Body movements during postural stabilization:measurements with a motion analysis system

Abstract Good postural stability is needed during most activities in daily life. Balance can be improved with specific training programmes in physiotherapy. The goals of treatment differ, depending on the subject's age and disorders. In clinical practice, postural stability is commonly evaluated by scaled functional tests or by recording body sway on a platform. On the basis of therapeutic modalities, information of separate movements of body segments would be important. The data might be useful in developing balance evaluation and training programmes in physiotherapy. The aim of this project was to present one method and to estimate its reliability and validity in studying the movements of separate body segments in postural control. In addition, the association between age, gender and anthropometric factors and the movements of separate body segments during quiet stance with the eyes open and closed were studied in a group of healthy subjects. A method was developed to measure the body movements during standing with a motion analysis system, and the reliability of body movement measurements was evaluated. The validity of the motion analysis measurements was evaluated to compare the balancing body measurements during stance on two legs and on one leg obtained with a motion analysis system and a platform. In cross-sectional studies, 100 healthy randomly selected subjects were stratified into ten groups (by age and gender). The body movements of all subjects standing on two legs with the eyes open and closed were measured using a motion analysis system and calculated as maximal and total movements. The movement velocities and accelerations were analysed and compared between the eyes open and eyes closed conditions. The associations between movement values and age and gender were analysed. In addition, the body anthropometrics of the subjects were measured and the relations between the body characteristics and the body balancing movements were calculated using regression analysis. The results showed that motion analysis can be used in measuring body movements in postural stability. Better reproducible balance measurement results are obtained with the total movement values than with the maximal amplitude values. In a comparison of the parameters used in a validity study, motion analysis and platform seemed to reflect the same aspect of balance, although the views of measurement were different. During standing on two legs with the eyes open, there was a statistically significant difference in the maximal anterior-posterior head movement and in the vertical navel movement between the age groups, but the results did not show other statistically significant differences between the balancing movements of separate body segments of the groups or between the balance measurement values of men and women in standing on two legs with the eyes open and closed. It seems that healthy female and male subjects control their stance with quite similar ranges of body adjustment. Body characteristics had slight but considerable effects on the variations of body balancing movements in standing on two legs with the eyes open, but almost none in the eyes-closed conditions. There were differences in the results between the male and female groups. In standing on two legs with the eyes closed, all the measured body parts except the ankles had significantly higher maximal velocity and acceleration values than in standing with the eyes open. The effect of visual information on balancing the body seems to be essential. The results indicated that the motion analysis system is also a useful tool in further balance studies, but the methods of analysis need to be developed. Postural stability should be evaluated and practised even in more demanding balance performances. Movement speed and the special role of each body part in maintaining balance should be paid attention