Fukui T1, Otake Y1
1Bunkyo Gakuin University, Graduate School, Health Care Science, Tokyo, Japan
Background: Pelvic drop during ambulation is thought to increase knee adduction moment. Similarly, spinal posterior alignment may be related to knee flexion posture. These relationships may help to retain upper and lower body equilibrium. In addition, a hip strategy maintains the center of mass (COM) through opposing motion between the upper and lower body. COM has been analyzed using multi-segmental models. Mechanical assessments of each segment, including mass and inertia, have been based on cadaver studies. As upper and lower body densities are different, conventional methods have limited ability to examine opposing motion between upper and lower bodies with equal mass. Using COM coordinates and virtual upper [UM] and lower [LM] body COM with equal mass may provide useful information during clinical observation. These parameters have not been previously studied.
Purpose: This study aimed to precisely localize upper and lower body COM and to investigate opposing motion as a hip strategy.
Methods: Nine healthy subjects aged between 21 and 45 years volunteered for this study. Thirty-nine markers were attached to each subject and images were captured using a 3-dimensional motion analysis system with 12 MX cameras. The 3-dimensional coordinates of each marker were analyzed using a plug-in gait model [PIG]. Five virtual markers were assigned to UM [U1-U5] and 5 were assigned to LM [L1-L5], as follows. U1 was defined as the midpoint between the C7 spinous process and center of the clavicles. U5 was defined as the midpoint between the xiphoid process and T10 spinous process. U2, U3, and U4 were on the line connecting U1 and U5, at 25%, 50%, and 75% of the distance from U1, respectively. L1 was defined as the midpoint of both hip centers. L5 was defined as the midpoint between knee centers. L2, L3, and L4 were on the line connecting L1 and L5, at 25%, 50%, and 75% of the distance from L1 respectively. The COMs derived from UM and LM were defined as the midpoints of combinations of each of 5 coordinates as 25 variables. The COMs derived from virtual markers were compared to COMs calculated using PIG to determine the optimal combination. Subjects performed forward bending, backward bending, squatting, and walking at a self-selected speed. Two trials were performed for each subject. All study participants provided written informed consent. Approval was obtained from the Ethics Committee of Bunkyo Gakuin University [No. 2016-0022].
Results: In all motion analyses, the optimal combination of COM using virtual markers and COM using PIG was U4 and L3 [25.9±14.6 mm/frame]. The second-best combination was U3 and L3 [27.5±14.9 mm/frame].
Conclusion(s): The difference between COM using virtual markers and COM using PIG was considered small enough to use under clinical conditions.
Implications: Use of U1 and L1 can aid in clinical assessment and subsequent treatment with methods such as trunk exercises for lower extremity disorders. UM moved in a direction opposite to that of LM during forward bending, backward bending, and squatting in the sagittal plane. In stance phase, LM often showed movement opposite to that of UM in the frontal plane.
Keywords: biomechanics, Center of mass, hip strategy
Funding acknowledgements: NONE
Purpose: This study aimed to precisely localize upper and lower body COM and to investigate opposing motion as a hip strategy.
Methods: Nine healthy subjects aged between 21 and 45 years volunteered for this study. Thirty-nine markers were attached to each subject and images were captured using a 3-dimensional motion analysis system with 12 MX cameras. The 3-dimensional coordinates of each marker were analyzed using a plug-in gait model [PIG]. Five virtual markers were assigned to UM [U1-U5] and 5 were assigned to LM [L1-L5], as follows. U1 was defined as the midpoint between the C7 spinous process and center of the clavicles. U5 was defined as the midpoint between the xiphoid process and T10 spinous process. U2, U3, and U4 were on the line connecting U1 and U5, at 25%, 50%, and 75% of the distance from U1, respectively. L1 was defined as the midpoint of both hip centers. L5 was defined as the midpoint between knee centers. L2, L3, and L4 were on the line connecting L1 and L5, at 25%, 50%, and 75% of the distance from L1 respectively. The COMs derived from UM and LM were defined as the midpoints of combinations of each of 5 coordinates as 25 variables. The COMs derived from virtual markers were compared to COMs calculated using PIG to determine the optimal combination. Subjects performed forward bending, backward bending, squatting, and walking at a self-selected speed. Two trials were performed for each subject. All study participants provided written informed consent. Approval was obtained from the Ethics Committee of Bunkyo Gakuin University [No. 2016-0022].
Results: In all motion analyses, the optimal combination of COM using virtual markers and COM using PIG was U4 and L3 [25.9±14.6 mm/frame]. The second-best combination was U3 and L3 [27.5±14.9 mm/frame].
Conclusion(s): The difference between COM using virtual markers and COM using PIG was considered small enough to use under clinical conditions.
Implications: Use of U1 and L1 can aid in clinical assessment and subsequent treatment with methods such as trunk exercises for lower extremity disorders. UM moved in a direction opposite to that of LM during forward bending, backward bending, and squatting in the sagittal plane. In stance phase, LM often showed movement opposite to that of UM in the frontal plane.
Keywords: biomechanics, Center of mass, hip strategy
Funding acknowledgements: NONE
Topic: Human movement analysis
Ethics approval required: Yes
Institution: Bunkyo Gakuin University
Ethics committee: Department of Health Science Technology
Ethics number: No. 2016-0022
All authors, affiliations and abstracts have been published as submitted.
