Age-related changes in motor unit firing pattern of vastus lateralis muscle during low-moderate contraction

Abstract

Age-related changes in motor unit activation properties remain unclear for locomotor muscles such as quadriceps muscles, although these muscles are preferentially atrophied with aging and play important roles in daily living movements. The present study investigated and compared detailed motor unit firing characteristics for the vastus lateralis muscle during isometric contraction at low to moderate force levels in the elderly and young. Fourteen healthy elderly men and 15 healthy young men performed isometric ramp-up contraction to 70 % of the maximal voluntary contractions (MVC) during knee extension. Multichannel surface electromyograms were recorded from the vastus lateralis muscle using a two-dimensional grid of 64 electrodes and decomposed with the convolution kernel compensation technique to extract individual motor units. Motor unit firing rates in the young were significantly higher (~+29.7 %) than in the elderly (p < 0.05). There were significant differences in firing rates among motor units with different recruitment thresholds at each force level in the young (p < 0.05) but not in the elderly (p > 0.05). Firing rates at 60 % of the MVC force level for the motor units recruited at <20 % of MVC were significantly correlated with MVC force in the elderly (r = 0.885, p < 0.0001) but not in the young (r = 0.127, p > 0.05). These results suggest that the motor unit firing rate in the vastus lateralis muscle is affected by aging and muscle strength in the elderly and/or age-related strength loss is related to motor unit firing/ recruitment properties.

Age-specific differences in the time-frequency representation of surface electromyographic data recorded during a submaximal cyclic back extension exercise: a promising biomarker to detect early signs of sarcopenia

“…Muscle weakening and atrophy begin in the fourth decade of life with a rate of strength loss of approximately 1% per year, and accelerates in the later decades [3]. To date, a significant body of research has identified structural and morphological alterations in the muscles and the nervous system [4,5] that are all likely associated with the aging-related decline in neuromuscular functions, such as muscle weakness and reduced postural performance [6][7][8][9]. These age-dependent structural changes are known to be preceded by a loss of preferably highly myelinated axons that are the neuronal components of high threshold motor units (for review see [5,10]).…”

Central and Peripheral Neuromuscular Adaptations to Ageing

“…Through the use of an array of electrodes rather than the usual bipolar configuration, a more accurate decomposition of the EMG signal appears to be feasible and it has shown promising results with regards to neural drive and motor unit properties estimation. Only few studies that used high-density EMG have been performed on elderly adults [166,167]. They reported evidence of impaired motor unit discharge characteristics which indicates a reduced integrity of the motor unit firing modulation [165,166].…”

“…Only few studies that used high-density EMG have been performed on elderly adults [166,167]. They reported evidence of impaired motor unit discharge characteristics which indicates a reduced integrity of the motor unit firing modulation [165,166]. Developing this technique could be key to more extensively interpreting the neural and intrinsic changes occurring with ageing.…”

Food functionality research as a new national project in special reference to improvement of cognitive and locomotive abilities

“…It is thus necessary to identify some particularly desirable food components and develop them in AFF food items for application to QOL improvement ( Figure 3). A number of papers have already been published [50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69].…”