Physiological Changes Associated with Aging and Immobility

Aging, an inevitable and extremely complex, multifactorial process, is characterised by the progressive degeneration of organ systems and tissues. It is largely determined by genetics, and influenced by a wide range of environmental factors, such as diet, exercise, exposure to microorganisms, pollutants, and ionising radiation. This explains why two people of the same age may differ markedly in terms of both physical appearance and physiological state. Gender also plays a part and, in most developed countries, women typically outlive men by 7–10 years [1]. Recent research has also demonstrated that distant experiences such as childhood personality and education, as well as behavioural factors, also contribute to longevity [2]. It is generally accepted that the aging process falls physiologically into three groups of changes that occur with advancing age [3]. The first group encompass changes in cellular homeostatic mechanisms, for example, body temperature, blood, and extracellular fluid volumes; the second group are related to a decrease in organ mass; the third and possibly the most important group of changes, in terms of their impact, involve a decline in and loss of the functional reserve of the body’s systems. Loss of these functional reserves may impair an individual’s ability to cope with external challenges such as surgery or trauma. Maintaining physiological function (health) in an aging population is of prime importance not only to the well-being of the aging individual, but also from a social perspective, helping to reduce the burden on medical services and systems [4]. It has also been long established that the physiological changes associated with normal aging are mirrored during periods of immobility, such as prolonged hospital bed rest, or after a fractured limb or a fall. It was with the above in mind and with the hope of collating research and knowledge examining the effects of normal aging and immobility that we developed the call for this special issue. Three of the seven papers in the Issue discuss physiological changes in muscle tissue: