Torque Amplitude Research Articles

Maximum power point tracking control of wind turbines based on speed hysteresis loop to reduce drive-train loads

By adding compensation torque based on the optimal torque, the torque compensation control method expands the unbalanced torque at varying wind speeds, thereby improving the maximum power point tracking (MPPT) performance of wind turbines (WT). However, while improving the wind energy capture efficiency, such methods will lead to drastic fluctuations of generator torque, resulting in significantly increased drive-train loads. To solve this problem, based on the amplitude-frequency characteristics analysis of the WT system transfer function, it is found rotor speed information can not only reflect the main trend of wind speed changes, but also has the characteristics of not being easily affected by the high-frequency component of wind speed. Therefore, setting compensation torque according to it can effectively alleviate the above phenomenon. On this basis, the MPPT control of WT based on speed hysteresis loop to reduce drive-train loads is proposed. The speed information is used to replace the torque information to set the compensation torque amplitude term, and the speed hysteresis loop is introduced to improve the design of the compensation torque symbol term, which can significantly decreased drive-train loads without compromising on power capture. Finally, the effectiveness of the proposed method is verified by the experiments.

Multi-Objective Optimization Analysis of Electromagnetic Performance of Permanent Magnet Synchronous Motors Based on the PSO Algorithm

In order to optimize the electromagnetic performance of a permanent magnet synchronous motor (PMSM) during operation, this paper takes the size of the stator slot structure of the motor as the optimization variable and the peak cogging torque and no-load back electromotive force (EMF) amplitude of the motor as the optimization objectives. A multi-objective optimization method based on the particle swarm optimization (PSO) algorithm is adopted to obtain a structural parameter combination that minimizes the peak cogging torque and no-load back EMF amplitude while meeting the reasonable range requirements of magnetic flux density amplitude. The optimized motor structure design prototype is experimentally verified. The results show that through multi-objective optimization based on the PSO algorithm, the electromagnetic performance of the motor has been improved, with a reduction of 36.33% in peak cogging torque and 2.65% in peak no-load back EMF, indicating a reasonable magnetic flux density amplitude. The experimental results of the optimized prototype show that the difference between the theoretical simulation values and the experimental values is within a reasonable range, which verifies the effectiveness of the multi-objective optimization method.

Nonlinear Dynamics Induced by Coil Heat in the PMDC Motor and Control

In this paper, the interesting dynamics of chaos induced by the effect of the variation of internal average heat during operation in the DC motor control by the full bridge drive are analyzed. By using simple powerful tools of analyzing nonlinear dynamical systems like phase portraits, time traces and frequency spectrum in the MATLAB-SIMULINK environment, we showed that under certain conditions, the PMDC motor develops different behaviors so as periodic limited, and chaotic attractors, when the motor drive different form of external load torque and the windings resistance variation. This paper presents the first studies on the variation of the average heat of the motor and the amplitude of the triangular load torque to produce the strange phenomena like chaos as far as our knowledge go. A chaos control of the unstable regime is proposed to stabilize the PM DC motor in a desire regime. This contribution is very important in industry because some unexplained dynamical behaviors of the DC motor driven by a full bridge now can be avoided.

Enhancement on PDC bit based on Archimedean spiral control method

The Longmaxi Formation shale in the Sichuan Basin has a large burial depth, narrow horizontal windows, and stringent requirements for controlling well deviations. When PDC bits are used for drilling, the cutting structure experiences significant challenges in terms of stability and rock-breaking efficiency. The secondary design cycle of PDC bits is lengthy, and the cost of engineering trials is high. Thus, bit development relies on strong empirical knowledge. Additionally, the spiral degree of the blades has not been uniformly defined, and there was a lack of quantitative studies about its effect on the rock-breaking performance of PDC bits. In this study, thus Archimedean spiral was used as the quantitative control equation for the spiral degree of the blades. The cutting depth control distance ΔL2 (or designed depth of cutting, designed DOC) and the level of different track (LODT) were used to adjust the radial cutting section of the interaction process between the bit and shale. An orthogonal coupling study was conducted on the rock-breaking efficiency and stability of 8 1/2ʺ PDC bits with six spiral span angles θspan, six cutting depth control distances ΔL2, and six LODTs as design parameters. The results indicated that using the triaxial compressive strength under the liquid column pressure as the mechanical specific energy (MSE) benchmark, the shear failure mode reduced the mechanical specific energy below this benchmark when cutting depth control distance ΔL2 of the front and rear elements exceeded 1.0 mm. However, increasing the cutting depth control distance ΔL2 led to an increase in torque and circumferential vibration amplitude. In addition, compared to straight blade designs, spiral blade designs significantly reduced the axial/circumferential vibrations, with reductions in circumferential vibration amplitude ranging from 37.87% to 48.33%. The spiral blade designs had a suppressive effect on axial vibrations only when the spiral span angle θspan was between 12 and 36° or 60°, reducing the axial vibration amplitude by approximately 20.09–25.69%. Different ΔL2 must be considered in conjunction with cutter material properties when selecting the spiral span angle based on the simulation results. When the ΔL2 exceeded 1.0 mm, LODT of 3/6 could maximize the reduction in the mechanical specific energy. Using MSE as the objective function, this study provided several PDC bit enhancement design schemes suitable for the Longmaxi Formation. The research results contributed to a quantitative understanding of the coupling effects between spiral span angle θspan and cutting sections on the rock-breaking efficiency and stability of PDC bits.

Evaluating resistance drilling and NIR spectroscopy for quantifying wood quality of young eucalypts grown in Guangxi province in southern China

Cost-effective, non-destructive means of estimating wood properties of eucalypts grown in Guangxi, China, were evaluated using near infrared (NIR) spectroscopy and resistance drilling. For this evaluation, wood samples for NIR analysis and resistance drill measurements were collected from 581 trees, representing eight plantation Eucalyptus taxa across five sites. The near infra-red (NIR) spectra collected from the 581 wood samples were analysed using existing calibrations for kraft pulp yield, cellulose content, hot water extractives and Klason lignin. These spectra and calibrations were effective in predicting over 60% of the variance in total carbohydrates and over 80% of the extractives and lignin values from independent laboratory analysis of a subset of 100 samples. Resistance drilling combined with software developed for processing the drill data proved to be a quick, low cost and effective means of quantifying wood density (as amplitude of the drill torque), stem diameter and bark thickness.

Reduction and recovery of self-sustained muscle activity after fatiguing plantar flexor contractions.

Persistent inward calcium and sodium currents (PICs) are crucial for initiation and maintenance of motoneuron firing, and thus muscular force. However, there is a lack of data describing the effects of fatiguing exercise on PIC activity in humans. We simultaneously applied tendon vibration and neuromuscular electrical stimulation (VibStim) before and after fatiguing exercise. VibStim induces self-sustained muscle activity that is proposed to result from PIC activation. Twelve men performed 5-s maximal isometric plantar flexor contractions (MVC) with 5-s rests until joint torque was reduced to 70%MVC. VibStim trials consisted of five 2-s trains of neuromuscular electrical stimulation (20 Hz, evoking 10% MVC) of triceps surae with simultaneous Achilles tendon vibration (115 Hz) without voluntary muscle activation. VibStim was applied before (PRE), immediately (POST), 5-min (POST-5), and 10-min (POST-10) after exercise completion. Sustained torque (Tsust) and soleus electromyogram amplitudes (EMG) measured 3 s after VibStim were reduced (Tsust: -59.0%, p<0.001; soleus EMG: -38.4%, p<0.001) but largely recovered by POST-5, and changes in MVC and Tsust were correlated across the four time points (r=0.69; p<0.001). After normalisation to values obtained at the end of the vibration phase to control for changes in fibre-specific force and EMG signal characteristics, decreases in Tsust (-42.9%) and soleus EMG (-22.6%) remained significant and were each correlated with loss and recovery of MVC (r=0.41 and 0.46, respectively). The parallel changes observed in evoked self-sustained muscle activity and force generation capacity provide motivation for future examinations on the potential influence of fatigue-induced PIC changes on motoneuron output.

Research on the dynamic performance of double-helical planetary gear transmission under friction and wear

In this paper, the main research is to investigate the effects of mechanical, friction, temperature, and tooth wear on the dynamic performance of a double-helical planetary gear transmission system. To achieve this, a new lumped parameters model is presented, which combines dynamics and lubrication. The model allows for the study of excitation effects and considers various parameters such as material, lubricating oil, and working conditions. By proposing a multi-source excitation calculation method, the paper provides a novel approach that has not been reported in the existing literature. Additionally, the paper establishes a tooth wear model and a lubrication model for the double-helical gear pair. It shows that under constant torque, the displacement and acceleration amplitudes of the system initially decrease and then increase with increasing input speed. Under constant speed, the displacement and acceleration amplitudes increase with increasing torque. Amplitudes decrease during running-in wear, increase in stable wear, and rapidly increase in severe wear. Boundary lubrication minimizes vibration, while elastohydrodynamic lubrication maximizes it.

Performance characterization and modeling of an oscillating surge wave energy converter

Testing wave energy converters in the ocean could be expensive and complex, which necessitates the use of numerical modeling. However, accurately modeling the response of wave energy converters with high-fidelity simulations can be computationally intensive in the design stage where different configurations must be considered. Reduced-order models based on simplified equations of motion can be very useful in the design, optimization, or control of wave energy converters. Given the complex dynamics of wave energy converters, accurate representation, and evaluation of relative contributions by different forces are required. This effort is concerned with a performance characterization of the hydrodynamic response of an oscillating surge wave energy converter that is based on a reduced-order model. A state-space model is used to represent the radiation damping term. Morison’s representation of unsteady forces is used to account for the nonlinear damping. Wave tank tests are performed to validate simulations. A free response simulation is used to determine the coefficients of the state-space model. Torque-forced simulations are used to identify the coefficients of the nonlinear damping term for different amplitudes and wave frequencies. The impact of varying these coefficients on the response is investigated. An assessment of the capability of the model in predicting the hydrodynamic response under irregular forcing is performed. The results show that the maximum error is 3% when compared with high-fidelity simulations. It is determined that the nonlinear damping is proportional to the torque amplitude and its effects are more pronounced as the amplitude of the flap oscillations increases.

On the origin of systematic errors in VSM torque curves

Magnetic anisotropy (MA) is a basic and crucial magnetic property which describes how the magnetic properties change with field angle in a magnetic composite. Torque measurements are normally used to measure a sample’s anisotropy constant and can be determined directly using a torque magnetometer (TM) or indirectly using a vibrating sample magnetometer (VSM). Most TM only operate at room temperature. However, a biaxial VSM allows straightforward torque measurements at varying temperatures. VSM torque curves comprise a 2θ background caused by small misalignments of the sample on the sample rod, and/or a non-azimuthal symmetric sample shape. These errors originate from the position dependence of the pickup coil sensitivity matrix. Here, the magnetic torque of a strontium ferrite/PA-12 3D printed samples was explored using biaxial VSM and compared to measurements done with a true torque magnetometer. Torque curves were taken from 16-22kOe every 2kOe on a 4.8 mm wire and a 1.23 mm dot sample using a MicroSense EZ9 VSM. Fourier analysis was used to determine the second harmonics from each torque curve. The biaxial torque curves of the wire samples have a much larger torque amplitude which is mainly due to the crosstalk of the y-coil set. Crosstalk originates from the non-azimuthal symmetric shape of the sample and due to the wobble originating from small sample misalignments on the sample rod. Background can be minimized by using samples with near cylindrical symmetry and using a microscope when mounting the sample on the sample rod.

Electromechanical coupling characteristics analysis of vertical stirred mill based on ECS-MBD-DEM

This paper focuses on the start-up and steady-state operation stages of a vertical stirred mill, and the electromechanical coupling characteristics are thoroughly investigated based on the ECS-MBD-DEM coupling method. Firstly, according to the driving and working principles of the vertical stirred mill, the electrical control system (ECS) and multibody dynamics (MBD) model of the vertical stirred mill are separately established. Subsequently, a discrete element method (DEM) model is developed for the grinding media inside the mill. On this basis, the ECS-MBD-DEM coupling model of the vertical stirred mill is constructed, and its feasibility is validated through experiments. Then, the pitch, screw diameter, grinding media filling, and mill rotation speed of the helical agitator are considered as influential factors, with average value and coefficient of variation used as evaluation indicators for the level and fluctuation of changes. The load torque and current amplitude during the start-up and steady-state stages of the vertical stirred mill are analysed separately based on the ECS-MBD-DEM coupling method. The results indicate that the pitch, screw diameter, and grinding media filling have a significant effect on the average value of load torque. The screw diameter, grinding media filling, and mill rotation speed significantly influence the coefficient of variation of the load torque. The mill speed has a significant effect on the average value and coefficient of variation of the current amplitude. Finally, the cumulative volume velocity difference is proposed as an evaluation indicator for the grinding efficiency in the annular region, and the impact of influential factors on it is discussed, the results show that the grinding media filling and mill speed have a significant impact on the cumulative volume velocity difference.

Individual Muscle Force Estimation in the Human Forearm Using Multi-Muscle MR Elastography (MM-MRE).

To establish the sensitivity of magnetic resonance elastography (MRE) to active muscle contraction in multiple muscles of the forearm. We combined MRE of forearm muscles with an MRI-compatible device, the MREbot, to simultaneously measure the mechanical properties of tissues in the forearm and the torque applied by the wrist joint during isometric tasks. We measured shear wave speed of thirteen forearm muscles via MRE in a series of contractile states and wrist postures and fit these outputs to a force estimation algorithm based on a musculoskeletal model. Shear wave speed changed significantly upon several factors, including whether the muscle was recruited as an agonist or antagonist (p = 0.0019), torque amplitude (p = <0.0001), and wrist posture (p = 0.0002). Shear wave speed increased significantly during both agonist (p = <0.0001) and antagonist (p = 0.0448) contraction. Additionally, there was a greater increase in shear wave speed at greater levels of loading. The variations due to these factors indicate the sensitivity to functional loading of muscle. Under the assumption of a quadratic relationship between shear wave speed and muscle force, MRE measurements accounted for an average of 70% of the variance in the measured joint torque. This study shows the ability of MM-MRE to capture variations in individual muscle shear wave speed due to muscle activation and presents a method to estimate individual muscle force through MM-MRE derived measurements of shear wave speed. MM-MRE could be used to establish normal and abnormal muscle co-contraction patterns in muscles of the forearm controlling hand and wrist function.

Analytical Calculation and Low-Order Component Optimization of Axial Electromagnetic Force for an Axial Flux Motor

The low-order high-amplitude component of axial electromagnetic force is the leading cause of electromagnetic vibration and noise of axial flux permanent magnet (AFPM) motors. In this paper, based on the analytical calculation of the axial electromagnetic force for a 20-pole 24-slot AFPM motor, the low-order axial electromagnetic force component is weakened by optimizing the motor’s electromagnetic structure. First, the three-dimensional (3-D) structural model of the motor is equated to a two-dimensional (2-D) analytical model, which is used to calculate the magnetic field generated by each of the armature winding and permanent magnet. Then, combined with the Maxwell tensor method, the axial electromagnetic force waveform is further obtained, and the target low-order high-amplitude component is extracted by 2-D Fourier analysis. Finally, taking this axial electromagnetic force component minimization as the target function of optimization, considering the output torque and ripple as constraints, the genetic algorithm is used to search for the optimal point by varying the structural parameters of the motor. The results show that the target low-order high-amplitude component of the axial electromagnetic force of the optimized motor is effectively suppressed, and the output torque ripple decreases with slightly increased torque amplitude, which provides a practical method for vibration and noise reduction of AFPM motors.

Исследование рассеяния энергии и жесткости сварных соединений стыковой сварки давлением

Introduction. When studying the energy dissipation associated with internal friction in a weld, it is extremely important to choose a measurement technique, since the reliability and integrity of the data obtained depends on it. At the same time, it is necessary to investigate the change in internal friction depending on the presence of defects in the weld. Of the variety of methods for non-destructive testing of joints obtained by pressure welding, only ultrasonic is currently used. However, lightly oxidized lacks of welding penetration are not detected, which can be detected only in the presence of other defects accompanying it. Compounds of dissimilar materials are not controlled by ultrasound at all. Therefore, the development of non-destructive testing methods for such compounds is very relevant. The purpose of the work: to find a procedure for testing the quality of a welded joint in metals and alloys that will be a quick and simple alternative to the known methods of non-destructive testing, by measuring the energy dissipation in the weld of the sample by the static hysteresis loop method. The method of investigation is non-destructive quality control of the welded joint in metals and alloys by measuring the energy dissipation in the weld of the sample by the static hysteresis loop method. Results and discussion. It is established that with an increase in the lacks of welding penetration, the energy dissipation increases at the same values of the torque amplitude under static loading conditions. The rigidity of the qualitative welded joints remains constant, and the joints with lacks of welding penetration decrease with increasing torque amplitude. The relationship of strength with stiffness and damping ability obtained by the static hysteresis loop method is preserved for various structural states of the sample material.

The coupling of tower-shadow effect and surge motion intensifies aerodynamic load variability in downwind floating offshore wind turbines

As the deployment of large-scale wind turbines expands into deeper waters, the downwind floating offshore wind turbine (FOWT) becomes an increasingly attractive prospect. Yet, the aerodynamic performance of these turbines, which is significantly impacted by both the tower-shadow effect and the complex six degrees of freedom (6 DOFs) platform motions, exhibits a complexity that surpasses that of traditional upwind floating or downwind fixed wind turbines. To thoroughly explore this complexity, this study employs computational fluid dynamics (CFD) using the unsteady, non-compressible Reynolds-averaged Navier-Stokes (RANS) method on a full-scale model of a downwind FOWT. Our investigation primarily focuses on the intertwining impacts of the tower-shadow effect and the platform's surge motion on the aerodynamic behavior of downwind FOWTs. The study reveals several key findings: the downwind FOWT exhibits comparable, if not superior, power-generation capabilities to prevailing upwind FOWTs; the surge motion significantly dictates both the fluctuation periods and amplitudes of rotor thrust and torque; the tower-shadow effect induces sudden reductions in rotor thrust and torque at a frequency three times that of the rotor rotation; and intriguingly, the magnitude of these sudden drops can be amplified or diminished by the surge motion. The maximum drop amplitude of torque reaches 120–150% the magnitude of the minimum drop amplitude during selected surge motions. This demonstrates that the coupling effects of the tower-shadow effect and surge motion add another layer of variability to the turbine's performance. In conclusion, downwind FOWTs present heightened variability in aerodynamic loads, underscoring the need to consider the potential consequences on power fluctuation and structural fatigue in turbine design and operation.

Finite Control Set Model Predictive Torque Control Considering Dynamic and Steady‐State Control Performance for SMPMSM Drives

In order to improve the dynamic and steady‐state performance of the finite control set model predictive torque controlled surface‐mounted permanent magnet synchronous motor drive system, a novel finite control set model predictive torque control (FCS‐MPTC) with different dynamic and steady‐state control schemes is proposed in this paper. When the SMPMSM drive system operates at transient state, the optimal basic voltage vector of inverter is the vector that minimizes torque tracking error, the proposed FCS‐MPTC achieves fast dynamic response based on the optimal torque control. When the system operates at steady state, the relative importance of torque to the stator flux amplitude is calculated based on the quantitative analysis of minimum staggered errors between motor torque and stator flux amplitude control objectives, then the priority weighting factors based on the relative importance are determined online adaptively, the optimal control of motor torque and stator flux amplitude is achieved simultaneously. Finally, the comparison of the experimental results of proposed FCS‐MPTC with different control methods is implemented and research conclusion is shown. © 2023 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

An Experimental and Numerical Evaluation of the Aerodynamic Performance of a UAV Propeller Considering Pitch Motion

Considering the vibration generated by a propeller-driven UAV or encountering gust, the propeller will perform a very complex follower motion. A pitch and rotating coupled motion is proposed in the present work that can take more complex unsteady performance of follower force than a regular fixed-point rotating motion. In order to evaluate the unsteady follower force and conduct parametric study, an extensive ground test bench was designed for this purpose where the whole test system was driven by a linear servo actuator and the follower force was measured by a 6-component balance. For CFD simulation, coupled motion in particular needs detailed unsteady aerodynamic model; therefore, a high-fidelity CFD-based study integrated with the overset mesh method was complemented to solve the unsteady fluid of varying conditions. The results suggest that a significant influence on unsteady follower force is observed, and the mean value of in-plane force does not equal to zero during the coupled motion process. Compared with the regular fixed-point rotation of propeller, the fluctuation frequency of follower force in present work couples the rotation and pitch motion frequencies. In addition, the oscillation amplitude of out-plane force and torque is positively related with the pitch frequency, pitch amplitude, and relative length from leading edge of wing to the rotation center. For example, the oscillation amplitude of 1-blade’s out-plane force and torque increases by 57.122% and 66.542% for the 5 Hz-5 deg case compared with the 5 Hz-3 deg case, respectively. However, the torque is not sensitive to frequency of pitch motion. The generally excellent agreement evident between the ground test and numerical simulation results is important as guidance for our future investigation on “dynamic” aerodynamic performance of a propeller-driven UAV.

Probing Accretion Physics with Gravitational Waves

Gravitational-wave observations of extreme mass ratio inspirals (EMRIs) offer the opportunity to probe the environments of active galactic nuclei (AGN) through the torques that accretion disks induce on the binary. Within a Bayesian framework, we study how well such environmental effects can be measured using gravitational wave observations from the Laser Interferometer Space Antenna (LISA). We focus on the torque induced by planetary-type migration on quasicircular inspirals, and use different prescriptions for geometrically thin and radiatively efficient disks. We find that LISA could detect migration for a wide range of disk viscosities and accretion rates, for both $\alpha$ and $\beta$ disk prescriptions. For a typical EMRI with masses $50M_\odot+10^6M_\odot$, we find that LISA could distinguish between migration in $\alpha$ and $\beta$ disks and measure the torque amplitude with $\sim 20\%$ relative precision. Provided an accurate torque model, we also show how to turn gravitational-wave measurements of the torque into constraints on the disk properties. Furthermore, we show that, if an electromagnetic counterpart is identified, the multimessenger observations of the AGN EMRI system will yield direct measurements of the disk viscosity. Finally, we investigate the impact of neglecting environmental effects in the analysis of the gravitational-wave signal, finding 3$\sigma$ biases in the primary mass and spin, and showing that ignoring such effects can lead to false detection of a deviation from general relativity. This work demonstrates the scientific potential of gravitational observations as probes of accretion-disk physics, accessible so far through electromagnetic observations only.

Torque Improvement of Spoke-type Permanent Magnet Motor with Auxiliary Stator Using Harmonic Current Control Strategy

The spoke-type permanent magnet motor with auxiliary stator exhibits high torque performance owing to the flux focus effects. To further improve its torque density, this paper proposes a control method by using harmonic current strategy. Based on the theoretical analysis, a 3-D torque look-up table by dq-axis current and electrical angle is established with the aid of the finite element method (FEM). The maximum torque per ampere curve at each rotor position is identified and summarized to adequately indicate the relationship between torque and current amplitude of the motor. Through theoretical derivation, it is concluded that the minimum torque cost curve is the contour line of ∂Te/∂i <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , which can be employed to identify the harmonic current for torque density improvement. Compared to traditional strategies, the proposed control strategy can increase torque density of forward and reverse torque by 1.22% and 1.40%, respectively. The experimental results verify the analysis and simulation results, as well as prove the effectiveness of the proposed strategy.

Three Voltage Vector Duty Cycle Optimization Strategy of the Permanent Magnet Synchronous Motor Driving System for New Energy Electric Vehicles Based on Finite Set Model Predictive Control

Faced with the increasingly serious energy crisis and environmental pollution problems, traditional internal combustion engine vehicles are receiving more and more resistance, which has rapidly promoted the development of new energy electric vehicles. Permanent magnet synchronous motors are widely used in new energy electric vehicles and in other fields because of their simple structure, light weight, small size, and high power density. With the continuous advancement of production technology, the requirements of accuracy, rapidity, and stability in permanent magnet synchronous motor systems have gradually increased. Among many advanced control technologies, this paper proposes an optimized model predictive torque control strategy based on voltage vector expansion. This strategy involves the construction of a reference stator flux linkage vector based on the analytical relationship between electromagnetic torque, reference stator flux linkage amplitude, and rotor flux linkage and the transfer of the separate control of electromagnetic torque and flux linkage amplitude into flux linkage vector control. At the same time, the optimal duty cycle corresponding to the two adjacent extended voltage vectors and the zero vector is calculated according to geometric relationships so as to realize the three voltage vector duty cycle optimization control. Experimental results show the effectiveness and superiority of the proposed strategy.

Perceived Discomfort and Voluntary Activation of Quadriceps Muscle Assessed with Interpolated Paired or Triple Electrical Stimuli.

Voluntary drive of the exercising muscle is usually assessed with the interpolated twitch technique (ITT), using paired supramaximal electrical stimuli. The aim of this study was to directly compare voluntary activation (VA) of the quadriceps muscle (QM) measured with the ITT, using paired and triple electrical stimuli during maximal voluntary isometric contraction (MVIC). In addition, perceived discomfort was compared with the use of paired and triple electrical stimuli during ITT. Ten healthy participants (23.6 ± 1.6 years) were included. They performed four MVIC, with paired or triple stimuli, in random order. MVIC torque, superimposed evoked torque, evoked torque at rest, VA, and visual analogue scale for pain (VAS-pain), were analysed. The amplitude of the triplet-evoked torque was higher than doublet-evoked torque, i.e., the signal-to-noise ratio increased. However, the differences between the estimation of VA with paired and triple stimuli were not significant (p = 0.136). Triple stimuli yielded higher VAS-pain scores than paired stimuli (p = 0.016). The limits of agreement for the VA using the Bland-Altman method were 7.66/0.629. It seems that the use of additional electrical stimuli is not a recommended solution for the evaluation of VA, because the advantages (i.e., better signal-to-noise ratio) do not outweigh the disadvantages (i.e., an increase in pain).