Abstract We investigated the reliability of a test assessing quadriceps strength, endurance and fatigability in a single session. We used femoral nerve magnetic stimulation (FMNS) to distinguish ...central and peripheral factors of neuromuscular fatigue. We used a progressive incremental loading with multiple assessments to limit the influence of subject’s cooperation and motivation. Twenty healthy subjects (10 men and 10 women) performed the test on two different days. Maximal voluntary strength and evoked quadriceps responses via FMNS were measured before, after each set of 10 submaximal isometric contractions (5-s on/5-s off; starting at 10% of maximal voluntary strength with 10% increments), immediately and 30 min after task failure. The test induced progressive peripheral (41 ± 13% reduction in single twitch at task failure) and central fatigue (3 ± 7% reduction in voluntary activation at task failure). Good inter-day reliability was found for the total number of submaximal contractions achieved (i.e. endurance index: ICC = 0.83), for reductions in maximal voluntary strength (ICC > 0.81) and evoked muscular responses (i.e. fatigue index: ICC > 0.85). Significant sex-differences were also detected. This test shows good reliability for strength, endurance and fatigability assessments. Further studies should be conducted to evaluate its feasibility and reliability in patients.
Key points
Twitch transdiaphragmatic pressure elicited by cervical magnetic stimulation of the phrenic nerves is a fully non‐volitional method for assessing diaphragm contractility in humans, yet it ...requires invasive procedures such as oesophageal and gastric catheter balloons.
Ultrafast ultrasound enables a very high frame rate allowing the capture of transient events, such as muscle contraction elicited by nerve stimulation (twitch). Whether indices derived from ultrafast ultrasound can be used as an alternative to the invasive measurement of twitch transdiaphragmatic pressure is unknown.
Our findings demonstrate that maximal diaphragm tissue velocity assessed using ultrafast ultrasound following cervical magnetic stimulation is reliable, sensitive to change in cervical magnetic stimulation intensity, and correlates to twitch transdiaphragmatic pressure.
This approach provides a novel fully non‐invasive and non‐volitional tool for the assessment of diaphragm contractility in humans.
Measuring twitch transdiaphragmatic pressure (Pdi,tw) elicited by cervical magnetic stimulation (CMS) is considered as a reference method for the standardized evaluation of diaphragm function. Yet, the measurement of Pdi requires invasive oesophageal and gastric catheter‐balloons. Ultrafast ultrasound is a non‐invasive imaging technique enabling frame rates high enough to capture transient events such as evoked muscle contractions. This study investigated relationships between indices derived from ultrafast ultrasound and Pdi,tw, and how these indices might be used to estimate Pdi,tw. CMS was performed in 13 healthy volunteers from 30% to 100% of maximal stimulator intensity in units of 10% in a randomized order. Pdi,tw was measured and the right hemidiaphragm was imaged using a custom ultrafast ultrasound sequence with 1 kHz framerate. Maximal diaphragm axial velocity (Vdi,max) and diaphragm thickening fraction (TFdi,tw) were computed. Intra‐session reliability was assessed. Repeated‐measures correlation (R) and Spearman correlation coefficients (ρ) were used to assess relationships between variables. Intra‐session reliability was strong for Pdi,tw and Vdi,max and moderate for TFdi,tw. Vdi,max correlated with Pdi,tw in all subjects (0.64 < ρ < 1.00, R = 0.75; all P < 0.05). TFdi,tw correlated with Pdi,tw in eight subjects only (0.85 < ρ < 0.93, R = 0.69; all P < 0.05). Coupling ultrafast ultrasound and CMS shows promise for the non‐invasive and fully non‐volitional assessment of diaphragm contractility. This approach opens up the prospect of both diagnosis and follow‐up of diaphragm contractility in clinical populations.
Key points
Twitch transdiaphragmatic pressure elicited by cervical magnetic stimulation of the phrenic nerves is a fully non‐volitional method for assessing diaphragm contractility in humans, yet it requires invasive procedures such as oesophageal and gastric catheter balloons.
Ultrafast ultrasound enables a very high frame rate allowing the capture of transient events, such as muscle contraction elicited by nerve stimulation (twitch). Whether indices derived from ultrafast ultrasound can be used as an alternative to the invasive measurement of twitch transdiaphragmatic pressure is unknown.
Our findings demonstrate that maximal diaphragm tissue velocity assessed using ultrafast ultrasound following cervical magnetic stimulation is reliable, sensitive to change in cervical magnetic stimulation intensity, and correlates to twitch transdiaphragmatic pressure.
This approach provides a novel fully non‐invasive and non‐volitional tool for the assessment of diaphragm contractility in humans.
Keywords: cervical magnetic stimulation; contractility; diaphragm; phrenic nerves; skeletal muscle; ultrafast ultrasound imaging Article Note: Edited by: Scott Powers & Ken O'Halloran Linked ...articles: This is a reply to a Letter to the Editor by Beltrami. To read the Letter to the Editor, visit Poulard et al. To read the article, visit Jean-Luc Gennisson and Damien Bachansson contributed equally to this work. Byline: Thomas Poulard, Martin Dres, Marie-Cecile Nierat, Isabelle Rivals, Jean-Yves Hogrel, Thomas Similowski, Jean-Luc Gennisson, Damien Bachasson
Objective
To assess quadriceps strength and fatigability by using femoral nerve magnetic stimulation (FNMS) and their relationship to exercise capacity in patients with fibromyalgia syndrome (FMS) ...and healthy controls.
Methods
Twenty‐two women (11 with FMS, 11 controls) performed a maximal incremental cycling test and a quadriceps fatigue test on 2 separate visits. For quadriceps assessment, we used FNMS during and after maximum voluntary contraction (MVC) to evaluate central and peripheral factors of neuromuscular fatigue. Subjects performed sets of 10 intermittent (5 seconds on/5 seconds off) isometric contractions starting at 10% MVC, in 10% MVC increments from one set to another until exhaustion. Neuromuscular fatigue was assessed with FNMS after each set.
Results
FMS patients had reduced initial MVC compared to controls (mean ± SD 102 ± 18 versus 120 ± 24 Nm; P < 0.05) without significant impairment of voluntary activation (mean ± SD 93.5% ± 3.0% versus 93.1% ± 3.4%; P = 0.74). During the fatigue task, FMS patients exhibited a greater fall in evoked muscular responses (mean ± SD −26% ± 6% versus −16% ± 8% at set 50% MVC; P < 0.05), but not in MVC (mean ± SD −24% ± 7% versus −19% ± 4% at set 50% MVC; P = 0.12). During the cycling test, FMS patients had lowered maximal exercise capacity and an enhanced rate of perceived exertion (RPE) compared to controls. The percent reduction in evoked muscular responses during the quadriceps fatigue test correlated with maximum oxygen consumption (r = 0.56, P < 0.05) and RPE at submaximal intensity (r = 0.84, P < 0.05) during cycling.
Conclusion
Greater impairment in muscle contractility is associated with enhanced perception of exertion and reduced maximal exercise capacity in FMS patients. Neuromuscular impairments should be considered as an important factor underlying functional limitations in FMS patients.
Abstract Neuromuscular function can change under different conditions such as ageing, training/detraining, long-term spaceflight, environmental conditions ( e.g. hypoxia, hyperthermia), disease, ...therapy/retraining programs and also with the appearance of fatigue. Neuromuscular fatigue can be defined as any decrease in maximal voluntary strength or power. There is no standardized method to induce fatigue and various protocols involving different contraction patterns (such as sustained or intermittent submaximal isometric or dynamic contractions on isokinetic or custom chairs) have been used. Probably due to lack of motivation/cooperation, results of fatigue resistance protocols are more variable in patients than in healthy subjects. Magnetic and electrical stimulation techniques allow non-invasive assessment of central and peripheral origins of fatigue. They also allow investigation of different types of muscle fatigue when combining various types of stimulation with force/surface EMG measurements. Since maximal electrical stimuli may be uncomfortable or even sometimes painful, several alternative methods have been recently proposed: submaximal muscle stimulation, low/high-frequency paired pulses instead of tetanic stimuli and the use of magnetic stimulation at the peripheral level.
Muscle weakness and fatigability, the prominent symptoms of autoimmune myasthenia gravis (MG), negatively impact daily function and quality of life (QoL). It is currently unclear as to what extent ...symptoms limit activity and whether physical activity (PA) behaviours are associated with reduced QoL.
This study aimed to describe habitual PA patterns and explore relationships between PA metrics, clinical MG characteristics, and health-related QoL (HRQoL).
PA data from a tri-axial trunk accelerometer worn for seven days, was collected from females with generalized, stable MG and compared to control subjects. MG-specific evaluations, the six-minute walk test and knee extension strength were assessed in individuals with MG (IwMG). Mann-Whitney tests were used to study between-group differences. Spearman rank correlation coefficient was performed to explore relationships between variables.
Thirty-three IwMG (mean (SD) age 45 (11) years) and 66 control subjects were included. IwMG perform less vigorous-intensity PA than control subjects (p = 0.001), spend more time sedentary (p = 0.02) and engage in less and shorter durations of moderate-vigorous-intensity PA (MVPA). For IwMG, habitual PA correlated positively with 6 min walking distance (rho = 0.387, p = 0.029) and negatively with body mass index (rho = -0.407, p = 0.019). We did not find any association between PA or sedentary behaviour and; HRQoL, symptom severity nor lower limb strength.
Individuals with stable MG perform less PA, at lower intensities, and are more inactive than control individuals. Further research is warranted to understand factors influencing PA patterns in MG and whether interventions could be successful in increasing PA quantity and intensity in IwMG.
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