The Role of Water Homeostasis in Muscle Function and Frailty: A Review

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.

AQP1 modulates tendon stem/progenitor cells senescence during tendon aging

“…Altered expressions or functions of AQPs lead to fluid loss, and this loss is closely associated with cell aging 15 . Furthermore, AQPs can also facilitate the diffusion of reactive oxygen species, which lead to cellular alterations related to cell aging 15,27 . Studies have showed that functional AQP1 is inserted into the plasma membrane 28,29 .…”

The time course of calf muscle fluid volume during prolonged running

“…The fluid exchange between extramuscular and intramuscular compartments is a complex interplay between hydrostatic and osmotic forces, governed by anatomical and biochemical factors (Lorenzo et al, 2019; Senay & Pivarnik, 1985; Sjogaard & Saltin, 1982). In line with previous literature, we found a rapid initial increase of ACSA with the onset of exercise after 2.5 min of running.…”

“…Water is an essential component of the human body with important metabolic, transport, temperature control, structural, and mechanical functions (Lorenzo, Serra‐Prat, & Yébenes, 2019). In skeletal muscle, for example, fluid flows are crucial in the regulation of ion concentrations and pH, which affect muscle contraction and hence force development during exercise (Sjogaard & Saltin, 1982).…”

Dose-response relationship between protein intake and muscle mass increase: a systematic review and meta-analysis of randomized controlled trials

“…The results demonstrated that the intake of additional amounts of protein of as little as around 5 g/day, resulted in an unadjusted average increase in lean body mass of about 500 g, and on adjusting for confounding factors, an average increase in lean body mass of about 1200 g was seen. Water accounts for about 76% of muscle, 20 and considering that 80% of the dry weight is made up of protein, the amount of muscle protein assimilated during the intervention period is estimated to be approximately 240 g (multivariate-adjusted model results). Since in those studies with protein interventions of < 10 g/day energy balance was not negative in all subjects, if 5 g/day of supplementary protein was digested and absorbed at an absorption rate of 81%, 21 it takes approximately 59 days (eight weeks), assuming that all absorbed amino acids are used in increasing lean body mass.…”