Abstract
Water, the main component of the body, is distributed in the extracellular and intracellular compartments. Water exchange between these compartments is mainly governed by osmotic pressure. Extracellular water osmolarity must remain within very narrow limits to be compatible with life. Older adults lose the thirst sensation and the ability to concentrate urine, and this favours increased extracellular osmolarity (hyperosmotic stress). This situation, in turn, leads to cell dehydration, which has severe consequences for the intracellular protein structure and function and, ultimately, results in cell damage. Moreover, the fact that water determines cell volume may act as a metabolic signal, with cell swelling acting as an anabolic signal and cell shrinkage acting as a catabolic signal. Ageing also leads to a progressive loss in muscle mass and strength. Muscle strength is the main determinant of functional capacity, and, in elderly people, depends more on muscle quality than on muscle quantity (or muscle mass). Intracellular water content in lean mass has been related to muscle strength, functional capacity, and frailty risk, and has been proposed as an indicator of muscle quality and cell hydration. This review aims to assess the role of hyperosmotic stress and cell dehydration on muscle function and frailty.
Highlights
Water is the main component of the body and represents approximately 76% of muscle mass.With ageing, there is a progressive decline in total body water (TBW) and intracellular water (ICW)parallel to an age-related loss of muscle mass and muscle strength
Intracellular water content in lean mass has been related to muscle strength, functional capacity, and frailty risk, and has been proposed as an indicator of muscle quality and cell hydration
This review aims to assess the role of hyperosmotic stress and cell dehydration on muscle function and frailty
Summary
Water is the main component of the body and represents approximately 76% of muscle mass. ICW determines cell volume and is believed to affect its metabolism, as water affects protein structure and enzymatic activity. ICW content in lean mass has been proposed as an indicator of muscle quality and cell hydration and has been related with strength, functionality, and frailty. (4) A structural boundwithin to cytoplasmic proteins determines cell volume, which, in water keeps function. Water is the solvent in the human body in which different solutes such as ions, proteins and other molecules are dissolved. The concentrations of these solutes are different between the intracellular and extracellular spaces and should be maintained within a small range of variation. The volume of the extracellular compartment (plasma and interstitium) depends mainly on total body sodium and the accompanying anions (mainly chloride and bicarbonate), since these constitute 90–95% of the total of osmotically active particles in extracellular fluid [9,16]
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