Comparison Of Lower Limb Joint Angle During Gait Between Inertial Sensor And High-speed Infrared Motion Capture System

Research Purpose: With the development of miniaturization technology of inertial sensor,it can be used to measure the angle of human joints during movement.Compared with the traditional infrared motion capture system,it has the advantages of simple operation,convenient to carry,cheap price and can be used outdoors.As a new tool,its effect of measuring the angle of human joints can be tested by being compared with the infrared motion capture system.This study tests whether the measured value of gait lower limb joint angle of both inertial sensor and infrared motion capture system can be compared transversely and compares the repeatability of both the two motion capture system.Research Method: Two sessions of gait tests were performed on 20 subjects,5 times for each session,and a complete left leg gait cycle was collected each time.Gait data must be collected synchronously using both the inertial sensor and the infrared motion capture system.After the end of the first session,the infrared reflectance signs and inertial sensors on the subject's body surface should be removed,and then the reflectance signs and sensors are re-pasted,and at last the second test was conducted.By calculating the Coefficient of Multiple Correlation(CMC)and the System-Error,the transverse comparison of the measured values of the two motion capture systems was evaluated.The repeatability within session of the two motion capture systems was evaluated by calculating the Coefficient of Multiple Correlation within session,the Withinsession-Error.The repeatability between sessions of the two motion capture systems was evaluated by calculating the Coefficient of Multiple Correlation between sessions,the Betweensessions-Error.Research Result: The lower limb joint angle of the sagittal plane of the two systems can be compared transversely(CMC >0.86),while the one of the frontal plane and the horizontal plane cannot be compared transversely(0.28<CMC<0.72).The change trend of the joint angle of the sagittal plane and the abduction-adduction-axis of the hip joint can be compared transversely(CMC >0.89),while the change trend of the other lower limb joint angles cannot be compared transversely(0.51<CMC<0.74).The repeatability within session of inertial sensor is very high for the sagittal joint angle(CMC >0.97),not high for the hip joint rotation-axis angle(CMC<0.70),and high for the other lower limb joint angle(0.75<CMC<0.91).There is no significant difference of the repeatability within session for the sagittal plane between the inertial sensor ang the infrared motion capture system(p=0.104~0.416),but the repeatability within session for the other planes of the inertial sensors is significantly lower than the one of the infrared motion capture system(p=0.000~0.002).The inertial sensor has very high repeatability between sessions for sagittal joint angle(CMC>0.96),high repeatability between sessions for frontal joint angle(0.77<CMC<0.85),and low repeatability between sessions for horizontal joint angle(CMC<0.66).The repeatability between sessions of the hip-rotation joint angle of the inertial sensor is significantly lower than the one of the infrared motion capture system(p= 0.013),but there was no significant difference of the repeatability between sesseions of the other lower limb joint angles between the two motion capture systems(p=0.059~0.801).Research Conclusion: The measured values of the sagittal plane joint angle between the two motion capture systems can be compared transversely and the effect of the comparison of the change trend of the joint angle is better.The repeatability within sesseion of the inertial sensor is high,but still lower slightly than the one of the infrared motion capture system.The repeatability between sessions of inertial sensor for sagittal and frontal joint angle of lower limb is high,and the one for horizontal joint angle is not high.In general,there is no significant difference of the repeatability between sesseions between the inertial sensor and the infrared motion capture system.