Acute effects of conventional versus wide-pulse neuromuscular electrical stimulation on quadriceps evoked torque and neuromuscular function

PURPOSE

The effectiveness of a neuromuscular electrical stimulation (NMES) program is proportional to the level of evoked torque, which can be achieved with either conventional or wide-pulse stimulations. The aim of this study was to compare evoked torque, objective fatigability, and related peripheral and central alterations, as well as changes in central nervous system (CNS) excitability induced by an acute session of conventional versus wide-pulse NMES.

METHODS

Seventeen young men underwent three 20-min NMES sessions: conventional (0.2 ms/50 Hz), wide-pulse at 50 Hz (1 ms/50 Hz), and wide-pulse at 100 Hz (1 ms/100 Hz). Neuromuscular measurements (i.e., maximal voluntary contraction, voluntary activation, evoked responses to femoral nerve stimulation, and CNS excitability) were performed on the right quadriceps femoris muscle before and after each NMES session. CNS excitability was measured using transcranial magnetic, thoracic, and transcutaneous spinal cord stimulations.

RESULTS

The level of evoked torque was not significantly different between conventional and wide-pulse protocols applied at the maximal tolerable current intensity. All NMES protocols induced objective fatigability (~14% decrease in maximal voluntary contraction torque, p < 0.001) associated with peripheral (decrease in doublet torque and potentiated M-wave amplitude, p = 0.002 and p < 0.001, respectively) but not central (unchanged voluntary activation, p = 0.79) alterations. However, these acute changes did not differ between NMES protocols and none of the NMES protocols modified markers of CNS excitability.

CONCLUSION

These results may allow to conjecture that chronic effects and treatment effectiveness could be comparable between conventional and wide-pulse NMES.

Acute effects of quadriceps muscle versus tendon prolonged local vibration on force production capacities and central nervous system excitability

PURPOSE

The present study aimed to directly compare the effects of 30 min muscle (VIB_muscle) vs. tendon (VIB_tendon) local vibration (LV) to the quadriceps on maximal voluntary isometric contraction (MVIC) and rate of torque development (RTD) as well as on central nervous system excitability (i.e. motoneuron and cortical excitability).

METHODS

Before (PRE) and immediately after (POST) LV applied to the quadriceps muscle or its tendon, we investigated MVIC and RTD (STUDY #1; n = 20) or vastus lateralis (VL), vastus medialis (VM) and rectus femoris (RF) electromyography responses to thoracic electrical stimulation (TMEPs; motoneuron excitability) and transcranial magnetic stimulation (MEPs; corticospinal excitability) (STUDY #2; n = 17). MEP/TMEP ratios were further calculated to quantify changes in cortical excitability.

RESULTS

MVIC decreased at POST (P = 0.017) without any difference between VIB_tendon and VIB_muscle, while RTD decreased for VIB_tendon (P = 0.013) but not VIB_muscle. TMEP amplitudes were significantly decreased for all muscles (P = 0.014, P < 0.001 and P = 0.004 for VL, VM and RF, respectively) for both LV sites. While no changes were observed for MEP amplitude, MEP/TMEP ratios increased at POST for VM and RF muscles (P = 0.009 and P = 0.013, respectively) for both VIB_tendon and VIB_muscle.

CONCLUSION

The present results suggest that prolonged muscle and tendon LV are similarly effective in modulating central nervous system excitability and decreasing maximal force. Yet, altered explosive performance after tendon but not muscle LV suggests greater neural alterations when tendons are vibrated.

Fatigue, physical activity and quality of life in people self-reporting symptoms of chronic venous disease

OBJECTIVE

The aim of this study was to quantify fatigue and quality of life (QoL) in people self-reporting chronic venous disease (CVD) symptoms or at risk of CVD within a large cohort representative of the French population. The relationship between self-reported physical activity and both fatigue and QoL was also investigated. We hypothesised that a greater fatigue and impaired QoL would exist in participants self-reporting CVD symptoms, with the impairments being attenuated in those with greater level of physical activity.

METHODS

Using a web-based, custom and adaptive survey, 3,008 participants were asked to self-report the presence of common symptoms and risk factors of CVD. Fatigue, QoL and physical activity were assessed using the Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F) scale, the Chronic Venous Insufficiency Quality of Life Questionnaire (CIVIQ-14) and the Godin-Shepard Leisure-Time Physical Activity Questionnaire (GSLTPAQ), respectively.

RESULTS

32% of the participants were categorized as having CVD symptoms whereas 50% were categorized as at risk of CVD. Fatigue was greater in participants with CVD symptoms than non-CVD participants (p < 0.001), with the score of participants at risk of CVD being intermediate (p ≤ 0.001). QoL was more impaired in participants with CVD symptoms compared to participants at risk of CVD (p < 0.001). In participants with CVD symptoms, there were relationships between fatigue and QoL (p < 0.001) and between physical activity and fatigue (p < 0.001). Despite the relationship between physical activity and QoL not reaching significance (p = 0.067), a lower QoL was found in insufficiently active as compared to active (p < 0.001) and moderately active (p < 0.001) participants with CVD symptoms.

CONCLUSIONS

Participants self-reporting CVD symptoms suffer from greater fatigue and impaired QoL. In this population, a higher level of physical activity is associated with reduced fatigue and a tendency toward improved QoL.

Local vibration training improves the recovery of quadriceps strength in early rehabilitation after anterior cruciate ligament reconstruction: A feasibility randomised controlled trial

BACKGROUND

After anterior cruciate ligament reconstruction (ACLR), quadriceps strength must be maximised as early as possible.

OBJECTIVES

We tested whether local vibration training (LVT) during the early post-ACLR period (i.e., ∼10 weeks) could improve strength recovery.

METHODS

This was a multicentric, open, parallel-group, randomised controlled trial. Thirty individuals attending ACLR were randomised by use of a dedicated Web application to 2 groups: vibration (standardised rehabilitation plus LVT, n=16) or control (standardised rehabilitation alone, n=14). Experimenters, physiotherapists and participants were not blinded. Both groups received 24 sessions of standardised rehabilitation over ∼10 weeks. In addition, the vibration group received 1 hour of vibration applied to the relaxed quadriceps of the injured leg at the end of each rehabilitation session. The primary outcome - maximal isometric strength of both injured and non-injured legs (i.e., allowing for limb asymmetry measurement) - was evaluated before ACLR (PRE) and after the 10-week rehabilitation (POST).

RESULTS

Seven participants were lost to follow-up, so data for 23 participants were used in the complete-case analysis. For the injured leg, the mean (SD) decrease in maximal strength from PRE to POST was significantly lower for the vibration than control group (n=11, -16% [10] vs. n=12, -30% [11]; P=0.0045, Cohen's d effect size=1.33). Mean PRE-POST change in limb symmetry was lower for the vibration than control group (-19% [11] vs. -29% [13]) but not significantly (P=0.051, Cohen's d effect size=0.85).

CONCLUSION

LVT improved strength recovery after ACLR. This feasibility study suggests that LVT applied to relaxed muscles is a promising modality of vibration therapy that could be implemented early in ACLR.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT02929004.

Sex Differences in Neuromuscular Fatigue and Changes in Cost of Running after Mountain Trail Races of Various Distances

INTRODUCTION

Women have been shown to experience less neuromuscular fatigue than men in knee extensors (KE) and less peripheral fatigue in plantar flexors (PF) after ultratrail running, but it is unknown if these differences exist for shorter trail running races and whether this may impact running economy. The purpose of this study was to characterize sex differences in fatigability over a range of running distances and to examine possible differences in the postrace alteration of the cost of running (Cr).

METHODS

Eighteen pairs of men and women were matched by performance after completing different races ranging from 40 to 171 km, divided into SHORT versus LONG races (<60 and >100 km, respectively). Neuromuscular function and Cr were tested before and after each race. Neuromuscular function was evaluated on both KE and PF with voluntary and evoked contractions using electrical nerve (KE and PF) and transcranial magnetic (KE) stimulation. Oxygen uptake, respiratory exchange ratio, and ventilation were measured on a treadmill and used to calculate Cr.

RESULTS

Compared with men, women displayed a smaller decrease in maximal strength in KE (-36% vs -27%, respectively, P < 0.01), independent of race distance. In SHORT only, women displayed less peripheral fatigue in PF compared with men (Δ peak twitch: -10% vs -24%, respectively, P < 0.05). Cr increased similarly in men and women.

CONCLUSIONS

Women experience less neuromuscular fatigue than men after both "classic" and "extreme" prolonged running exercises but this does not impact the degradation of the energy Cr.

Effect of race distance on performance fatigability in male trail and ultra-trail runners

The etiology of changes in lower-limb neuromuscular function, especially to the central nervous system, may be affected by exercise duration. Direct evidence is lacking as few studies have directly compared different race distances. This study aimed to investigate the etiology of deficits in neuromuscular function following short versus long trail-running races. Thirty-two male trail runners completed one of five trail-running races as LONG (>100 km) or SHORT (<60 km). Pre- and post-race, maximal voluntary contraction (MVC) torque and evoked responses to electrical nerve stimulation during MVCs and at rest were used to assess voluntary activation and muscle contractile properties of knee-extensor (KE) and plantar-flexor (PF) muscles. Transcranial magnetic stimulation (TMS) was used to assess evoked responses and corticospinal excitability in maximal and submaximal KE contractions. Race distance correlated with KE MVC (ρ = -0.556) and twitch (ρ = -0.521) torque decreases (p ≤ .003). KE twitch torque decreased more in LONG (-28 ± 14%) than SHORT (-14 ± 10%, p = .005); however, KE MVC time × distance interaction was not significant (p = .073). No differences between LONG and SHORT for PF MVC or twitch torque were observed. Maximal voluntary activation decreased similarly in LONG and SHORT in both muscle groups (p ≥ .637). TMS-elicited silent period decreased in LONG (p = .021) but not SHORT (p = .912). Greater muscle contractile property impairment in longer races, not central perturbations, contributed to the correlation between KE MVC loss and race distance. Conversely, PF fatigability was unaffected by race distance.

Influence of wide-pulse neuromuscular electrical stimulation frequency and superimposed tendon vibration on occurrence and magnitude of extra torque

Low-frequency and high-frequency wide-pulse neuromuscular electrical stimulation (NMES) can generate extra torque (ET) via afferent pathways. Superimposing tendon vibration (TV) to NMES can increase the activation of these afferent pathways and favor ET generation. Knowledge of the characteristics of ET is essential to implement these stimulation paradigms in clinical practice. Thus, we aimed to investigate the effects of frequency and TV superimposition on the occurrence and magnitude of ET in response to wide-pulse NMES. NMES-induced isometric plantar flexion torque was recorded in 30 healthy individuals who performed five NMES protocols: wide-pulse low-frequency (1 ms; 20 Hz; WPLF) and wide-pulse high-frequency (1 ms; 100 Hz; WPHF) without and with superimposed TV (1 mm; 100 Hz) and conventional NMES (50 µs; 20 Hz; reference protocol). Each NMES protocol consisted of three 20-s trains interspersed by 90 s of rest, with NMES intensity being adjusted to reach 10% of maximal voluntary contraction. The ET occurrence was similar for WPLF and WPHF (P = 0.822). In the responders, the ET magnitude was greater for WPHF than WPLF (P < 0.001). There was no effect of superimposed TV on ET characteristics. This study reported an effect of NMES frequency on ET magnitude, whereas TV superimposition did not affect this parameter. In the context of our experimental design decisions, the present findings question the clinical use of wide-pulse NMES and its combination with superimposed TV. Yet, further research is needed to maximize force production through the occurrence and magnitude of ET.NEW & NOTEWORTHY This study is the first to assess the effect of stimulation frequency and superimposed tendon vibration on extra torque characteristics generated by wide-pulse neuromuscular electrical stimulation. The percentage of subjects showing extra torque (i.e., considered as responders) was similar for low-frequency and high-frequency wide-pulse neuromuscular electrical stimulation. In the responders, the extra torque was greater for high-frequency than for low-frequency wide-pulse neuromuscular electrical stimulation. The superimposition of tendon vibration had no effect on extra torque occurrence or magnitude.

Reductions in motoneuron excitability during sustained isometric contractions are dependent on stimulus and contraction intensity

Cervicomedullary stimulation provides a means of assessing motoneuron excitability. Previous studies demonstrated that during low-intensity sustained contractions, small cervicomedullary evoked potentials (CMEPs) conditioned using transcranial magnetic stimulation (TMS-CMEPs) are reduced, whereas large TMS-CMEPs are less affected. As small TMS-CMEPs recruit motoneurons most active during low-intensity contractions whereas large TMS-CMEPs recruit a high proportion of motoneurons inactive during the task, these results suggest that reductions in motoneuron excitability could be dependent on repetitive activation. To further test this hypothesis, this study assessed changes in small and large TMS-CMEPs across low- and high-intensity contractions. Twelve participants performed a sustained isometric contraction of the elbow flexor for 4.5 min at the electromyography (EMG) level associated with 20% maximal voluntary contraction force (MVC; low intensity) and 70% MVC (high intensity). Small and large TMS-CMEPs with amplitudes of ∼15% and ∼50% M_max at baseline, respectively, were delivered every minute throughout the tasks. Recovery measures were taken at 1-, 2.5- and 4-min postexercise. During the low-intensity trial, small TMS-CMEPs were reduced at 2-4 min (P ≤ 0.049) by up to -10% M_max, whereas large TMS-CMEPs remained unchanged (P ≥ 0.16). During the high-intensity trial, small and large TMS-CMEPs were reduced at all time points (P < 0.01) by up to -14% and -33% M_max, respectively, and remained below baseline during all recovery measures (P ≤ 0.02). TMS-CMEPs were unchanged relative to baseline during recovery following the low-intensity trial (P ≥ 0.24). These results provide novel insight into motoneuron excitability during and following sustained contractions at different intensities and suggest that contraction-induced reductions in motoneuron excitability depend on repetitive activation.NEW & NOTEWORTHY This study measured motoneuron excitability using cervicomedullary evoked potentials conditioned using transcranial magnetic stimulation (TMS-CMEPs) of both small and large amplitudes during sustained low- and high-intensity contractions of the elbow flexors. During the low-intensity task, only the small TMS-CMEP was reduced. During the high-intensity task, both small and large TMS-CMEPs were substantially reduced. These results indicate that repetitively active motoneurons are specifically reduced in excitability compared with less active motoneurons in the same pool.

Fatigue-induced changes in short-interval intracortical inhibition and the silent period with stimulus intensities evoking maximal versus submaximal responses

During fatiguing exercise, previous studies have employed transcranial magnetic stimulation (TMS) paradigms eliciting either maximal or submaximal short-interval intracortical inhibition (SICI) and silent period (SP) durations. However, the effect of using either approach on the change in these variables with fatigue is unknown. This study examined the effects of using conditioning stimulus (CS, experiment A) and single-pulse TMS intensities (experiment B) that elicit maximal and submaximal SICI and SP duration (MaxSICI vs. SubmaxSICI in experiment A, MaxSP vs. SubmaxSP in experiment B) on the change in these measures with fatigue. In both experiments, participants performed a 10-min sustained isometric knee-extension contraction at a constant level of EMG, with measurements taken with maximal and submaximal intensities at baseline and every 2.5 min throughout the task. Immediately after the 10-min contraction (i.e., without recovery), responses were also measured at the same absolute force level as at baseline. In experiment A, no change in SICI was observed with either CS intensity throughout the EMG task (P > 0.05). However, an 18% decrease in SICI (i.e., less inhibition) was observed at the same absolute force only with the MaxSICI CS intensity (P < 0.01), with no change in SubmaxSICI (P = 0.72). In experiment B, the magnitude of increase in SP with fatigue was similar for both stimulus intensities (stimulus × time interaction: P = 0.44). These results suggest that CS intensities eliciting maximum SICI are more sensitive in detecting fatigue-induced reductions in SICI, whereas increases in SP are detectable with TMS intensities evoking maximal or submaximal SPs.NEW & NOTEWORTHY This study compared the change in silent period (SP) and short-interval intracortical inhibition (SICI) with conditioning stimulus and single-pulse transcranial magnetic stimulation (TMS) intensities (for SICI and SP, respectively) eliciting maximal and submaximal SICI and SP during fatiguing exercise. The results showed that changes in SICI were only detectable with intensities evoking maximal responses, with no difference between intensities for SP. These findings highlight the importance of maximizing SICI with appropriate intensities before measuring SICI during fatiguing exercise.

Effects of graduated compression stockings, local vibration and their combination on popliteal venous blood velocity

Objectives

The purpose of this pilot study was to examine and compare the effects of graduated compression stockings, local vibration, and combined graduated compression stockings and local vibration on popliteal venous blood velocity.

Method

Twenty-four healthy subjects received four 15 min interventions (control, graduated compression stockings alone, local vibration alone, and combined graduated compression stockings and local vibration), while resting inactive in the prone position. Popliteal vein blood velocity was investigated before (PRE) and at the end (POST) of each intervention using Doppler ultrasound.

Results

At POST, peak velocity was reported to be 26.3 ± 53.5% ( p <  0.05) greater for local vibration than control (CONT). Peak velocity was 46.2 ± 54.6% ( p <  0.001) and 21.1 ± 37.6% ( p <  0.01) higher for graduated compression stockings than CONT and local vibration, respectively. Graduated compression stockings + local vibration presented 64.1 ± 58.0% ( p <  0.001), 38.4 ± 52.4% ( p <  0.001) and 15.0 ± 31.6% ( p <  0.05) greater values than CONT, local vibration and graduated compression stockings, respectively.

Conclusions

This study demonstrated an increase in popliteal venous blood velocity after graduated compression stockings and local vibration application. Their combination provided the greatest effects.

Rate of force development and rapid muscle activation characteristics of knee extensors in very old men

The age-related decrease in neuromuscular performance is usually accentuated in very old age (>80 yr) as evidenced by a marked reduction in maximal force production. However, little is known about the ability to rapidly produce force, which limits daily activities and increase the risk of falling. We aimed to assess rapid force production characteristics and rate of muscle activation of the knee extensors in 15 very old (82 ± 1 yr) vs 12 young (24 ± 4 yr) men. Maximal force (F_max) and maximal rate of force development (RFD_max) were determined during separated specific isometric contractions. EMG from the vastus lateralis was analyzed to assess the rate of EMG rise (RER). Finally, RFD and RER were examined at time intervals of 0-50, 50-100, 100-200, 0-200 ms and 0-30, 0-50, 0-75 ms, respectively. We reported lower F_max (414 ± 91 N vs. 661 ± 139 N) and absolute RFD_max (8720 ± 2056 N*s^-1vs. 5700 ± 2474 N*s^-1) in the very old men compared to young men (P < 0.01). When normalized to F_max, RFD_max was similar between groups. Normalized RFD at 0-50 and 0-200 ms were lower (-34% and - 46%, P = 0.04) for the very old men, while no difference was observed at 50-100 ms and 100-200 ms. RER values were higher (~346%, P < 0.01) for the young men at every time interval. These data suggest that the decline in RFD_max is associated with the decrease in F_max. Impairments in RFD were accentuated in the first phase of the contraction, which has been associated in the literature with impairments in neural factors associated with aging.