The aim of this study was to investigate the association between the rate of torque development and maximal motor unit discharge frequency in young and elderly adults as they performed rapid submaximal contractions with the ankle dorsiflexors. Recordings were obtained of the torque exerted by the dorsiflexors during the isometric contractions and the surface and intramuscular electromyograms (EMGs) from the tibialis anterior. The maximal rate of torque development and integrated EMG (percentage of total EMG burst) at peak rate of torque development during fast contractions were lower in elderly than young adults by 48% (P < 0.05) and 16.5% (P < 0.05), respectively. The young adults, but not the elderly adults, exhibited a positive association (r2 = 0.33; P < 0.01) between the integrated EMG computed up to the peak rate of torque development and the maximal rate of torque development achieved during the fast contractions. These age-related changes during fast voluntary contractions were accompanied by a decline (P < 0.001) in motor unit discharge frequency (19, 28, and 34% for first 3 interspike intervals, respectively) and in the percentage of units (45%; P < 0.05) that exhibited double discharges (doublets) at brief intervals (<5 ms). Because aging decreased the maximal rate of torque development of fast voluntary contractions to a greater extent ( approximately 10%) than that of an electrically evoked twitch, collectively the results indicate that the age-related decline in maximal motor unit discharge frequency likely limit, in addition to the slowing of muscle contractile properties, the performance of fast voluntary contractions.

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No abstract

Classical studies in animal preparations suggest a strong role for spinal control of posture. In humans it is now established that the cerebral cortex contributes to postural control of unperturbed and perturbed standing. The age-related degeneration and accompanying functional changes in the brain, reported so far mainly in conjunction with simple manual motor tasks, may also affect the mechanisms that control complex motor tasks involving posture. This review outlines the age-related structural and functional changes at spinal and cortical levels and provides a mechanistic analysis of how such changes may be linked to the behaviorally manifest postural deficits in old adults. The emerging picture is that the age-related reorganization in motor control during voluntary tasks, characterized by differential modulation of spinal reflexes, greater cortical activation and cortical disinhibition, is also present during postural tasks. We discuss the possibility that this reorganization underlies the increased coactivation and dual task interference reported in elderly. Finally, we propose a model for future studies to unravel the structure-function-behavior relations in postural control and aging.

Purpose Measurement of muscle mass is paramount in the screening and diagnosis of sarcopenia. Besides muscle quantity however, also quality assessment is important. Ultrasonography (US) has the advantage over dual-energy X-ray absorptiometry (DEXA) and bio-impedance analysis (BIA) to give both quantitative and qualitative information on muscle. However, before its use in clinical practice, several methodological aspects still need to be addressed. Both standardization in measurement techniques and the availability of reference values are currently lacking. This review aims to provide an evidence-based standardization of assessing appendicular muscle with the use of US. Methods A systematic review was performed for ultrasonography to assess muscle in older people. Pubmed, SCOPUS and Web of Sciences were searched. All articles regarding the use of US in assessing appendicular muscle were used. Description of US-specific parameters and localization of the measurement were retrieved. Results Through this process, five items of muscle assessment were identified in the evaluated articles: thickness, crosssectional area, echogenicity, fascicle length and pennation angle. Different techniques for measurement and location of measurement used were noted, as also the different muscles in which this was evaluated. Then, a translation for a clinical setting in a standardized way was proposed. Conclusions The results of this review provide thus an evidence base for an ultrasound protocol in the assessment of skeletal muscle. This standardization of measurements is the first step in creating conditions to further test the applicability of US for use on a large scale as a routine assessment and follow-up tool for appendicular muscle.