Table 2 Effects of stimulation signal parameters on muscle contractile responses

Study 1: analysis of the effect of changes in the duration of stimulation pulses on contractile measures

[29]

MMG: laser sensor (model LG10A65PU: Banner Engineering, Minneapolis, MN, USA; Class 2, sensing beam with a 670-nm visible red laser, power output = 0.20 mW, beam size = 0.06 × 0.8 mm, resolution = 10 μm)

BB

10 healthy male subject, age 19–33 years

Stimulation pulses were increased from 50 to 500 \(\mu s\) until no further increase in the MMG Dm was detected

The duration of the pulse impacted the muscle contractions reflected by MMG

Remark: the lateral displacement and rate of muscle contraction decreased from 50 to 300 µs, and none of the fibers were maximally activated below 300 µs

Future work: other muscles and the effect of skin impedance on other moderators must be evaluated in the future

Study 2: effect of non-isometric muscle activation on joint parameters and MMG

[30]

MMG: 9-mm² accelerometer (thickness = 4.5 mm, mass = 0.75 g, sensitivity = 500 mV/g where g = 9.8 m/s²; MP110-10-101, MediSens INS, Japan)

TA

8 healthy male subjects, age (means ± SDs) 27 ± 2.9 years, height 173 ± 9.1 cm, weight 73 ± 5.5 kg

The ankle joint and MMG were measured after one, two, three, four, seven and eight stimulation pulses separated by a 1–5-min rest; the 10-ms (100-Hz) pulses were administered at an inter-pulse interval of 10, 20, 30, 40, 50, 80 and 100 ms

At different inter-pulse intervals or numbers of stimuli, the MMG exhibited a poor correlation with the changes in joint kinematics

Remark: torque changes should not be considered for the control of the initial joint movement using functional electrical stimulation

Study 3: analysis of the effect of the inter-pulse duration on muscle contractile parameters

[31]

ES: stimulating electrodes (Compex Medical AS, Ecublens, Switzerland); TMG: (BMC Ltd., Ljubljana, Slovenia)

BB

13 male and 2 female subjects, age 29.5 ± 7.4 years, height 176.9 ± 9.2 cm, body mass 78.7 ± 14.9 kg

A 10-s ES was delivered to the BB positioned at 10, 45, 90° with the arm at rest for 10–20 s on 2 separate days. The delay time (Td), contraction time (Tc), sustained time (Ts), relaxation time (Tr) and maximal displacement (Dm) were compared between the 2 days

The test–retest reliability of TMG parameters was significant for 2 days

Remark: the interpretation of muscle contraction in terms of modeled muscle shapes depends on twitch contraction

Future work: the possible maximal stimulation response should be verified

Study 4: analysis of the effect of submaximal contraction on the MMG response

[32]

Accelerometer (13 × 18 mm, 0.94 g; MMA7260Q, Free scale)

RF

13 healthy male, age 21.3 ± 6.5 years, mass 79.3 ± 6.08 kg, height 179 ± 10.71 cm

The femoral nerve was excited by nine NMES frequencies at 1 kHz modulated at 20, 25, 30, 35, 40, 45. 50, 75 and 100 Hz

The relationship between NMES frequencies and MMG responses is not linear

Remark: a high frequency does not impact the mechanomyographic characteristics and thus does not affect for the application of a neuroprosthetic device

Study 5: analysis of the effect of post-activation potentiation on the MMG of synergistic muscles

[33]

EMG: 11-mm pick-up diameter, 25 mm inter-electrode distance; MMG: uniaxial accelerometer (dimensions = 9 × 9 × 5 mm, mass = 0.75 g, model MP101-10, MediSens, Japan)

MG and SOL

8 male subjects, age (means ± SDs) 26.86 ± 3.7 years, height 176.1 ± 6 6.3 cm, mass 71.2 ± 6 6.1 kg

Before and after a 10-s MVC, a 500-µs pulse was delivered every 1 min for 5 min, and one stimulus was applied after 10 min. The evoked MMG was measured before and after 10-s supramaximal plantar flexion

The potentiation of both muscles with the plantar flexion angle was investigated. The MG showed a higher MMG amplitude than SOL at DF and NP

Remark: a 10-s dorsiflexion and neutral position of the MG showed greater potentiation than SOL, but no significant difference in PAP for plantar flexion was found between the two conditions

Study 6: analysis of the effect of post-activation potentiation on MMG

[34]

MMG: (MP110-10-101, MediSens, Inc., Japan; sensitivity = 500 mV/g, where g = 9.8 m/s²)

MG

10 healthy male subjects, age 25.8 years, height 170.3 ± 4.8 cm, weight 67.8 ± 7.5 kg

After supramaximal stimulation to determine the M-wave and a 10-min rest, three isometric contraction at a 5-s interval were delivered for each twitch stimuli. Twitch contractions were evoked 2, 15, 30, 60 and 180 s after the MVC

No change in the M-wave was found after MVC. MMG measured after the evoked twitch contractions reflect changes in muscle contraction

Remark: after PAP, the evoked MMG-PP represents the contractile properties of the muscle

Study 7: analysis of the intensity and contraction velocities of skeletal muscles

[37]

MMG: accelerometer (ADXL330, Analogue Devices, Inc., Norwood, MA, USA); EMG: Ag–AgCl electrodes (EL503; Biopac Systems Inc.)

Soleus muscle

3 male and 5 female subjects, age 19 ± 1 years

An H-M recruitment curve was mapped for the soleus muscle by increasing the 0.1-ms square wave at 1.0- to 5-V increments with a 10-s rest interval until an M-wave was recruited

The maximum sEMG corresponding to H-reflex and M-waves showed a moderate correlation between HM and \({MMG}_{PP}\)

Remark: the time-to-maximum intensity (TTMax) was longer at a low stimulation intensity and declined with increases in the intensity

Future work: further studies should account for the body composition, muscle fiber composition, gender and training

Study 8: effect of unilateral surface stimulation session on the contralateral limb

[35]

MMG: 6.5-g accelerometer (K-Beam 8305A; Kistler, Amherst, MA, USA); EMG: Ag/AgCl bipolar surface electrodes (Blue Sensor M-00-S; Medicotest, Ølstykke, Denmark)

RF

36 healthy right-footed male subjects, age 25.8 ± 1.3 years, weight 75.0 ± 2.1 kg, height 178.3 ± 1.1 cm

After stimulation at 100 Hz with a 300-µs pulse duration, a cycle of 10 s on and 10 s off was applied for relaxation of the RF of the non-dominant leg of the 18 RS group for 10 min

MMG, EMG and maximum voluntary isometric contraction from the dominant leg before and after stimulation showed no changes in the MMG activity of the RF (p < 0.05)

Remark: the lack of mechanical changes could be due to the short exposure time to the stimulus

Future work: the influence of a long exposure time to the stimulus on the tension, rigidity, mass and length of the muscle should be investigated

Study 9: analysis of the effect of the staircase phenomenon on neuromuscular blockade (NMB) monitoring

[36]

AMMG (train of four (TOF)–Watch SX; Organon, Dublin, Ireland)

Abductor pollicis

17 males and 7 females in group C, age 45.9 years, BMI 25.6 kg/m²; 17 males and 5 females in group S, age 47.9 years, BMI 25.1 kg/m²

Group C received 2-Hz TOF every 15 s over 20 min, and rocuronium was injected into the other hand Group S was tetanically stimulated (50 Hz, 5 s, and 50 mA)

Prior to acceleromyography, tetanic stimulation resulted into reduced onset and recovery times of AMMD amplitudes

Remark: sp has no influence on the TOF ratio

Future work: the effect of sensitivity on monitoring NMB function should be investigated