# Absolute Reliability and Concurrent Validity of the Modified  
Gonometric Platform for Measuring Trunk Rotation in the  
Sitting Position  
Jianhong Gao  
Faculty of Educational Studies, University Putra Malaysia, Serdang 43400, Malaysia Research and Innovation Division, National Sports Institute of Malaysia, Kuala Lumpur 57000, Malaysia Institute of Sports Medicine and Rehabilitation, Shandong First Medical University, Ta'an 271000, China  
Jin Seng Thung  
Faculty of Educational and Sport, Charles University, 1625 Prague, Czech Republic  
[PERSON]  
Sept. 202220220220220220220220220220220220220220220220220220222022022022202220222022202220222022220222202222022220222202222  
in the literature. A commonly accepted definition is the cross angle between the line of both anterior superior iliac crests and the line of both shoulders' acromion joints [8]. Another common definition is that the trunk rotation angle is measured by the angle changes of the line from the first thoracic vertebrae (T1) to the upper edge of the sacrum [4]. Three-dimensional (3D) motion analysis systems, three-dimensional magnetic resonance imaging (3D-MRI), two-dimensional video analysis, inclinometers, and goniometers have been developed to measure trunk rotation in different positions based on different definitions of trunk rotation. As a result, various protocols have been used to measure trunk rotation in different positions, such as upright standing, trunk flexion, sitting, and prone lying [5; 9; 10; 11]. However, due to its structural complexity, there is no standard method for measuring trunk rotation.  
3D motion analysis and 3D-MRI are costly instruments that require specific space and professional skill requirements [9; 12]. Although these two devices are accurate, they are not the first considerations for measuring trunk rotation due to their complexity and price. Two-dimensional (2D) video analysis is a reliable and valid tool for measuring trunk rotation in the transverse plane. However, this device is relatively expensive, and moderate skill is required due to the additional matched software needed to analyse its data [13]. In contrast, goniometers and inclinometers are the least expensive instruments [14]. In a previous study, double inclinometers were separately placed onto the spinous process of the seventh cervical vertebra and sacral vertebra to measure trunk rotation in the standing position with a 90-degree trunk flexion. This position is challenging for a person with poor balance control [15]. A goniometer is a convenient portable device, but there are challenges associated with positioning and controlling the dynamic and fixed arms and identifying bony landmarks for users [16]. Thus, a more straightforward, portable, and inexpensive device for measuring trunk rotation is needed.  
The goniometric platform, as a novel tool, is easy-to-use and low-cost equipment used to assess trunk rotation in the sitting position, and it was initially used by [PERSON] et al. [17]. Although the goniometric platform has good-to-excellent reliability for measuring right (\(\alpha=0.80\)) and left (\(\alpha=0.96\)) trunk rotations, its validity has not been confirmed [17]. In addition, the previous goniometric platform did not sufficiently consider ergonomic effects. Participants reported that the goniometric platform restricted their ability to perform maximum trunk rotation because of the distance between the table and the seat, indicating the need for further improvements to the platform [17]. Thus, the reliability and validity of the modified goniometric platform to measure trunk rotation in the sitting position required further investigation.