Table 3 Overview of the use of ES and MMG in sensor validation
From: Assessment of muscle activity using electrical stimulation and mechanomyography: a systematic review
| Study 1: validation of Ag–PDMS substrate for the electrostimulation of muscles | |||||
|---|---|---|---|---|---|
| Authors | Sensor and electrode type | Electrode site | Dataset | Methodology | Results and discussion |
| [38] | Ag–PDMS composite | BB | Not reported | Single and array electrodes composed of Ag/Ag–PDMS and PDMS/OHP substrates were used, and MMG signals were recorded for testing purposes | The responses were similar to those obtained with a single commercial electrode, with an average peak of 7000–10,000 mV |
| Remark: the Ag–PDMS can be bent and stretched, which was a limitation of the Ag–OHP paper electrode | |||||
| Study 2: evaluation of a lever indentor and a moving magnet galvanometer for MMG recording | |||||
| [39] | ES: galvanically isolated stimulator (MYOSTIM); MMG: scanner galvanometer; Force: ankle dynamometer (RAFOLT and GALLASCH, 1996) | Calf muscles | 6 healthy subjects | 9 stimulation pulses were delivered to achieve a contraction of 70 N, whereas the indentor was adjusted to 0.1, 0.5 and 5 N. Under isometric contraction of the calf muscles, an ankle dynamometer was used to record the surface response from the gastrocnemius muscle | The amplitudes of MMG-RMS showed direct increases during contraction |
| Remark: a unity cross-correlation coefficient confirmed the validity of using a galvanometer for recording MMG signals | |||||
| Future work: further studies should verify indirect stimulation | |||||
| Study 3: analysis of the accuracy of an accelerometer for tensiomyography | |||||
| [40] | TMG: optical encoder (4 µm, 0.25 mm−1; a spherical tip of 12 mm−2); MMG: displacement accelerometer | BB | Not reported | A single-twitch stimulus consisting of a 1-ms, 20-mA square pulse was delivered to the BB using two self-adhesive electrodes. The double integration of the acceleration records were compared with the optical encoder records | The MEM accelerometer efficiently detects short-term small muscle displacement |
| Remark: the difference in \({D}_{m}\) recorded from an accelerometer and a displacement sensor and the time parameter must not differ by more than 0.05 mm and 0.5 ms, respectively | |||||
| Study 4: characterization of muscles and subcutaneous tissues | |||||
| [41] | ES: Ag–AgCl; DMMG: (LK-G80, Keyence, Osaka); AMM: (MP-110-10-101, MediSens, Saitama) | TA | 6 healthy males, age 22–25 years | A monopolar rectangle pulse with a 500 µs in width and an inter-pulse interval of 600 ms was applied | Good identification of the longitudinal and transversal mechanics of the muscle, subcutaneous tissue and skin was achieved |
| Remark: the natural frequency of an acceleration sensor fluctuates more than that of a displacement sensor, but the latter is limited to longitudinal muscle mechanics | |||||
| Future work: the effect of the mass of subcutaneous tissue on the natural frequency should be investigated | |||||
| Study 5: analysis of the reliability of MMG and a laser-displacement sensor | |||||
| [42] | MMG: laser-displacement sensor (LDS; class 2 laser; model LG10A65PU, Banner Engineering Australia) and contact-displacement sensor (CDS; Positek P101 Stand Alone Linear Position Sensor) | RF | 16 female and 14 male subjects, age (means ± SDs) 22 ± 2.7 years, height 1.70 ± 0.09 m, body mass 68.9 ± 11.0 kg | Stimulation with a voltage of 400 V, a pulse duration of 200 µs, and a current amplitude of 40—280 mA with 10-mA increments was applied until the muscle reached full displacement; five successive single twitches were delivered at maximum intensity | Both sensors showed good test–retest reliability over the four testing sessions |
| Remark: the two sensors are not interchangeable: the CDS appears to be more sensitive to muscle belly displacement, whereas the LDS shows increased sensitivity | |||||
| Future work: the allocation between the stimulation interval and ½ Tr should be well monitored in order to ensure an efficient recovery time for all MMG parameters | |||||
| Study 6: evaluation of MC sensors | |||||
| [43] | ES: 5–9 cm (RehaTrode, Hasomed GmbH, Magdeburg, Germany); MMG: (TMG-BMC Ltd., Ljubljana, Slovenia) | RF | 9 SCI subjects, age 41.6 ± 14.5 years | A stimulation with 35 Hz, 200 µs and an amplitude of 70—110 mA was followed by MC recording to predict the torque | The MC sensor torque and the dynamometer knee torque were linearly correlated |
| Remark: MC sensor measurements are reliable and can be used as an alternative for fatigue estimation | |||||
| Future work: an experiment using a high number of subjects with SCI and different protocols should be performed to validate the use of an MC sensor for real-time data transmission | |||||
