Physiological and architectural changes in the ageing muscle and their relation to strength and function in sarcopenia

In the ageing muscle, many changes occur. Some are on an architectural level, like alterations in muscle composition, or modifications in the characteristics of the muscle fiber itself, where muscle fiber length, orientation and type change. Other changes are neuronal, which occur on all levels, from the central activation over the spinal properties down to the level of the motor unit and the neuromuscular junction. There are also hormonal factors that undergo agerelated concentration variations. All these alterations in the muscle have an effect on both strength and function. In this matter, they contribute to the process of sarcopenia. Although many different components are identified, it is still unclear to what degree these components contribute to the loss of muscle mass, strength and function. This review summarizes the occurring physiological and anatomical changes within the ageing muscle and links them to outcomes such as strength and function.