Proceedings of The Physiological Society
University of Manchester (2010) Proc Physiol Soc 19, PC73
Is balance worse when exposed to height?
M. C. Tersteeg1, D. E. Marple-Horvat1, I. D. Loram1
1. Institute for Biomedical Research into Human Movement and Health, Manchester Metropolitan University, Manchester, United Kingdom.
It is known that gait changes occur when people walk at height. It is unknown whether these reflect actual reduction in balance ability. Here we investigate evidence from muscle activity to evaluate the hypothesis that balance is worse when standing at height and to investigate if there is a habituation effect. Greater muscle activity for the same task could be seen as indicating reduced balance ability. Eighteen healthy adults performed a series of walking and one-legged stance tasks on 4.8m long walkways placed on the ground and at 3.06m off the ground. Here we report the one-legged stance tasks performed at 4 different locations (i) platform area away from edge (ii) platform edge in front of a 22 cm wide walkway, (iii) ¼ of the walkway, (iv) ¾ of the walkway. Tasks were performed walking out towards the open end of the walkway and walking back. EMG was recorded from the Tibialis Anterior (TA), Gastrocnemius (GAS), Soleus (SOL), Rectus Femoris (RF), Vastus Lateralis (VL) and Hamstring (HAM). Galvanic skin conductance (GSC) was recorded continuously during the experiment. A 4x2x2 repeated measure ANOVA with the factors location, direction (going out vs back) and condition (ground vs height) was performed for all muscles and for GSC. Overall muscle activity was increased during one-legged stance on the high walkway compared to the ground and was dependent upon location. Muscle activity was highest on ¼ of the walkway at height. GAS, TA, RF and VL muscles indicate that activity was lower for the tasks on the way back compared to the tasks on the walk out. Also, GSC was higher at height compared to the ground level and dependent upon location. GSC was highest on the ¼ of the walkway at height, while there was no difference at ground level. See table for summary of the statistical results. Judging balance with muscle activity as parameter suggests that balance ability is reduced at height and more at some locations than others. It has been shown that the altered visual information is not responsible for the changes in gait at height (1) and since arousal also shows an effect of height and location this suggests a more general change in the body underlies the increase in muscle activity such as a change in motor set which could interfere with normal control of balance. The effect of direction indicates that either habituation occurs or a difference in perception of the task facing the open end or the platform. This requires further investigation.
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