Work-related distal upper limb musculoskeletal disorders are costly conditions that many
companies and researchers spend significant resources on preventing. Ergonomic assessments
evaluate the risk of developing a work-related musculoskeletal disorder (WMSD) by quantifying
variables such as the force, repetition, and posture (among others) that the task requires. Accurate
and objective measurements of force and posture are challenging due to equipment and location
constraints. Wearable sensors like the Delsys Trigno Quattro combine inertial measurement units
(IMUs) and surface electromyography to solve collection difficulties. The purpose of this work
was to evaluate the joint angle estimation of IMUs and the relationship between sEMG and overall
task intensity throughout a controlled wrist motion. Using a 3 degrees-of-freedom wrist
manipulandum, the feasibility of a small, lightweight wearable was evaluated to collect accurate
wrist flexion and extension angles and to use sEMG to quantify task intensity. The task was a
repeated 95º arc in flexion/ extension with six combinations of wrist torques and grip requirements.
The mean wrist angle difference (throughout the range of motion) between the WristBot and the
IMU of 1.70° was not significant (p= 0.057); but significant differences existed throughout the
range of motion. The largest difference between the IMU and the WristBot was 10.7° at 40°
extension; this discrepancy is smaller than typical visual inspection joint angle estimate errors by
ergonomists of 15.6°. All sEMG metrics (flexor muscle root mean square (RMS), extensor muscle
RMS, mean RMS, integrated sEMG (iEMG), physiological cross-sectional area weighted RMS)
and ratings of perceived exertion (RPE) had significant regression results with the task intensity.
Variance in RPE was better explained by task intensity than the best sEMG metric (iEMG) with
R2 values of 0.35 and 0.21, respectively. Wearable sensors can be used in occupational settings to
increase the accuracy of postural assessments; additional research is required on relationships
between sEMG and task intensity to be used effectively in ergonomics. There is potential for
sEMG to be a powerful tool; however, the dynamic nature and combined exertion (grip and
flexion/ extension) make it difficult to quantify task intensit
