The results showed that gyroscopes could be placed anywhere along the same plane on the same segment giving an almost identical signal. The gyroscopes can therefore be attached to a convenient position which might avoid areas of skin and muscle movement.
93K. Tong, M.H. Granat/Medical Engineering & Physics 21 (1999) 87–94
Fig. 8. Knee angle in a normalised gait cycle calculated from the gyroscopes on the shank and thigh segments. The vertical lines mark the heel strike (HS), foot flat (FF), heel off (HO) and toe off (TO). The dotted line is the angle in each gait cycle and the solid line is the average value.
For a practical portable motion analysis system, first it is useful to be able to analyse walking during turning (e.g. walking along a figure-of-eight path) and second it maybe desirable to collect data from several straight line walks without having to reset the system each time the subject changes direction. We have identified that there is a significant problem with the derived signals from gyroscopes if the subject changes direction or turns (Figs. 6 and 7). This is due to the limited information content from the signal of a uni-axial gyroscope. This could have been solved by using a tri-axial gyroscope, however this would have increased the size, complexity and cost of the system. More complex equations are required to calculate the orientation of the segment. The drift problem during turning was removed successfully using either automatic reset in each gait cycle or highpass filtering. If foot contact information is available from the gait analysis system, then a gyroscope can be automatically reset for every step.