INTRODUCTION:​ Instrumented treadmills are becoming increasingly more common in gait laboratories. Instrumented side-split treadmills allow the collection of forces under each foot during walking. However, there may be a tendency to increase the base of support when walking on these treadmills, influencing other frontal plane mechanics as well. Therefore, the purpose of this study was to examine the effect of walking on a side-split instrumented treadmill on base of gait and frontal plane kinematics of the lower extremity.

METHODS:​ Twenty subjects walked on both a split and a single-belt treadmill for 10 minutes each. Base of gait and frontal plane kinematic angles and variability data were recorded. A two-factor repeated measures ANOVA (belt condition x time) was used to identify any differences between the two conditions, as well as over the 10 minute accommodation period. The relationships between the change in base of gait and change in each kinematic variable were also determined.

RESULTS:​ No significant interactions were found, thus only main effects were assessed. On average, the base of gait was 3.9 cm wider on the split-belt treadmill. A significant, but small (0.4°) reduction was seen in knee adduction, and no difference was seen in hip or rearfoot frontal plane kinematics on the split-belt condition. In terms of correlations, the increase in base of gait was significantly related to a decrease in peak knee and hip adduction angles. Base of gait variability was significantly reduced on the split-belt condition. In contrast, hip adduction variability was significantly increased.

CONCLUSION:​ The 4 mm gap between the treadmill belts significantly increased the base of gait in all subjects. However, this had a negligible effect on the other lower extremity kinematics.