due to methodological limitation
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