Table 1.

Details of records on torque assessment.

Authors	Sensor used	Subjects	Muscle activity assessed	Experimental protocol	Parameters	Results	Application / Limitation / Future work
21	Piezoelectric crystal sensor	10 (6 men, 4 women)	Effect of dehydration on muscle torque	Sub maximal isometric contractions at 25%, 50%, and 75% MVC	Torque, MMG MPF and MMG RMS	No change in the torque, RMS and MPF (both EMG & MMG) values after dehydration.	Effect of dehydration can be studied on other muscles using MMG in future.
22	Piezoelectric crystal sensor	18 (10 men, 8 women)	Ability of muscle to produce torque after static stretching	Maximal dynamic torque production	Torque, EMG and MMG amplitudes	Torque increases while moving from stretching to non-stretching protocol.	Effect of change in muscle temperature and blood flow on muscle stiffness was not considered.
23	Piezoelectric crystal contact sensor	12 (6 men, 6 women)	Modulation in dynamic torque production due to isokinetic muscle action	Submaximal to maximal isokinetic actions	Torque, MMG amplitude and MPF, EMG amplitude and MPF	The MMG and EMG RMS show a linear relation with increasing peak torque	The study could be extended in future to other body muscles taking MMG signal contamination into account.
11	Piezoelectric crystal sensor	10 (5 men, 5 women)	Torque assessment during isokinetic and isometric contraction	Isometric and isokinetic testing at 10% to 90% MVC	MMG amplitude, MMG MPF and torque	MMG amplitude increases in isokinetic testing while MMG amplitude flattens and MPF decreases in isometric testing from 80% to 100% MVC.	MMG amplitude and frequency response in relation to torque can be observed for other muscles in future.
26	Piezoelectric crystal sensor	8 (6 men, 2 women)	Eccentric torque production	Submaximal to maximal eccentric isokinetic muscle actions	MMG MPF, MDF, peak torque	MMG CF obtained for the biceps brachii muscle increases linearly with increases in eccentric isokinetic torque from 10% to 100% peak torque.	Fourier based time-frequency methods can be used in future to process MMG signal coming from other muscles as well.
29	Piezoelectric contact and accelerometer	10 (5 men, 5 women)	Torque response under isokinetic and isometric forearm flexion	Submaximal to maximal isokinetic and isometric muscle actions	Torque, MMG amplitude for both the contact sensors and accelerometer, MMG MPF	The contact sensor and accelerometer resulted in different torque-related responses that might affect the interpretation of the motor control strategies involved.	MMG amplitude and frequency response may be compared in both contact sensor and accelerometer for muscle under fatiguing contraction.
27	Accelerometer	10 men	Estimation of torque through MMG	Transcutaneous muscle electrical stimulation	Peak torque and MMG peak to peak amplitude	A strong correlation between peak torque and MMG peak to peak amplitude in fatigue was found.	Specialized dynamometer was not used to measure joint torque accurately instead of load cell.
28	Displacement sensor	15 men	Torque and muscle deformations	Isometric twitch response	Delay time, Tc, half-relaxation time, Dm	Parabolic relation between transversal displacement and torque amplitude was observed.	Contractile properties have been assessed for transversal and longitudinal biceps brachii response only. Lateral response in terms of contractile properties may also be measured for same methodology in future, so that a good comparison can be made among three axis responses.
24	Accelerometer	10 (4 men, 6 women)	Maximal non-fatigue torque level derived from MMG, EMG and critical torque	Isometric contractions at 30, 45, 60 and 75% MVIC	Critical torque, mechanomyographic fatigue threshold from frequency content, electromyographic fatigue threshold from frequency content	No differences in the isometric torque levels associated with Critical torque, mechanomyographic fatigue threshold from frequency content and electromyographic fatigue threshold from frequency content were observed.	Fatigue threshold tests can be validated by dynamic muscle actions in future.
25	Accelerometer	7 men	Torque estimation via the MMG signal	Incremental / dynamic voluntary contractions	Muscle torque, MMG RMS, MMG MPF	The estimation obtained using the MMG torque estimator was more accurate than linear mapping.	Number of subjects considered for torque estimation experiment is very small.