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Session: Poster session I
Session starts: Thursday 24 January, 15:00

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Lizeth Sloot (VU university medical center Amsterdam)
Marjolein van der Krogt ()
Jaap Harlaar ()

Abstract:
Gait research increasingly involve instrumented treadmills, since they offer new experimental possibilities and simplify continues measurement. However, walking on a treadmill is known to effect gait performance, presumably due to the imposed walking speed. A feedback-controlled treadmill that follows so called self-paced walking would be a good alternative to allow for small, natural variation in walking speed. The purpose of this study was to compare the effect of different self-paced (SP) walking algorithms on spatiotemporal parameters, joint kinematics and kinetics, and compare the effect of SP versus fixed speed (FS) treadmill walking. Eighteen healthy subjects (12 male, age 29±4) walked on a dual-belt instrumented treadmill in a speed-matched virtual environment (Gait Real-time Analysis Interactive Lab (GRAIL), Motek Medical B.V., the Netherlands). During SP, the treadmill speed was regulated by a PD controller, with velocity dependent gains with additional correction for sudden slowing down (SP1), a standard PD controller with the same correction (SP2), and a PD controller with position dependent differential gain and improved correction for deliberate de- and acceleration (3). After 10 minutes of habituation, subjects walked for three minutes at SP1 and speed-matched FS, followed by SP walking in each mode in random order. A Vicon system measured 25 markers and joint kinematics were calculated following the HBM model. For each subject, both the mean stride and stride variation were calculated. The difference in joint kinematics or kinetics were expressed as the average offset or gain and the offset or gain corrected root mean square (RMS) value, thus indicating a difference in pattern. The effect of SP-mode was evaluated using an ANOVA, whereas SP and FS were compared with paired t-tests. Variance of walking speed as well as stride length were slightly decreased in the SP2 mode (p=0.03 and p=0.01), whereas kinematics and kinetics were comparable between modes. During SP, walking speed varied considerably over time (p<0.001), while mean stance percentage was slightly reduced (p<0.001). There were no relevant differences in kinematics or kinetics between SP and FS treadmill walking. The results show that gait performance was relative insensitive for the specific SP mode, although it seems that the altered PD controllers (SP1 and SP3) allow for more variability in walking speed. This walking variability was also increased compared to constraint FS walking, whereas other gait measures did not show relevant significant differences. Therefore, SP walking seems a good experimental alternative to simulate over ground walking in clinical gait analysis. Additionally, the application of SP allows for studying fatiguing and pathological gait variability. Further research should focus on whether SP better resembles over ground walking than FS treadmill walking.