What is the cause of the ageing atrophy? Total number, size and proportion of different fiber types studied in whole vastus lateralis muscle from 15- to 83-year-old men

https://www.thelancet.com/pdfs/journals/lancet/PIIS0140-6736(06)68175-0.pdf

Guillain-Barré syndrome

Aging is associated with progressive loss of neuromuscular function that often leads to progressive disability and loss of independence. The term sarcopenia is now commonly used to describe the loss of skeletal muscle mass and strength that occurs in concert with biological aging. By the seventh and eighth decade of life, maximal voluntary contractile strength is decreased, on average, by 20-40% for both men and women in proximal and distal muscles. Although age-associated decreases in strength per unit muscle mass, or muscle quality, may play a role, the majority of strength loss can be accounted for by decreased muscle mass. Multiple factors lead to the development of sarcopenia and the associated impact on function. Loss of skeletal muscle fibers secondary to decreased numbers of motoneurons appears to be a major contributing influence, but other factors, including decreased physical activity, altered hormonal status, decreased total caloric and protein intake, inflammatory mediators, and factors leading to altered protein synthesis, must also be considered. The prevalence of sarcopenia, which may be as high as 30% for those ≥60 yr, will increase as the percentage of the very old continues to grow in our populations. The link between sarcopenia and disability among elderly men and women highlights the need for continued research into the development of the most effective interventions to prevent or at least partially reverse sarcopenia, including the role of resistance exercise and other novel pharmacological and nutritional interventions.

Invited review: Aging and sarcopenia.

This brief review examines some of the methods used to infer central control strategies from surface electromyogram (EMG) recordings. Among the many uses of the surface EMG in studying the neural control of movement, the review critically evaluates only some of the applications. The focus is on the relations between global features of the surface EMG and the underlying physiological processes. Because direct measurements of motor unit activation are not available and many factors can influence the signal, these relations are frequently misinterpreted. These errors are compounded by the counterintuitive effects that some system parameters can have on the EMG signal. The phenomenon of crosstalk is used as an example of these problems. The review describes the limitations of techniques used to infer the level of muscle activation, the type of motor unit recruited, the upper limit of motor unit recruitment, the average discharge rate, and the degree of synchronization between motor units. Although the global surface EMG is a useful measure of muscle activation and assessment, there are limits to the information that can be extracted from this signal.

The extraction of neural strategies from the surface EMG

Electrodiagnostic criteria for diagnosis of ALS.

Propagation velocity in human muscle fibers in situ

The findings of the recently developed technique of Macro EMG in healthy subjects of different ages are described. The characteristics of the Macro motor unit potential which probably reflects the relative size of the whole motor unit are presented together with suggested normal data for the three muscles studied. An increase in size of the Macro motor unit potential was found with age, particularly after the age of 60 years. Possible factors determining the Macro EMG signal and the age related changes are discussed.

https://jnnp.bmj.com/content/jnnp/45/10/870.full.pdf

Macro EMG in healthy subjects of different ages.

SummaryThe physiology of the motor unit potential (MUP) is reviewed. The aim is to identify the electrophysiological events in the motor unit that generate the individual parts of the MUP. This is based on insight gained from new experimental techniques, such as single-fiber electromyography (EMG),

Quantitative analysis of individual motor unit potentials: a proposition for standardized terminology and criteria for measurement.

Single fibre electromyography

A new electromyographic technique for the study of the motor unit is described. A modified single fibre EMG electrode is used. The electrical activity obtained by the electrode shaft during voluntary muscle contraction is averaged after triggering from a single muscle fibre action potential and the contribution from one motor unit is thus extracted. This "Macro EMG" signal gives information about the whole motor unit in contrast to the regional or focal electrical activity measured by conventional or single fibre EMG recordings, respectively.

https://jnnp.bmj.com/content/jnnp/43/6/475.full.pdf

Erik Stålberg

Papers

Propagation velocity in human muscle fibers in situ

Macro EMG in healthy subjects of different ages.

Quantitative analysis of individual motor unit potentials: a proposition for standardized terminology and criteria for measurement.

Single fibre electromyography

Macro EMG, a new recording technique.