Validity of estimated relative angular information obtained using an inertial motion capture system during standing trunk forward bending

Kazuhiro Ishida, Takahiko Hyakumachi, Taiki Morikawa, Hiroshi Katoh
Purpose:

This study aimed to validate the estimated angular information obtained from the MS during forward bending at comfortable and maximum speeds, using the 3DMA system as a reference.

Methods:

Twelve healthy older men were recruited. A 3DMA system and five MS were used for the measurements. The infrared markers were attached to each MS. The MS were attached with double-sided tape to the first thoracic spinous process (T1), seventh thoracic spinous process (T7), first lumbar spinous process (L1), third lumbar spinous process (L3), and second sacrum spinous process (S2). The upper thoracic (UT) was defined between T1 and T7, lower thoracic (LT) was defined between T7 and L1, upper lumbar (UL) was defined between L1 and L3, and lower lumbar (LL) was defined between L3 and S2. The task was forward bending, and it was performed at two different speeds (comfortable and maximum speed). The analyzed parameters encompassed angle and angular velocity, range of motion (ROM), and waveform. The Euler angles were rotated in the order of the XYZ axes using the 3DMA system were used. The estimated angles were obtained directly from the MS angle. The angle was defined as 0° when the MS was perpendicular to the ground. Angular velocity was used the maximum value obtained from the MS. ROM was defined as the amount of change from 0° at the initiation of movement to the maximum angle. The waveform was defined as the time-series data from the start to the end of the task. The agreement of angles in the ROM was assessed using the intraclass correlation coefficient (ICC) (2,3). The error between two angles was validated using the mean absolute error (MAE). The congruence of waveforms for the two angles was examined using the coefficient of multiple correlation (CMC).

Results:

At comfortable speed, the maximum angular velocity was −104 ± 22.4°/s. ICC (2,3) was >0.9. MAE was 1.7° (UT), 1.4° (LT), 1.4° (UL), and 0.8° (LL). CMC was >0.9. At maximum speed, the maximum angular velocity was −200.3 ± 36.2°/s. ICC (2,3) was >0.9. MAE was 1.9° (UT), 1.0° (LT), 1.5° (UL), and 3.0° (LL). CMC was 0.86 (UT), 0.99 (LT), 0.96 (UL), 0.98 (LL).

Conclusion(s):

The study shows high agreement of angles between Euler and MS, with a maximum error of 3.0°. Thus, the validity of forward bending assessment using MS is high.

Implications:

MS is wearable devise and can be used at anywhere. Therefore, MS can be used in rehabilitation.

Funding acknowledgements:
There was no funding for this study.
Keywords:
motion sensor
validity
motion velocity
Primary topic:
Musculoskeletal: spine
Did this work require ethics approval?:
Yes
Name the institution and ethics committee that approved your work:
Eniwa Hospital Ethics Committee
Provide the ethics approval number:
195
Has any of this material been/due to be published or presented at another national or international conference prior to the World Physiotherapy Congress 2025?:
No

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