Postural sway during single-legged standing is dependent on the body position assumption strategy and supports the stability and mobility trade-off hypothesis

Studies that would address the problem of balance in the context of either the preceding or subsequent movement are scarce. We would like to propose the inverse relationship between stability and mobility as a general principle and that depending on the preceding action the postural sway characteristics in quiet standing would significantly differ. Thirteen female ballet school students were examined. Their mean age was: 15.1{+/-}0.95 years and the total of about 2500 (5th school grade) and 4200 (6th school grade) hours of dance training. The force plate was used to register ground reaction forces and moments. During the 30s trials subjects were to assume the Passe position in gait initiation (G-I) and gait termination (G-T) task condition. The following parameters were analyzed after restabilisation point estimation: the range of COP position, standard deviation of COP position, mean velocity in both planes and mean resultant velocity. The results showed significant differences between the G-I and G-T tasks in postural sway characteristics and confirmed our hypothesis. The practical implication of our study is the way of preparation to test position (PTTP) strategy might be as important as the measurement itself in the posture study protocols.