The Effect of Sensor Placement on Measured Distal Tibial Accelerations During Running

Abstract

Inertial measurement units (IMUs) attached to the distal tibia are a validated method of measuring lower-extremity impact accelerations, called tibial accelerations (TAs), in runners. However, no studies have investigated the effects of small errors in IMU placement, which would be expected in real-world, autonomous use of IMUs. The purpose of this study was to evaluate the effect of a small proximal shift in IMU location on mean TAs and relationships between TAs and ground reaction force loading rates. IMUs were strapped to 18 injury-free runners at a specified standard location (∼1 cm proximal to medial malleolus) and 2 cm proximal to the standard location. TAs and ground reaction forces were measured while participants ran at self-selected and 10% slower/faster speeds. Mean TA was lower at the standard versus proximal IMU location in the faster running condition (P = .026), but similar in the slower (P = .643) and self-selected conditions (P = .654). Mean TAs measured at the standard IMU explained more variation in ground reaction force loading rates (r2 = .79−.90; P < .001) compared with those measured at the proximal IMU (r2 = .65−.72; P < .001). These results suggest that careful attention should be given to IMU placement when measuring TAs during running.

A 0.05 m Change in Inertial Measurement Unit Placement Alters Time and Frequency Domain Metrics during Running

“…Overall, the differences observed both here and in previous work [34,37,38] underscore the importance of placing IMUs correctly and preventing their movement throughout data collection. Ruder et al [35] previously demonstrated that IMUs placed by untrained participants have lower validity and inter-session reliability than IMUs placed by trained experimenters.…”

“…Although we are not aware of any previous investigations of IMU misplacement at the pelvis or sacrum during running, Sara et al [ 37 ] and Zhang et al [ 38 ] have previously reported the effects of IMU misplacement on proximal–distal (y axis) acceleration magnitudes at the shank. Sara et al placed a reference IMU on the medial malleolus and ‘misplaced’ another IMU 0.02 m proximal.…”

“…Unfortunately, the critical effects of IMU misplacement and movement on running data are little explored. Previous research suggests that small variations in IMU location can affect estimated ground reaction forces, knee joint angles, and inter-session reliability in walking [ 34 , 35 , 36 ], shank and foot accelerations in running [ 37 , 38 , 39 ], and lumbar accelerations in cadavers [ 40 ]. However, systematic quantification of the effects of placement variation on acceleration and angular velocity time and frequency domain metrics in vivo is still lacking.…”