Moving Standard Deviation of Trunk Acceleration as a Quantification Index for Physical Activities: Validation Study

Area of Science:

• Biomedical Engineering
• Rehabilitation Science
• Wearable Technology

Background:

• Step count, a common physical activity metric, faces challenges with irregular gait and is inapplicable to wheelchair users.
• Existing device-specific measures lack cross-applicability.
• Moving standard deviation of acceleration (MSDA) from trunk movements is proposed as a universal physical activity metric.

Purpose of the Study:

• To evaluate the validity and feasibility of MSDA for quantifying physical activity in stroke patients.
• To compare MSDA with traditional step count in individuals with varying mobility levels.

Main Methods:

• 197 stroke hemiparesis patients were enrolled.
• Trunk movement MSDA and step count were measured using the hitoe smart clothing system.
• Participants were categorized by Functional Independence Measure (FIM) mobility levels (walking vs. wheelchair use).

Main Results:

• A strong correlation (r=0.78) was found between MSDA and step count, robust across walking and wheelchair groups.
• MSDA showed a normal distribution across mobility subgroups, unlike step count which exhibited a floor effect in wheelchair users.
• Median MSDA values correlated with FIM mobility scores, reflecting functional independence.

Conclusions:

• MSDA is a valid and feasible measure of physical activity for stroke patients, regardless of mobility status.
• MSDA demonstrates broad utility in rehabilitation, particularly for individuals with motor impairments like wheelchair users.
• This metric offers a more inclusive approach to physical activity assessment compared to step count.