Measurement device, measurement system, measurement method, and recording medium

A body dimension estimation method comprising:

• acquiring time-series data of sensor data measured by an inertial sensor arranged on footwear of a user, the time-series data including at least an acceleration and an angular velocity related to motion of a foot of the user;
• generating, from the time-series data, a gait waveform including a plantar angle of the foot and a trajectory of the foot in a traveling direction of the user;
• detecting, based on the gait waveform, gait events including at least a toe off and a heel strike in one gait cycle, and at least one of a consecutive heel strike or a consecutive toe off;
• calculating, based on the trajectory of the foot in the traveling direction at the detected gait events, a stride length corresponding to a movement distance of the foot in the traveling direction between the consecutive gait events;
• calculating, based on the plantar angle of the foot and a position of the inertial sensor at a timing of the heel strike and on a constraint condition that a lower leg of the user is substantially perpendicular to a ground at the timing of the heel strike, a distance between the inertial sensor and an ankle joint of the user;
• calculating, based on the stride length, the distance between the inertial sensor and the ankle joint, and on a geometric model on which constraint conditions related to motion of lower limbs of the user are imposed, a length of at least one segment of the lower limbs including at least one of a length of a lower leg between the ankle joint and a knee joint and a length of an upper leg between the knee joint and a hip joint;
• and
• outputting body dimension information including the calculated length of the segment of the lower limbs for use in control of a measurement or training support related to gait of the user.

A non-transitory computer-readable storage medium storing instructions that, when executed by a processor, cause the processor to:

• acquire time-series data of sensor data measured by an inertial sensor arranged on footwear of a user, the time-series data including at least an acceleration and an angular velocity related to motion of a foot of the user;
• generate, from the time-series data, a gait waveform including a plantar angle of the foot and a trajectory of the foot in a traveling direction of the user;
• detect, based on the gait waveform, gait events including at least a toe off and a heel strike in one gait cycle, and at least one of a consecutive heel strike or a consecutive toe off;
• calculate, based on the trajectory of the foot in the traveling direction at the detected gait events, a stride length corresponding to a movement distance of the foot in the traveling direction between the consecutive gait events;
• calculate, based on the plantar angle of the foot and a position of the inertial sensor at a timing of the heel strike and on a constraint condition that a lower leg of the user is substantially perpendicular to a ground at the timing of the heel strike, a distance between the inertial sensor and an ankle joint of the user;
• calculate, based on the stride length, the distance between the inertial sensor and the ankle joint, and on a geometric model on which constraint conditions related to motion of lower limbs of the user are imposed, a length of at least one segment of the lower limbs including at least one of a length of a lower leg between the ankle joint and a knee joint and a length of an upper leg between the knee joint and a hip joint;
• and
• output body dimension information including the calculated length of the segment of the lower limbs for use in control of a measurement or training support related to gait of the user.