Transcutaneous neuromuscular electrical stimulation: influence of electrode positioning and stimulus amplitude settings on muscle response

Abstract

The aim of the study was to investigate the influence of two different transcutaneous neuromuscular electrical stimulation procedures on evoked muscle torque and local tissue oxygenation. In the first one (MP mode), the cathode was facing the muscle main motor point and stimulus amplitude was set to the level eliciting the maximal myoelectrical activation according to the amplitude of the evoked electromyogram (EMG); in the second one (RC mode), the electrodes were positioned following common reference charts for electrode placement while stimulus amplitude was set according to subject tolerance. Tibialis Anterior (TA) and Vastus Lateralis (VL) muscles of 10 subjects (28.4 ± 8.2 years) were tested in specific dynamometers to measure the evoked isometric torque. The EMG and near-infrared spectroscopy probes were placed on muscle belly to detect the electrical activity and local metabolic modifications of the stimulated muscle, respectively. The stimulation protocol consisted of a gradually increasing frequency ramp from 2 to 50 Hz in 7.5 s. Compared to RC mode, in MP mode the contractile parameters (peak twitch, tetanic torque, area under the torque build-up) and the metabolic solicitation (oxygen consumption and hyperemia due to metabolites accumulation) resulted significantly higher for both TA and VL muscles. MP mode resulted also to be more comfortable for the subjects. Based on the assumption that proper mechanical and metabolic stimuli are necessary to induce muscle strengthening, our results witness the importance of an optimized, i.e., comfortable and effective, stimulation to promote the aforementioned muscle adaptive modifications.

Electrical stimulation for neuromuscular testing and training: state-of-the art and unresolved issues

“…Motor point stimulation as a sine qua non-condition to optimize NMES use Gobbo et al (2011) provided convincing evidence on the importance of motor point determination to minimize current intensity and discomfort, and to maximize the muscular tension evoked by NMES. They also used near infrared spectroscopy, which is a technique particularly suitable for investigating local metabolic changes of stimulated muscles (Muthalib et al 2009), and were able to demonstrate that, besides contractile activity, muscle oxygen consumption and hyperaemia were significantly increased when motor point location was carefully determined with a pen electrode rather than being inferred from several legally marketed motor point charts.…”

“…They also used near infrared spectroscopy, which is a technique particularly suitable for investigating local metabolic changes of stimulated muscles (Muthalib et al 2009), and were able to demonstrate that, besides contractile activity, muscle oxygen consumption and hyperaemia were significantly increased when motor point location was carefully determined with a pen electrode rather than being inferred from several legally marketed motor point charts. We recommend that the procedure described by Gobbo et al (2011), which is completed in less than a minute, should be consistently incorporated in both clinical and research contexts to optimize NMES application. Botter et al (2011) investigated the uniformity of the muscle motor point location in the lower limb of healthy subjects and found different motor points innervating different portions of the quadriceps, posterior thigh, and tibialis anterior muscles.…”

“…In order to maximize the spatial recruitment during NMES, thus minimizing the extent of muscle fatigue, it has been recommended to implement different expedients during a treatment session such as progressive increase in current intensity, alteration in muscle length, and displacement of active electrodes (Maffiuletti 2010). In this cluster of articles, further approaches have been proposed to alleviate, at least in part, discomfort and other possible complications associated to the electrically evoked contractions (Botter et al 2011;Bergquist et al 2011;Gobbo et al 2011). Fig.…”

Reliability of the Electromechanical Delay Components Assessment during the Relaxation Phase

“…St-Pro Multichannel Programmable Neuromuscular Stimulator, LiSin, Turin, Italy). The stimulation return electrode (anode: 130 × 100 mm) was positioned at the third distal of the leg, whereas the stimulation electrode (cathode: 90 × 40 mm) was placed over the most proximal motor point of the GM muscle [20]. A set of brief 2 Hz stimulations of increasing amplitude was administered to determine the maximum compound motor unit stimulus (M-wave).…”

The Effect of Burst-Duty-Cycle Parameters of Medium-Frequency Alternating Current on Maximum Electrically Induced Torque of the Quadriceps Femoris, Discomfort, and Tolerated Current Amplitude in Professional Soccer Players

“…Several authors have demonstrated the influence of stimulation parameters, such as electrode positioning, 20 current frequency, 38,44,[53][54][55] current amplitude (intensity), 8,22,44 stimulus pulse duration, 22,23 and burst duty cycle of medium-frequency alternating current, 33,37,55 on electrically induced torque. Burst duty cycle is an important parameter of NMES, as it can directly affect torque production and sensory discomfort in healthy, untrained individuals.…”