Mechanomyographic analysis for muscle activity assessment
during a load-lifting task

The purpose of this study was to compare Electromyographic (EMG) with Mechanomyo- 1
 graphic (MMG) recordings during isometric conditions, and during a simulated load-lifting task. 2
 Twenty-two males (age: 25.5 ± 5.3 years) first performed maximal voluntary contractions (MVC) and 3
 submaximal isometric contractions of upper limb muscles at 25%, 50% and 75% MVC. Participants 4
 then executed repetitions of a functional activity simulating a load-lifting task above shoulder level, 5
 at 25%, 50% and 75% of their maximum activity (based on MVC). The low frequency part of the 6
 accelerometer signal (< 5 Hz) was used to segment the 6 phases of the motion. EMG and MMG were 7
 both recorded during the entire experimental procedure. Root mean square (RMS) and mean power 8
 frequency (MPF) were selected as signal extraction features. During isometric contractions, EMG 9
 and MMG exhibited similar repeatability scores. They also shared similar RMS vs force relationship, 10
 with RMS increasing to 75% MVC and plateaued to 100%. MPF decreased with increasing force to 11
 75% MVC. In dynamic condition, RMSMMG exhibited higher sensitivity to changes in load than 12
 RMSEMG. These results confirm the feasibility of MMG measurements to be used during functional 13
 activities outside the laboratory. It opens new perspectives for future applications in sports science, 14
 ergonomics and human-machine interfaces conception.