Evaluation of wearable IMU performance for orientation estimation and motion tracking

Introducing objective wearable IMU measurements of functional movement quality into clinical assessments may improve accuracy of diagnosis. The goal of the present study was to assess the performance of inexpensive wearable IMUs relative to conventional motion capture equipment during controlled movements that are representative of typical human movement. Thirty-five cycles of spine flexion-extension, lateral bending, and axial twisting were simulated by means of a motorized gimbal at speeds of 20 cycles/min and 40 cycles/min. Differences between cycle-to-cycle maximum angle, minimum angle, and ROM values, as well as correlational analyses within IMUs and between IMUs and motion capture, in all movement directions, were compared. All absolute differences in measurements were 0.99) in all movement directions showing reliability between sensors and measurements. Overall, it was revealed that the sensors perform very well in the primary movement direction and one secondary axis; however, correlation in the third axis is suboptimal for orientation estimation and motion tracking

A subject-specific approach to detect fatigue-related changes in spine motion using wearable sensors

An objective method to detect muscle fatigue-related kinematic changes may reduce workplace injuries. However, heterogeneous responses to muscle fatigue suggest that subject-specific analyses are necessary. The objectives of this study were to: (1) determine if wearable inertial measurement units (IMUs) could be used in conjunction with a spine motion composite index (SMCI) to quantify subject-specific changes in spine kinematics during a repetitive spine flexion-extension (FE) task; and (2) determine if the SMCI was correlated with measures of global trunk muscle fatigue. Spine kinematics were measured using wearable IMUs in 10 healthy adults during a baseline set followed by 10 sets of 50 spine FE repetitions. After each set, two fatigue measures were collected: perceived level of fatigue using a visual analogue scale (VAS), and maximal lift strength. SMCIs incorporating 10 kinematic variables from 2 IMUs (pelvis and T8 vertebrae) were calculated and used to quantify subject-specific changes in movement. A main effect of set was observed (F (1.7, 15.32) = 10.42, p = 0.002), where the SMCI became significantly greater than set 1 starting at set 4. Significant correlations were observed between the SMCI and both fatigue VAS and maximal lift strength at the individual and study level. These findings support the use of wearable IMUs to detect subject-specific changes in spine motion associated with muscle fatigue