Anatomical and principal axes are not aligned in the torso: Considerations for users of geometric modelling methods.

The accuracy and accessibility of methods to calculate body segment inertial parameters are a key concern for many researchers. It has recently been demonstrated that the magnitude and orientation of principal moments of inertia are crucial for accurate dynamic models. This is important to consider given that the orientation of principal axes is fixed for the majority of geometric and regression body models. This paper quantifies the effect of subject specific geometry on the magnitude and orientation of second moments of volume in the trunk segment. The torsos of 40 male participants were scanned using a 3D imaging system and the magnitude and orientation of principal moments of volume were calculated from the resulting geometry. Principal axes are not aligned with the segment co-ordinate system in the torso segment, with mean Euler angles of 11.7, 1.9 and 10.3 in the ZXY convention. Researchers using anatomical modelling techniques should try and account for subject specific geometry and the mis-alignment of principal axes. This will help to reduce errors in simulation by mitigating the effect of errors in magnitude of principal moments.

3D surface-imaging for volumetric measurement in people with obesity.

BACKGROUND: Current methods for tracking the progress of people with obesity towards a weight loss goal appear simple and potentially misleading. A technique to quantify change in body shape whilst visualising areas of the body where weight loss occurs would be advantageous, and has the potential to be used as a motivational tool. Three-dimensional (3D) surface-imaging would serve as a good basis for such a technique, however current systems are prohibitively expensive. OBJECTIVE: Highlight the use of a cheaper alternative 3D surface-imaging system for volumetric measurement in people with obesity. METHODS: A recently developed low-cost 3D surface-imaging system was used, having previously being validated in a healthy population. A total of 61 people with obesity, enrolled on a weight-loss programme, were surface-imaged using the system. RESULTS: The findings suggest the low-cost system can obtain 3D surface-images of an obese human body, from which numerical parameters could be calculated and further analysis conducted. CONCLUSIONS: Further studies will focus on the validity and reliability of such analyses and the potential of the system to be considered as a long-term instalment in primary healthcare settings as a weight loss aid.

Assessment of a Microsoft Kinect-based 3D scanning system for taking body segment girth measurements: a comparison to ISAK and ISO standards.

Use of anthropometric data to infer sporting performance is increasing in popularity, particularly within elite sport programmes. Measurement typically follows standards set by the International Society for the Advancement of Kinanthropometry (ISAK). However, such techniques are time consuming, which reduces their practicality. Schranz et al. recently suggested 3D body scanners could replace current measurement techniques; however, current systems are costly. Recent interest in natural user interaction has led to a range of low-cost depth cameras capable of producing 3D body scans, from which anthropometrics can be calculated. A scanning system comprising 4 depth cameras was used to scan 4 cylinders, representative of the body segments. Girth measurements were calculated from the 3D scans and compared to gold standard measurements. Requirements of a Level 1 ISAK practitioner were met in all 4 cylinders, and ISO standards for scan-derived girth measurements were met in the 2 larger cylinders only. A fixed measurement bias was identified that could be corrected with a simple offset factor. Further work is required to determine comparable performance across a wider range of measurements performed upon living participants. Nevertheless, findings of the study suggest such a system offers many advantages over current techniques, having a range of potential applications.