Mobility Lab v1 and Mobility Lab v2 use different approaches for estimating the various measures of gait. Here is a brief rundown of the main differences:
Mobility Lab v1:
- Sensors are placed on the shanks (shins), and only the gyroscope is used.
- Spatial characteristics (e.g., stride length) are determined from bio-physical modeling such as an inverse pendulum model. These calculations embed a number of assumptions, and may introduce error when these assumptions are not true for a particular subject.
Mobility Lab v2:
- Sensors are placed on the top of the feet.
- A complex fusion of the accelerometer and gyroscope are used, along with an approach called "zero-velocity updates", to track the trajectory of each foot through 3D space.
- Spatial characteristics (e.g., stride length) are measured from the foot's trajectory, as opposed to a bio-physical model. These have been shown to be more accurate when compared to video motion capture and gait mat "gold standards".
- A number of additional measures can be calculated, such as the heel-strike angle, the elevation of the foot at midswing, and the circumduction of the foot during a step.
Is there a validation study that shows these differences?
We are currently engaged in a thorough validation study which compares the gait measures obtained from:
- Video Motion Capture
- A GaitRite gait mat
- Mobility Lab v1
- Mobility Lab v2
This study is not yet complete, but will be linked to from this article when it is.
Attached, however, is an journal publication by a 3rd party group who performed an similar, independent validation of our system. They found that "the IMU system in this study appears to be both accurate and repeatable for measuring spatiotemporal gait parameters in healthy young adults" and that "the foot configuration of the IMUs appeared to better measure gait parameters".
Can I compare Mobility Lab v1 and v2 results?
While both products calculate many of the same measures, direct comparison between the two versions of Mobility Lab is not recommended. Most of the measures are highly correlated, but there may be be biases associated with the respective method. In addition, some of the measures, such as stride length, are measured quite differently. For longitudinal studies, it is recommended that you stick with one approach or the other.