Determinants of musculoskeletal frailty and the risk of falls in old age.

Neuromuscular parameters that describe locomotion are indispensable variables for the diagnosis and treatment of frailty, fall risk and osteoporosis. A scientifically-based standardized locomotor assessment should be an essential part of medical examinations in research and clinical practice. There has been no previous consensus regarding which test procedures should be included in a locomotor assessment. The goal of this article is to provide a rationale for the selection of appropriate locomotor tests in a comprehensive locomotor assessment for elderly patients. We propose that a locomotor assessment should comprise the parameters that have been proven predictive for both falls and impending disability. The parameters should be measured in the standard units of physics. Therefore, we propose the following tests for a standardized locomotor assessment: (1) Self-selected gait velocity as the single best measure of general locomotor status and a good predictor of age-related adverse events; (2) Chair rise test (timed 5 chair rises) which measures power on vertical movement and the hip surrounding muscles as the most important neuromuscular risk factor for falls and fall-related fractures; (3) Tandem standing and tandem walking to measure postural capacity (balance) to the side; (4) Timed up and go test as a global screening procedure; (5) Clinical gait analysis with special focus on regularity; and (6) At least on a research level, movement must be measured referring to the terms of physics by mechanography. Mechanography (Leonardo force plate system, Novotec Pforzheim, Germany) records the time course of ground reaction forces, velocity of the vertical movements of the center of mass and power during unrestricted physiological movements. In the mechanogram the eccentric and concentric phases of movements can be differentiated and the storage of energy in the elastic elements of the body can be examined. The kinetics of human movement is explained by mechanograms of a two-legged jump. The ground reaction forces resulting from a jump down from a height of 0,46 m are demonstrated as a performance that is representative for human coordination. One goal of this text is to underline the insights that arise if the rules of physics are applied to human movement. A deeper understanding enables us to create more effective treatments for disorders of the muscle-bone unit. Bringing physics and cybernetics into the field of osteoporosis is a great heritage of Harold Frost.