Effects of healthy aging on balance : a quantitative analysis of clinical tests

Sammanfattning: Introduction: Physical therapists employ various tests to assess balance in elderly individuals, but few of these provide adequate information concerning the aspect of balance or postural control that is being measured or the reason for any decline in performance. Furthermore, tools for assessment of balance should serve as a basis for adequate intervention. In connection with attempts to understand the effects of healthy aging on balance, the first step is to define changes in postural control mechanisms that may result in deficient balance or a fall in elderly individuals. Objectives: The aim of the present thesis work was to apply and evaluate three clinical tests i.e., functional reach (FR), one-leg stance (OLS) and tandem stance (TS) to determine the effects of healthy aging on balance. Identification of exactly what is being measured in healthy young and elderly adults by these tests was an additional major goal. Methods: Thirty-three healthy elderly individuals (65-80 years of age) and 30 healthy 25-40-year-old adults performed FR, OLS and TS while standing on force plates, which allowed forces, movement and muscle activity to be monitored in parallel with the clinical parameters. In addition, in Study IV initiation of gait was examined in this same manner. Results: Our findings provide evidence that healthy aging has a deleterious influence on postural control. Age-related differences were observed in the amplitude of postural steadiness during performance of OLS and TS; in the timing of the force peak during the weight transfers involved in OLS, TS and initiation of gait; as well as in the distribution of body weight between the legs prior to performance of the tasks. During FR, healthy elderly subjects exhibited a low degree of correlation between stability limits and reach distance (r=0.38) and a moderate correlation between forward trunk bending and reach distance (r=0.68). In connection with OLS and TS, two phases occurred in both the elderly and younger groups: an initial dynamic phase involving a reduction in force variability during the first 3-5 seconds, followed by a static phase during which a certain constant level of force variability was maintained. Moreover, both groups supported more weight on the rear leg during TS. Conclusion: Altogether, the findings documented here indicate that the aging process in itself has a deleterious influence on balance. Healthy elderly individuals utilize a compensatory strategy in connection with FR, which results in low concurrent validity. In general, this work provides insight concerning not only how elderly and younger individuals perform, but also exactly what is being measured by these balance tests. Clinical recommendations: Balance or postural control is influenced by a number of physiological systems, the functions of which are affected by aging. When applying the FR test, compensatory mechanisms should be taken into consideration. The first 5 seconds of OLS and TS provide the most important information. Tandem stance does not involve equal weight-bearing, so both legs should be tested in both positions. Finally, balance should not only be assessed solely on the basis of task parameters (e.g., number of centimeters or seconds), but also on how the task is performed.