Assessment of Neuromuscular Function Using Percutaneous Electrical Nerve Stimulation

Mechanisms underlying altered neuromuscular function in people with DPN

Diabetes alters numerous physiological functions and can lead to disastrous consequences in the long term. Neuromuscular function is particularly affected and is impacted early, offering an opportunity to detect the onset of diabetes-related dysfunctions and follow the advancement of the disease. The role of physical training for counteracting the deleterious effects of diabetes is well accepted but at the same time, it appears difficult to reliably assess the effects of exercise on functional capacity in patients with diabetic peripheral neuropathy (DPN). In this paper, we will review the specific characteristics of various neuromuscular dysfunctions associated with diabetes according to the DPN presence or not, and their changes over time. We present several propositions regarding the onset of neuromuscular alterations in people with diabetes compared to people with DPN. It appears that motor unit loss and neuromuscular transmission impairment are among the main mechanisms explaining the considerable degradation of neuromuscular function in the transition from a diabetic to neuropathic state. Rate of force development and contractile properties could start to decrease with the onset of preferential type II fiber atrophy, commonly reported in people with DPN. Finally, M_max amplitude could decrease with neuromuscular fatigue only in people with DPN, reflecting the fatigue-related neuromuscular transmission impairment reported in people with DPN. In this review, we show that the different neuromuscular parameters are altered at different stages of diabetes, according to the presence of DPN or not. The precise evaluation of these parameters might participate in adapting the physical training prescription.

Lower-Extremity Neuromuscular Function Following Concussion: A Preliminary Examination

CONTEXT

Neuromuscular function is altered acutely following concussion and theoretically linked to the subsequent postconcussion musculoskeletal injury risk. Existing research has only examined voluntary muscle activation, limiting mechanistic understanding. Therefore, our study aimed to examine voluntary and involuntary muscle activation between college-aged, concussed individuals when symptom-free and healthy matched controls.

DESIGN

Prospective, cross-sectional cohort laboratory study.

METHODS

Concussed and healthy participants (n = 24; 58% male, age: 19.3 [1.1] y, mass: 70.3 [16.4] kg, height: 177.3 [12.7] cm) completed the superimposed burst (SB) neuromuscular assessment on their dominant limb within 72 hours after self-reporting asymptomatic (22.4 [20.2] d postinjury). Unnormalized and bodyweight-normalized quadriceps maximal voluntary isometric contraction torque (in newton meters), unnormalized and bodyweight-normalized electrically stimulated SB torque, pain (numeric 1-10) during SB, and the central activation ratio (in percentage) were assessed via the SB. Parametric and nonparametric analyses, 95% confidence intervals (95% CIs), and Hedges g (parametric) and Spearman ρ (nonparametric) effect sizes were used to examine group differences (α = .05).

RESULTS

The maximal voluntary isometric contraction torque (concussed: 635.60 N·m [300.93] vs control: 556.27 N·m [182.46]; 95% CI, -131.36 to 290.02; P = .443; d = 0.33), SB torque (concussed: 203.22 N·m [97.17], control: 262.85 N·m [159.07]; 95% CI, -171.22 to 51.97; P = .280; d = -0.47), and central activation ratio (concussed: 72.16% [17.16], control: 70.09% [12.63]; 95% CI, -10.68 to 14.83; P = .740; d = 0.14) did not differ between the concussed and control groups regardless of bodyweight normalization (P ≥ .344). Pain during the SB was significantly higher with a medium effect for participants with a concussion versus healthy controls (concussed: median = 7, control: median = 5; P = .046; ρ = -0.42).

DISCUSSION

These findings suggest concussed participants do not have statistically altered voluntary or involuntary quadricep neuromuscular function once asymptomatic compared with controls. Therefore, the elevated postconcussion musculoskeletal injury risk may not be attributed to lower-extremity muscle activation. Concussed participants displayed greater pain perception during the SB, which suggests somatosensory or perception changes requiring further examination.

The impact of submaximal fatiguing exercises on the ability to generate and sustain the maximal voluntary contraction

Neuromuscular fatigability is a failure to produce or maintain a required torque, and commonly quantified with the decrease of maximal torque production during a few seconds-long maximal voluntary contraction (MVC). The literature shows that the MVC reduction after exercises with different torque-time integral (TTI), is often similar. However, it was shown that after a fatiguing exercise, the decline in the capacity to sustain the maximal voluntary contraction for 1 min (MVC1-MIN) differs from the decrease in the capacity to perform a brief-MVC, suggesting that this latter can only partially assess neuromuscular fatigability. This study aims to highlight the relevance of using a sustained MVC to further explore the neuromuscular alterations induced by fatiguing exercises with different TTI. We used two contraction intensities (i.e., 20% and 40% MVC) to modulate the TTI, and two exercise modalities [i.e., voluntary (VOL) and electrical induced (NMES)], since the letter are known to be more fatiguing for a given TTI. Thirteen subjects performed a plantar-flexors MVC1-MIN before and after the fatiguing exercises. A similar MVC loss was obtained for the two exercise intensities despite a greater TTI at 40% MVC, regardless of the contraction modality. On the other hand, the torque loss during MVC1-MIN was significantly greater after the 40% compared to 20% MVC exercise. These findings are crucial because they demonstrate that maximal torque production and sustainability are two complementary features of neuromuscular fatigability. Hence, MVC1-MIN assessing simultaneously both capacities is essential to provide a more detailed description of neuromuscular fatigability.

Effects of Ultrasound-Guided Nerve Stimulation Targeting Peripheral Nerve Tissue on Pain and Function: A Scoping Review

This paper assesses the effects of percutaneous electrical nerve stimulation (PENS) on pain- and function-related outcomes by means of a scoping review of studies with single cases, case-series, quasi-experimental, and randomized or non-randomized trial designs. We consulted the PubMed, MEDLINE and EMBASE databases. Data were extracted by two reviewers. The methodological quality of studies was assessed using the Physiotherapy Evidence Database (PEDro) scale for experimental studies and the Joanna Briggs Institute (JBI) tool for case reports or cases series. Mapping of the results included: (1), description of included studies; (2), summary of results; and, (3), identification of gaps in the existing literature. Eighteen articles (five randomized controlled trials, one trial protocol, nine case series and three case reports) were included. The methodological quality of the papers was moderate to high. The conditions included in the studies were heterogeneous: chronic low back pain, lower limb pain after lumbar surgery, chronic post-amputation pain, rotator cuff repair, foot surgery, knee arthroplasty, knee pain, brachial plexus injury, elbow pain and ankle instability. In addition, one study included a healthy athletic population. Interventions were also highly heterogeneous in terms of sessions, electrical current parameters, or time of treatment. Most studies observed positive effects of PENS targeting nerve tissue against the control group; however, due to the heterogeneity in the populations, interventions, and follow-up periods, pooling analyses were not possible. Based on the available literature, PENS interventions targeting peripheral nerves might be considered as a potential therapeutic strategy for improving pain-related and functional outcomes. Nevertheless, further research considering important methodological quality issues (e.g., inclusion of control groups, larger sample sizes and comparatives between electric current parameters) are needed prior to recommending its use in clinical practice.

Understanding fatigue in primary biliary cholangitis: From pathophysiology to treatment perspectives

Fatigue is considered one of the most frequent and debilitating symptoms in primary biliary cholangitis (PBC), affecting over 50% of PBC patients. One in five patients with PBC suffer from severe fatigue, which significantly impairs quality of life. Fatigue is made up of a central and a peripheral component, whose pathophysiology is still greatly unresolved. Central fatigue is characterised by a lack of self-motivation and can manifest both in physical and mental activities (lack of intention). Peripheral fatigue includes neuromuscular dysfunction and muscle weakness (lack of ability). Peripheral fatigue could be explained by an excessive deviation from aerobic to anaerobic metabolism leading to excessive lactic acid accumulation and therefore accelerated decline in muscle function and prolonged recovery time. As opposed to itching, and with the exception of end-stage liver disease, fatigue is not related to disease progression. The objective of this review is to outline current understanding regarding the pathophysiology of fatigue, the role of comorbidities and contributing factors, the main tools for fatigue assessment, the failed therapeutic options, and future treatment perspectives for this disabling symptom. Since fatigue is an extremely common and debilitating symptom and there is still no licensed therapy for fatigue in PBC patients, further research is warranted to understand its causative mechanisms and to find an effective treatment.

Cardiometabolic and neuromuscular analyses of the sit-to-stand transition to question its role in reducing sedentary patterns

To counteract the detrimental health effect of sitting all day long, it has been suggested to regularly break sitting time by standing. However, while the difference in energy expenditure, neuromuscular and/or cardiovascular demand of various postures from lying, sitting, and standing is well documented, little is known regarding the dynamic changes occurring during the sit-to-stand transition itself. The aim of the present study was then to describe the cardiometabolic and neuromuscular responses from sitting to standing and specifically during the time-course of this transition. Twelve healthy young participants were asked to perform standardized raises from sitting posture, while cardiometabolic (cardiorespiratory and hemodynamic variables) and neuromuscular (calf muscles' myoelectrical activity, spinal and supraspinal excitabilities) parameters were monitored. As a result, while there was a rapid adaptation for all the systems after rising, the neuromuscular system displayed the faster adaptation (~ 10 s), then hemodynamic (~ 10 to 20 s) and finally the metabolic variables (~ 30 to 40 s). Oxygen uptake, energy expenditure, ventilation, and heart rate were significantly higher and stroke volume significantly lower during standing period compared to sitting one. In calf muscles, spinal excitability (H-reflexes), was lowered by the sit-to-stand condition, while supraspinal drive (V-wave) was similar, indicating different cortico-spinal balance from sitting to standing. Although very heterogenous among participants in terms of magnitude, the present results showed a rapid adaptation for all the systems after rising and the health benefit, notably in terms of energy expenditure, appears rather modest, even if non negligeable.

Temporal Profile of Descending Cortical Modulation of Spinal Excitability: Group and Individual-Specific Effects

Sensorimotor control is modulated through complex interactions between descending corticomotor pathways and ascending sensory inputs. Pairing sub-threshold transcranial magnetic stimulation (TMS) with peripheral nerve stimulation (PNS) modulates the Hoffmann’s reflex (H-reflex), providing a neurophysiologic probe into the influence of descending cortical drive on spinal segmental circuits. However, individual variability in the timing and magnitude of H-reflex modulation is poorly understood. Here, we varied the inter-stimulus interval (ISI) between TMS and PNS to systematically manipulate the relative timing of convergence of descending TMS-induced volleys with respect to ascending PNS-induced afferent volleys in the spinal cord to: (1) characterize effective connectivity between the primary motor cortex (M1) and spinal circuits, mediated by both direct, fastest-conducting, and indirect, slower-conducting descending pathways; and (2) compare the effect of individual-specific vs. standard ISIs. Unconditioned and TMS-conditioned H-reflexes (24 different ISIs ranging from −6 to 12 ms) were recorded from the soleus muscle in 10 able-bodied individuals. The magnitude of H-reflex modulation at individualized ISIs (earliest facilitation delay or EFD and individual-specific peak facilitation) was compared with standard ISIs. Our results revealed a significant effect of ISI on H-reflex modulation. ISIs eliciting earliest-onset facilitation (EFD 0 ms) ranged from −3 to −5 ms across individuals. No difference in the magnitude of facilitation was observed at EFD 0 ms vs. a standardized short-interval ISI of −1.5 ms. Peak facilitation occurred at longer ISIs, ranging from +3 to +11 ms. The magnitude of H-reflex facilitation derived using an individual-specific peak facilitation was significantly larger than facilitation observed at a standardized longer-interval ISI of +10 ms. Our results suggest that unique insights can be provided with individual-specific measures of top-down effective connectivity mediated by direct and/or fastest-conducting pathways (indicated by the magnitude of facilitation observed at EFD 0 ms) and other descending pathways that encompass relatively slower and/or indirect connections from M1 to spinal circuits (indicated by peak facilitation and facilitation at longer ISIs). By comprehensively characterizing the temporal profile and inter-individual variability of descending modulation of spinal reflexes, our findings provide methodological guidelines and normative reference values to inform future studies on neurophysiological correlates of the complex array of descending neural connections between M1 and spinal circuits.

Stand Up to Excite the Spine: Neuromuscular, Autonomic, and Cardiometabolic Responses During Motor Imagery in Standing vs. Sitting Posture

Motor imagery (MI) for health and performance strategies has gained interest in recent decades. Nevertheless, there are still no studies that have comprehensively investigated the physiological responses during MI, and no one questions the influence of low-level contraction on these responses. Thus, the aim of the present study was to investigate the neuromuscular, autonomic nervous system (ANS), and cardiometabolic changes associated with an acute bout of MI practice in sitting and standing condition. Twelve young healthy males (26.3 ± 4.4 years) participated in two experimental sessions (control vs. MI) consisting of two postural conditions (sitting vs. standing). ANS, hemodynamic and respiratory parameters, body sway parameters, and electromyography activity were continuously recorded, while neuromuscular parameters were recorded on the right triceps surae muscles before and after performing the postural conditions. While MI showed no effect on ANS, the standing posture increased the indices of sympathetic system activity and decreased those of the parasympathetic system (p < 0.05). Moreover, MI during standing induced greater spinal excitability compared to sitting posture (p < 0.05), which was accompanied with greater oxygen consumption, energy expenditure, ventilation, and lower cardiac output (p < 0.05). Asking individuals to perform MI of an isometric contraction while standing allows them to mentally focus on the motor command, not challenge balance, and produce specific cardiometabolic responses. Therefore, these results provide further evidence of posture and MI-related modulation of spinal excitability with additional autonomic and cardiometabolic responses in healthy young men.

The effects of supervision on three different exercises modalities (supervised vs. home vs. supervised+home) in older adults: Randomized controlled trial protocol

BACKGROUND

Multicomponent physical exercise programs are a viable strategy for treating physical decline resulting from the aging process in older populations and can be applied in supervised and home-based modalities. However, the magnitude of the intervention effects in terms of physical function development may vary according to the modalities application due to different supervision degrees.

OBJECTIVE

This study aims to compare the effects of supervision in a multicomponent exercise program in different application modalities (supervised vs. home vs. supervised+home) in neuromuscular adaptations, muscle strength, gait, physical function, and quality of life, analyzing the differences between intensity, volume, and density of home and supervised sessions in community older adults.

METHODS

This protocol is a randomized controlled clinical trial with a sample of 66 older adults divided into three groups: supervised exercise (SUP = 22), home-based exercise (HB = 22), and supervised plus home-based exercise (SUP+HB = 22). The multicomponent exercise program will last 12 weeks, three times per week, for 60 min per session and include warm-up, balance, muscle-strengthening, gait, and flexibility exercises. The study's primary outcomes will be neuromuscular function, composed of the assessment of muscle isokinetic strength, muscle architecture, and neuromuscular electrical activation. The secondary outcome will be physical function, usual and maximum gait speed with and without dual-task, and quality of life. All outcomes will be assessed at baseline and post-intervention (week 12).

CONCLUSION

This study will be the first clinical trial to examine the effects of different supervision levels on home-based exercises compared to supervised protocols. The results of this study will be essentials for planning coherent and viable home-based programs for older adults.

TRIAL REGISTRATION

Brazilian Registry of Clinical Trials. Number RBR- 7MZ2KR. https://apps.who.int/trialsearch/Trial2.aspx?TrialID=RBR-7mz2kr.

No effect of passive stretching on neuromuscular function and maximum force-generating capacity in the antagonist muscle

Purpose

The present study investigated whether or not passive stretching increases the force-generating capacity of the antagonist muscle, and the possible neuromuscular mechanisms behind.

Methods

To this purpose, the neuromuscular function accompanying the force-generating capacity was assessed in 26 healthy male volunteers after passive stretching and in a control session. Before and after passive intermittent static stretching of the plantar flexors consisting of five sets × 45 s + 15 s-rest, maximum voluntary isometric contraction (MVC) and surface electromyographic root mean square (sEMG RMS) were measured in the tibialis anterior (the antagonist muscle). Additionally, evoked V wave, H-reflex, and M wave were elicited by nerve stimulation at rest and during MVC. Ankle range of motion (ROM) and plantar flexors MVC and EMG RMS were measured to check for the effectiveness of the stretching manoeuvre.

Results

No change in MVC [p = 0.670; effect size (ES) − 0.03] and sEMG RMS/M wave during MVC (p = 0.231; ES − 0.09) was observed in the antagonist muscle after passive stretching. Similarly, no change in V wave (p = 0.531; ES 0.16), H-reflex at rest and during MVC (p = 0.656 and 0.597; ES 0.11 and 0.23, respectively) and M wave at rest and during MVC (p = 0.355 and 0.554; ES 0.04 and 0.01, respectively) was observed. An increase in ankle ROM (p < 0.001; ES 0.55) and a decrease in plantar flexors MVC (p < 0.001; ES − 1.05) and EMG RMS (p < 0.05; ES − 1.72 to − 0.13 in all muscles) indicated the effectiveness of stretching protocol.

Conclusion

No change in the force-generating capacity and neuromuscular function of the antagonist muscle after passive stretching was observed.

Prior Upper Body Exercise Impairs 4-km Cycling Time-Trial Performance Without Altering Neuromuscular Function

Purpose: This study investigated the effects of previous exhaustive upper body exercise on performance and neuromuscular fatigue following a 4-km cycling time-trial (4-km TT). Methods: Eight recreational cyclists performed a 4-km TT with (ARM_PRE) or without (CONTR) a previous arm-crank maximal incremental test. In each experimental session, neuromuscular fatigue was evaluated with a series of electrically evoked and maximal voluntary isometric contractions (MVC). Oxygen uptake ( V ˙ O₂), heart rate, electromyographic muscle activity (EMG_RMS) and rating of perceived exertion (RPE) were also recorded throughout the 4-km TT. Results: The average power output during the 4-km TT was reduced (P = .027) for the ARM_PRE (299 ± 59 W) group, compared with CONTR (310 ± 59 W) and overall performance in 4-km TT was impaired (P = .021) in ARM_PRE (382 ± 28 s) compared with CONTR (376 ± 27 s). The decrease observed in MVC (P = .033) and potentiated peak twitch force (P = .004) at post-TT were similar between the ARM_PRE and CONTR conditions (P = .739 and P = .493, respectively). There was no (P = .619) change in voluntary activation at post-TT between conditions. V ˙ O₂, EMG_RMS and RPE measured throughout the 4-km TT were not significantly different between the conditions (P = .558, P = .558 and P = .940, respectively). The rate of RPE change relative to power output average and heart rate was higher (P = .030 and P = .013, respectively) in ARM_PRE (0.031 ± 0.018 AU/W and 168 ± 8 bpm) than CONTR (0.022 ± 0.010 AU/W and 161 ± 7 bpm). Conclusion: These results suggest that impaired performance in ARM_PRE was mostly due to pronounced perception of effort rather than neuromuscular fatigue.

Mechanism of Peripheral Nerve Stimulation in Chronic Pain

INTRODUCTION

With the advancement of technology, peripheral nerve stimulation (PNS) has been increasingly used to treat various chronic pain conditions. Its origin is based on the gate control theory postulated by Wall and Melzack in 1965. However, the exact mechanism behind PNS' analgesic effect is largely unknown. In this article, we performed a comprehensive literature review to overview the PNS mechanism of action.

DESIGN

A comprehensive literature review on the mechanism of PNS in chronic pain.

METHODS

Comprehensive review of the available literature on the mechanism of PNS in chronic pain. Data were derived from database searches of PubMed, Scopus, and the Cochrane Library and manual searches of bibliographies and known primary or review articles.

RESULTS

Animal, human, and imaging studies have demonstrated the peripheral and central analgesic mechanisms of PNS by modulating the inflammatory pathways, the autonomic nervous system, the endogenous pain inhibition pathways, and involvement of the cortical and subcortical areas.

CONCLUSIONS

Peripheral nerve stimulation exhibits its neuromodulatory effect both peripherally and centrally. Further understanding of the mechanism of PNS can help guide stimulation approaches and parameters to optimize the use of PNS.

Central and Peripheral Shoulder Fatigue Pre-screening Using the Sigma-Lognormal Model: A Proof of Concept

Background

Clinical tests for detecting central and peripheral shoulder fatigue are limited. The discrimination of these two types of fatigue is necessary to better adapt recovery intervention. The Kinematic Theory of Rapid Human Movements describes the neuromotor impulse response using lognormal functions and has many applications in pathology detection. The ideal motor control is modeled and a change in the neuromuscular system is reflected in parameters extracted according to this theory.

Objective

The objective of this study was to assess whether a shoulder neuromuscular fatigue could be detected through parameters describing the theory, if there is the possibility to discriminate central from peripheral fatigue, and which handwriting test gives the most relevant information on fatigue.

Methods

Twenty healthy participants performed two sessions of fast stroke handwriting on a tablet, before and after a shoulder fatigue. The fatigue was in internal rotation for one session and in external rotation during the other session. The drawings consisted of simple strokes, triangles, horizontal, and vertical oscillations. Parameters of these strokes were extracted according to the Sigma–Lognormal model of the Kinematic Theory. The evolution of each participant was analyzed through a U-Mann–Whitney test for individual comparisons. A Hotelling’s T²-test and a U-Mann–Whitney test were also performed on all participants to assess the group evolution after fatigue. Moreover, a correlation among parameters was calculated through Spearman coefficients to assess intrinsic parameters properties of each handwriting test.

Results

Central and peripheral parameters were statistically different before and after fatigue with a possibility to discriminate them. Participants had various responses to fatigue. However, when considering the group, parameters related to the motor program execution showed significant increase in the handwriting tests after shoulder fatigue. The test of simple strokes permits to know more specifically where the fatigue comes from, whereas the oscillations tests were the most sensitive to fatigue.

Conclusion

The results of this study suggest that the Sigma–Lognormal model of the Kinematic Theory is an innovative approach for fatigue detection with discrimination between the central and peripheral systems. Overall, there is a possibility to implement the setting for clinics and sports personalized follow-up.

Greater fatigability in knee-flexors vs. knee-extensors after a standardized fatiguing protocol

The present study aimed to investigate the effects of a standardized fatiguing protocol on central and peripheral fatigue in knee-flexors and knee-extensors. Thirteen healthy men (age: 23 ± 3 years; height: 1.78 ± 0.09 m; body-mass: 73.6 ± 9.2 kg) volunteered for the present study. Maximal voluntary contraction (MVC), Electromyography (EMG) activity, voluntary activation level (VAL) as an index of central fatigue and twitch potentiation as an index of peripheral fatigue were measured before and after the fatiguing protocol. The fatiguing protocol consisted of a 0.6 duty-cycle to exhaustion (6 s isometric contraction, 4 s recovery) at 70% MVC. After the fatiguing protocol, MVC decreased in both (Effect-size (ES) = 1.14) and knee-extensors (ES = 1.14), and EMG activity increased in both knee-flexors (ES = 2.33) and knee-extensors (ES = 1.54). Decreases in VAL occurred in knee-flexors (ES = 0.92) but not in knee-extensors (ES = 0.04). Decreases in potentiation occurred in both knee-flexors (ES = 0.84) and knee-extensors (ES = 0.58). The greater central occurrence of fatigue in knee-flexors than in knee-extensors may depend on the different muscle morphology and coupled with a greater tolerance to fatigue in knee-extensors. The present data add further insight to the complicated knee-flexors-to-knee-extensors strength relationship and the mechanisms behind the different occurrence of fatigue.

Effect of knee angle on neuromuscular assessment of plantar flexor muscles: A reliability study

INTRODUCTION

This study aimed to determine the intra- and inter-session reliability of neuromuscular assessment of plantar flexor (PF) muscles at three knee angles.

METHODS

Twelve young adults were tested for three knee angles (90°, 30° and 0°) and at three time points separated by 1 hour (intra-session) and 7 days (inter-session). Electrical (H reflex, M wave) and mechanical (evoked and maximal voluntary torque, activation level) parameters were measured on the PF muscles. Intraclass correlation coefficients (ICC) and coefficients of variation were calculated to determine intra- and inter-session reliability.

RESULTS

The mechanical measurements presented excellent (ICC>0.75) intra- and inter-session reliabilities regardless of the knee angle considered. The reliability of electrical measurements was better for the 90° knee angle compared to the 0° and 30° angles.

CONCLUSIONS

Changes in the knee angle may influence the reliability of neuromuscular assessments, which indicates the importance of considering the knee angle to collect consistent outcomes on the PF muscles.

Short vs. long pulses for testing knee extensor neuromuscular properties: does it matter?

PURPOSE

The present study aimed at comparing knee extensor neuromuscular properties determined with transcutaneous electrical stimulation using two pulse durations before and after a standardized fatigue protocol.

METHODS

In the first sub-study, 19 healthy participants (ten women and nine men; 28 ± 5 years) took part to two separate testing sessions involving the characterization of voluntary activation (twitch interpolation technique), muscle contractility (evoked forces by single and paired stimuli), and neuromuscular propagation (M-wave amplitude from vastus lateralis and vastus medialis muscles) obtained at supramaximal intensity with a pulse duration of either 0.2 or 1 ms. The procedures were identical in the second sub-study (N = 11), except that neuromuscular properties were also evaluated after a standardized fatiguing exercise. Electrical stimulation was delivered through large surface electrodes positioned over the quadriceps muscle and a visual analog scale was used to evaluate the discomfort to paired stimuli evoked at rest.

RESULTS

There was no difference between pulse durations in the estimates of voluntary activation, neuromuscular propagation, and muscle contractility both in the non-fatigued and fatigued states. The discomfort associated with supramaximal paired electrical stimuli was also comparable between the two pulse durations.

CONCLUSIONS

It appears that 0.2- and 1-ms-long pulses provide a comparable evaluation of knee extensor neuromuscular properties.