If we consider a population of free-living individuals, who are 65 years old and even older, a substantial proportion (in the range of 6% to 25%) suffers from many of the elements of the syndrome of frailty. Although the syndrome is complex and still lacks a standard definition, there is a growing consensus about its signs and symptoms. Patients who are afflicted with frailty typically exhibit losses of muscle strength, fatigue easily, are physically inactive, with an increased risk (and fear) of falling, have undergone a recent, unintentional loss of weight, experience impaired cognition and depression, all of which is frequently complicated by a variety of coexistent illnesses. In this context, functional tests to predict disability and frailty are needed. Accelerometry offers a practical and low cost method of objectively monitoring human movements, and has particular applicability to the monitoring of disability in an aging population. Accelerometers have been used to monitor a range of different movements, including gait, sit to stand transfers and postural sway. This review focuses on methodological concepts in the evaluation of skeletal muscle function and monitoring systems (accelerometers and gyroscopes) in each of these areas. An integrated approach is described in which a combination of accelorometry and gyroscopy can be used to monitor a range of different parameters (muscle power, gait and balance) in an aging population in a clinical or out-patient setting.