Table 1 Effects of electrode repositioning on the reliability of muscle contractions

Study 1: analysis of the effect of the skinfold thickness on the MMG responses in voluntary and stimulated muscles

[25]

MMG: active miniature accelerometer (EGAS-FS-10-/V05, Measurement Specialties, Inc., Hampton, VA, USA); force: load cell (LC402, Omegadyne, Inc., Sunbury, OH, USA)

VL and RF

17 healthy male subjects, age 21 ± 2 years, weight 81.9 ± 13.6 kg, height 1.8 ± 0.09 m; and 23 healthy female subjects, age 21 ± 2 years, weight 67.3 ± 8.9 kg, height 1.69 ± 0.07 m)

The stimulation site was determined after M-wave detected with 20 mA. The stimulation increased from 2 to 100 mA. The skinfold thickness was obtained using MMG and EMG electrodes sites and averaged to represent the thickness of each subject. MMG GLM and EMG M-waves, in terms of the log-transformation of EMG-RMS and MMG-RMS-force relationship, were correlated with the skinfold thickness

The terms and skinfold thickness were not significantly correlated, and a non-meaningful correlation was found among the skinfold thickness, EMG M-waves and MMG GLM

Remark: a significant relationship was found between the MMG GLM and the skinfold thickness of the VL and RF under non-voluntary contraction

Future works:

1. The influence of subcutaneous fat on MMG and EMG signals and the spectral characteristics of the test variables should be investigated

2. The possible geometrical alteration of subcutaneous tissues and spectral features of EMG, MMG, and force during isometric contractions should be investigated

Study 2: analysis of the reliability and effect of the inter-electrode distance on TMG parameters

[26]

ES: self-adhesive electrodes (Compex Medical SA, Ecublens, Switzerland); TMG: (GK 40, Panoptik d.o.o., Ljubljana, Slovenia)

Right and left of the VM

18 healthy male subjects, age 22.9 ± 3.8 years, height 171 ± 10 cm, body mass 66 ± 10 kg

A current with 1-ms pulse duration and increases from 50 to 11 mA at 10-mA intervals was applied until no increase in the Dm was observed. Rater A positioned the sensors at ± 5 cm, marked ± 3 cm IED and left the room after removing electrode. Similarly, rater B performed test 2. Rater A then performed tests 3 and 4 with placements at ± 5 and ± 3 cm

Due to electrode repositioning, a decrease in the IED from ± 5 to ± 3 cm lowered the Dm (p < 0.01). Thus, the IED should be maintained during experiments requiring electrode repositioning

Remark: all contractile parameters showed good inter-rate reliability with the exception of Tr with an ICC of 0.99

Future work: an experimental confirmation of TMG parameters should be conducted with different subjects, muscles groups and side-to-side asymmetry

Study 3: analysis of the inter-changeability of TMG and ultrasound

[27]

TMG: (TMG-BMC Ltd., Ljubljana, Slovenia)

BF, VMO and VML

10 male subjects, age 24.3 ± 2.6 years

Innervation points were detected using tetanic stimulation (0.1 ms and 10 Hz). TMG parameters were extracted after stimulation with 110 mA at 30 V. The Tc, Dm, and velocity of the radial displacement (Vr) were measured after an ultrasound B-mode scan of the same location

The contractile parameters measured with TMG and the structural parameters measured with ultrasonography were positively correlated

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

Future work: the assessment of muscle contractile functions in terms of angle and inter excitation interval should be investigated

Study 4: analysis of the structure and function of VMO and VML using TMG

[28]

ES: self-adhesive anode and cathode (Axelgaard Manufacturing); TMG: (TMG-BMC, Ljubljana, Slovenia)

VML and VMO

mATPase histochemistry: 9 male subjects who experienced sudden death, age 18–44 years; TMG: 15 healthy sedentary male subjects, age 20–37 years

VML and VMO blocks frozen in nitrogen at – 196 °C, were cut into cryostat at − 20 °C for myofibrillar adenosine triphosphate activity. The muscles fibers were classified into types 1, 3a, 2b, and 2c at different pH levels TMG experiment VML and VMO received 1-kHz, monophasic pulse at 1 ms to induce Dm and three 10-s twitches followed

The TMG signal responses of electrical stimulation from two different regions has shown significant difference in \({T}_{C}\),\({D}_{m}\), and \({T}_{r}\) and a constant \({T}_{d}\)

Remark: the anatomical and histochemical behaviors of VMO and VML are similar, but their biological functions are different

Future work: the determination of the biochemical function during voluntary contraction should be further considered