Sustained Maximal Voluntary Contraction Research Articles

Effects of Local Heating and Whole-Body Hyperthermia on Neuromuscular and Cognitive Function in Young and Old Healthy Adults

Background and objectives: Aging population is growing fast in European Union and worldwide (Shimizu et al., 2020). A progressive decline in neuromuscular function (Lexell et al., 1983), structural changes in the brain ( Smith et al., 2010; Zahra et al., 2019)aged 30 to 99 years, were studied with MRI. Age was related to estimated volumes of: gray matter, white matter, and CSF of the cerebrum and cerebellum; gray matter, white matter, white matter abnormality, and CSF within each cerebral lobe; and gray matter of eight subcortical structures. The results were: 1, and inefficiencies in thermoregulatory regulation (Blatteis, 2012; Yamashiro et al., 2020) were found in the old population. We conducted three experiments to investigate the effects of short-term and long-term passive heating on motor performance, as well as the impact of whole-body passive heating on cognitive functioning in both healthy older and young adults. Methods: In the first study, weight (kg), body fat (%), height (cm), body mass index (BMI), skinfold thickness (mm), and the mean subcutaneous fat thickness were calculated (McArdle et al., 1984). Ankle muscle torque production and contractile properties were determined by isometric torque of the ankle plantar flexion and the isokinetic (dynamic) torque of the ankle plantar flexion/dorsiflexion muscles using an isokinetic dynamometer (System 4; Biodex Medical Systems, Shirley, NY, USA). In the second study, body surface area, heart rate, muscle temperature, and thermal sensation were measured. Prolactin, interleukin-6, dopamine and cortisol concentrations were obtained via venous blood samples. The isometric torque of ankle plantar flexion muscles was assessed as the first study. In the third study, body weight, sweating rate, rectal temperature, heart rate, physiological strain index (PSI), thermal sensations were investigated. A programmed cognitive test to assess cognitive functioning (Brazaitis et al., 2015). Results: In the first study, for the older adults (vs. younger adults), the application of local heating (vs. control trial) was accompanied by a significant increase in maximal voluntary peak torque, rate of torque development, and isokinetic peak torque of plantar flexion/dorsiflexion muscle contraction. In the second study, older males demonstrated greater neuromuscular fatigability resistance and faster maximal voluntary contraction (MVC) torque recovery after a 2-min sustained isometric MVC task under thermoneutral and severe hyperthermic conditions. In the third study, PSI was lower and cortisol concentration was greater after whole-body heating in the older group compared with the younger group. Surprisingly, hyperthermia improved cognitive flexibility only in old adults, whereas short-term and visual recognition memories were maintained in both age groups. Conclusions: In the first study, the spinal and supraspinal reflex excitability of older adults increased during local knee-heating application. The improved motor drive transmission observed in older adults was accompanied by increased voluntarily induced torque production of the ankle muscles during isometric/isokinetic contractions. In the second study, neuromuscular performance during fatigue-provoking sustained isometric exercise under severe whole body hyperthermia conditions appears to decline in both age groups, but a lower relative decline in torque production for older males may relate to lower psychological and thermophysiological strain along with a diminished dopamine response and prolactin release. In the third study, A ≈ 2.5 ◦C increase in rectal temperature can improve executive function in old adults, and this increase parallels the increased cortisol concentration and the lower thermophysiological strain under severe whole-body hyperthermia conditions.

Skeletal muscle fiber type and TMS-induced muscle relaxation in unfatigued and fatigued knee-extensor muscles.

The force drop after transcranial magnetic stimulation (TMS) delivered to the motor cortex during voluntary muscle contractions could inform about muscle relaxation properties. Because of the physiological relation between skeletal muscle fiber-type distribution and size and muscle relaxation, TMS could be a noninvasive index of muscle relaxation in humans. By combining a noninvasive technique to record muscle relaxation in vivo (TMS) with the gold standard technique for muscle tissue sampling (muscle biopsy), we investigated the relation between TMS-induced muscle relaxation in unfatigued and fatigued states, and muscle fiber-type distribution and size. Sixteen participants (7F/9M) volunteered to participate. Maximal knee-extensor voluntary isometric contractions were performed with TMS before and after a 2-min sustained maximal voluntary isometric contraction. Vastus lateralis muscle tissue was obtained separately from the participants' dominant limb. Fiber type I distribution and relative cross-sectional area of fiber type I correlated with TMS-induced muscle relaxation at baseline (r = 0.67, adjusted P = 0.01; r = 0.74, adjusted P = 0.004, respectively) and normalized TMS-induced muscle relaxation as a percentage of baseline (r = 0.50, adjusted P = 0.049; r = 0.56, adjusted P = 0.031, respectively). The variance in the normalized peak relaxation rate at baseline (59.8%, P < 0.001) and in the fatigue resistance (23.0%, P = 0.035) were explained by the relative cross-sectional area of fiber type I to total fiber area. Fiber type I proportional area influences TMS-induced muscle relaxation, suggesting TMS as an alternative method to noninvasively inform about skeletal muscle relaxation properties.NEW & NOTEWORTHY Transcranial magnetic stimulation (TMS)-induced muscle relaxation reflects intrinsic muscle contractile properties by interrupting the drive from the central nervous system during voluntary muscle contractions. We showed that fiber type I proportional area influences the TMS-induced muscle relaxation, suggesting that TMS could be used for the noninvasive estimation of muscle relaxation in unfatigued and fatigued human muscles when the feasibility of more direct method to study relaxation properties (i.e., muscle biopsy) is restricted.

Measurements of in vivo skeletal muscle oxidative capacity are lower following sustained isometric compared with dynamic contractions.

Human skeletal muscle oxidative capacity can be quantified non-invasively using 31-phosphorus magnetic resonance spectroscopy (31P-MRS) to measure the rate constant of phosphocreatine (PCr) recovery (kPCr) following contractions. In the quadricep muscles, several studies have quantified kPCr following 24-30s of sustained maximal voluntary isometric contraction (MVIC). This approach has the advantage of simplicity but is potentially problematic because sustained MVICs inhibit perfusion, which may limit muscle oxygen availability or increase the intracellular metabolic perturbation, and thus affect kPCr. Alternatively, dynamic contractions allow reperfusion between contractions, which may avoid limitations in oxygen delivery. To determine whether dynamic contraction protocols elicit greater kPCr than sustained MVIC protocols, we used a cross-sectional design to compare quadriceps kPCr in 22 young and 11 older healthy adults following 24s of maximal voluntary: (1) sustained MVIC and (2) dynamic (MVDC; 120°·s-1, 1 every 2s) contractions. Muscle kPCr was ∼20% lower following the MVIC protocol compared with the MVDC protocol (p≤0.001), though this was less evident in older adults (p=0.073). Changes in skeletal muscle pH (p≤0.001) and PME accumulation (p≤0.001) were greater following the sustained MVIC protocol, and pH (p≤0.001) and PME (p≤0.001) recovery were slower. These results demonstrate that (i) a brief, sustained MVIC yields a lower value for skeletal muscle oxidative capacity than an MVDC protocol of similar duration and (ii) this difference may not be consistent across populations (e.g., young vs. old). Thus, the potential effect of contraction protocol on comparisons of kPCr in different study groups requires careful consideration in the future.

Voluntary muscle activation in people with Multiple Sclerosis is reduced across a wide range of forces following maximal effort fatiguing contractions.

Although Multiple Sclerosis (MS) is frequently associated with motor impairment, little is known about how muscle activation is affected with MS. The aim of this study was to use transcranial magnetic stimulation (TMS) and motor nerve stimulation to investigate voluntary muscle activation in people with MS across a range of contraction forces. Ten people with MS (39 ± 7 years) and 10 healthy controls (40 ± 5 years) performed elbow flexions at target contraction forces of 25%, 50%, 75%, 90%, and 100% maximal voluntary contraction (MVC) while electromyography (EMG) of the biceps brachii was recorded. Sustained elbow flexion MVCs were then performed until force declined to 60% of baseline MVC, where the target contraction forces were again examined but after the sustained MVC. Following the sustained MVC there was a reduction in biceps EMG amplitude (P < 0.01) and motor cortical voluntary activation (P < 0.01) for the MS group across all contraction intensities. There was also an increase in the rate of torque development for motor nerve resting twitches in the MS group following the sustained MVC (P = 0.03). Despite the MS group reporting higher Fatigue Severity Scale scores (P < 0.01), disease duration was a better predictor of muscle activation for the MS group (r = -0.757, P = 0.01). These findings indicate that voluntary muscle activation is compromised in people with MS following maximal effort contractions, which may be associated with disease duration rather than self-reports of fatigue.

Comparison between conventional and neuronavigated strategies to assess corticospinal responsiveness in unfatigued and fatigued knee-extensor muscles

In studying neuromuscular fatigability, researchers commonly use functional criteria to position and hold the transcranial magnetic stimulation (TMS) coil during testing sessions. This could influence the magnitude of corticospinal excitability and inhibition responses due to imprecise and unsteady positions of the coil. To reduce coil position and orientation variability, neuronavigated TMS (nTMS) could be used. We evaluated the accuracy of nTMS and a standardized function-guided procedure for maintaining TMS coil position both in unfatigued and fatigued knee extensors. Eighteen participants (10F/8M) volunteered in two identical and randomized sessions. Maximal and submaximal neuromuscular evaluations were performed with TMS three times before (PRE_1) and three times after (PRE_2) a 2 min resting session and one time immediately after (POST) a 2-min sustained maximal voluntary isometric contraction (MVIC). The located “hotspot” [the location that evoked the largest motor-evoked potential (MEP) responses in the rectus femoris] was maintained either with or without nTMS. MEP, silent period (SP) and the distance between the “hotspot” and the actual coil position were recorded. A time × contraction intensity × testing session × muscle interaction was not observed for MEP, SP, and distance. Bland-Altman plots presented adequate agreements for MEP and SP. Spatial accuracy of TMS coil position over the motor cortex did not influence corticospinal excitability and inhibition in unfatigued and fatigued knee extensors. The variability in MEP and SP responses may be due to spontaneous fluctuations in corticospinal excitability and inhibition, and it is not altered by the spatial stability of the stimulation point.

Comparison between Two Different Handgrip Systems and Protocols on Force Reduction in Handgrip Assessment

Introduction: Fatigue resistance (FR) can be assessed as the time during which grip strength (GS) drops to 50% of its maximum during a sustained maximal voluntary contraction. For the first time, we compared force-time characteristics during FR test between two different handgrip systems and investigated age- and clinical-related differences in order to verify if a briefer test protocol (i.e., until 75%) could be sufficiently informative. Methods: A cohort of young healthy controls (Y, <30 y, 24 ± 3 y, 54% women), middle-aged (MA, 30–65 y, 47 ± 11 y, 54% women), and older (OLD, >65 y, 77 ± 7 y, 50% women) community-dwelling persons, and hospitalized geriatric patients (HOSP, 84 ± 5 y, 50% women) performed the FR test. For this purpose, an adapted vigorimeter (original rubber bulb of the Martin Vigorimeter connected to a Unik 5000 pressure gauge) here defined as “pneumatic handgrip system” (Pneu) and Dynamometer G200 system (original Jamar Dynamometer handle with an in-build strength gauge) here defined as “hydraulic handgrip system” (Hydr) were used. Force-time curves were analysed from 100% to 75% and from 75% to 50% of the initial maximal GS during the FR test. The area under the curve (GW) was calculated by integrating the actual GS at each time interval (i.e., 1/5,000 s) and corrected for body weight (GW/_{body weight}). Results: For both systems, we found fair associations between FR_100–50 and FR_100–75 (Pneu mean difference = 50.1 s [95% CI: 47.9–52.4], r² = 0.48; Hydr mean difference = 28.4 s [95% CI: 27.0–29.7], r² = 0.52, all p < 0.001) and also moderate associations between GW_{(100–50)/body weight} and GW_{(100–75)/body weight} (Pneu mean difference = 32.1 kPa*s/kg [95% CI: 30.6–33.6], r² = 0.72; Hydr mean difference = 8.1 kg*s/kg [95% CI: 7.7–8.6], r² = 0.68, all p < 0.001). Between MA and OLD, we found a significant age-related difference in the GW results in the first 25% strength decay for Pneu (10.2 ± 0.6 kPa*s/kg against 7.1 ± 1.2 kPa*s/kg, respectively). Conclusion: The brief test protocol is valid. Differences within the first 25% strength decay in GW between OLD and HOSP were identified when using Pneu but not when using Hydr. Therefore, a brief FR test protocol using a continuous registration of the strength decay seems to be sufficiently informative in a clinical setting to appraise muscle fatigability, however, only when using a Pneu system.

MP37-18 A PROSPECTIVE COHORT STUDY DEMONSTRATING EXERCISE EFFECTS FROM HOME BASED PELVIC FLOOR MUSCLE TRAINING TO REHABILITATE NEUROGENIC LOWER URINARY TRACT DYSFUNCTION; 3D REGIONAL EFFECTS

You have accessJournal of UrologyCME1 Apr 2023MP37-18 A PROSPECTIVE COHORT STUDY DEMONSTRATING EXERCISE EFFECTS FROM HOME BASED PELVIC FLOOR MUSCLE TRAINING TO REHABILITATE NEUROGENIC LOWER URINARY TRACT DYSFUNCTION; 3D REGIONAL EFFECTS Lynn Stothers, Andrew Macnab, Naser Hakimi, W. N. J. M. Colier, M. Maresse, and P. Pourabbassi Lynn StothersLynn Stothers More articles by this author , Andrew MacnabAndrew Macnab More articles by this author , Naser HakimiNaser Hakimi More articles by this author , W. N. J. M. ColierW. N. J. M. Colier More articles by this author , M. MaresseM. Maresse More articles by this author , and P. PourabbassiP. Pourabbassi More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000003275.18AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Women with neurogenic lower urinary tract dysfunction (NLUTD) rely on pelvic floor muscle rehabilitation therapy (PFMT) to aid continence. However, in NLUTD including spinal cord injury (SCI) PFM function is known to be affected regionally/asymmetrically which is not detected through exam or manometry. Objective: Report clinical translation of a optical PFM system, patient informed design to provide a 3D measures of PFM contractions quantifiable by reoxygenation recovery following sustained maximal voluntary contractions (SMVC) employed in PFMT. METHODS: An optical transvaginal interface was engineered using a circumferential grid of 6 light emitting diodes (LED’s) (wavelengths 750 & 860nm) & 4 photodiode detectors. Engineering design met preferences for size, shape, weight & ergometric features from a prior end user survey (Figure 1) Sampling at 50Hz, changes in oxy and deoxy-hemoglobin concentration (O2Hb/HHb) during PFM contractions monitored in real time, multiple point, from which HbDiff (O2Hb-HHb) is derived. All completed pre/post Qualiveen, were evaluated via NIRS during a standardized sequence of maximum & sustained PFM contractions, engaged in 12 weeks home based PFMT then repeat optical-derived measures of reoxygenation recovery. RESULTS: N=14 women (5 controls 7 NLUTD) 25–82 yrs. Baseline Qualiveen scores range: 0 (controls)-0.7 (NLUTD). Figure 1: output showing post PFMT composite graphics with NIRS data from channels monitoring the right & left sides of both the anterior & posterior segments of the PFM during 3 SMVC’s. All subjects were monitored successfully pre/post PFMT demonstrating 3D detailed functional ability of small segments of the pelvic floor & documenting effects of training. CONCLUSIONS: Optical detection of a validated quantifiable parameter of muscle reoxygenation in the PFM is feasible using this transvaginal optical interface designed based on women with NLUTD end user feedback. The multipoint design allows small regional variations in PFM functionality to be quantified & improvements from PFMT training effects to be measured in NLUTD/SCI to enhance rehabilitation of women living with NLUTD known to impact negatively on quality of life. Source of Funding: Craig H Neilsen Foundation © 2023 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 209Issue Supplement 4April 2023Page: e521 Advertisement Copyright & Permissions© 2023 by American Urological Association Education and Research, Inc.MetricsAuthor Information Lynn Stothers More articles by this author Andrew Macnab More articles by this author Naser Hakimi More articles by this author W. N. J. M. Colier More articles by this author M. Maresse More articles by this author P. Pourabbassi More articles by this author Expand All Advertisement PDF downloadLoading ...

Shouting strengthens voluntary force during sustained maximal effort through enhancement of motor system state via motor commands

Previous research indicates that shouting during momentary maximal exertion effort potentiates the maximal voluntary force through the potentiation of motor cortical excitability. However, the muscular force-enhancing effects of shouting on sustained maximal force production remain unclear. We investigated the effect of shouting on the motor system state by examining motor evoked potentials in response to transcranial magnetic stimulation applied over the hand area of the contralateral primary motor cortex (M1) during sustained maximal voluntary contraction, and by assessing handgrip maximal voluntary force. We observed that shouting significantly increased handgrip maximal voluntary force and reduced the silent period. Our results indicate that shouting increased handgrip voluntary force during sustained maximal exertion effort through the reduced silent period. This is the first objective evidence that the muscular force of shouting during maximal force exertion is associated with the potentiation of motor system activity produced by the additional drive of shouting operating on the motor system (i.e., shouting-induced excitatory input to M1).

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.

Modulation of neuromuscular excitability in response to acute noxious heat exposure has no additional effects on central and peripheral fatigability.

Background: Whole-body hyperthermia (WBH) has an adverse effect on the nervous system and neurophysiological performance. In the present study, we examined whether short-duration whole-body immersion in 45°C water (HWI-45°C), which produces a strong neural and temperature flux without inducing WBH, can increase or impair neurophysiological performance in humans. Methods: Fifteen men (aged 25 ± 6 years) were enrolled in this study and participated in three experiments: 1) a brief (5-min) immersion of the whole body in 37°C water (WI-37°C); 2) a brief (5-min) HWI-45°C; and 3) a control trial in a thermoneutral condition at an ambient temperature of 24°C and 60% relative humidity. Before and after the immersions, neuromuscular function (electromyographic activity, reflexes, electrically and voluntary induced torque production, voluntary muscle activation level) were tested. To provoke central inhibition, the participants performed a sustained 2-min maximal voluntary contraction (MVC). Results: Thermophysiological strain was greater after HWI-45°C than after WI-37°C. Electrophysiological modulations of motor drive transmission and peripheral modulations of muscle contractility properties in response to HWI-45°C seemed to have little effect on central activation of the exercising muscles and no effect on MVC production. Conclusion: Although exposure to acute noxious heat was effective in evoking neuromuscular excitability, the increases in core temperature (∼0.2°C) and muscle temperature (∼0.6°C) did not induce moderate or severe WBH. These changes did not seem to affect central structures; that is, there were no additional increases in central and/or peripheral fatigue during a sustained 2-min MVC.

Post‐fatigue ability to activate muscle is compromised across a wide range of torques during acute hypoxic exposure

The purpose of this study was to assess how severe acute hypoxia alters the neural mechanisms of muscle activation across a wide range of torque output in a fatigued muscle. Torque and electromyography responses to transcranial and motor nerve stimulation were collected from 10 participants (27 years ± 5 years, 1 female) following repeated performance of a sustained maximal voluntary contraction that reduced torque to 60% of the pre‐fatigue peak torque. Contractions were performed after 2 h of hypoxic exposure and during a sham intervention. For hypoxia, peripheral blood oxygen saturation was titrated to 80% over a 15‐min period and remained at 80% for 2 h. Maximal voluntary torque, electromyography root mean square, voluntary activation and corticospinal excitability (motor evoked potential area) and inhibition (silent period duration) were then assessed at 100%, 90%, 80%, 70%, 50% and 25% of the target force corresponding to the fatigued maximal voluntary contraction. No hypoxia‐related effects were identified for voluntary activation elicited during motor nerve stimulation. However, during measurements elicited at the level of the motor cortex, voluntary activation was reduced at each torque output considered (P = .002, η p 2 = .829). Hypoxia did not impact the correlative linear relationship between cortical voluntary activation and contraction intensity or the correlative curvilinear relationship between motor nerve voluntary activation and contraction intensity. No other hypoxia‐related effects were identified for other neuromuscular variables. Acute severe hypoxia significantly impairs the ability of the motor cortex to voluntarily activate fatigued muscle across a wide range of torque output.

Fatigue in primary Sjögren's syndrome is associated with an objective decline in physical performance, pain and depression.

Fatigue is a major complaint in primary Sjögren's syndrome (pSS). To acquire a better understanding of fatigue in pSS, we investigated objective measures of performance decline (performance fatigability). Furthermore, we evaluated the relationship of self-reported fatigue with performance fatigability and factors modulating perceptions of fatigability (perceived fatigability). Thirty-nine pSS patients and 27 healthy controls were included. To assess performance fatigability, force decline was measured during a sustained (124s) maximal voluntary contraction (MVC) with the index finger abductor muscle, and voluntary muscle activation was indexed using peripheral nerve stimulation. Self-reported fatigue was quantified using the Fatigue Severity Scale (FSS) and Modified Fatigue Impact Scale (MFIS). Pain, depression, and anxiety assessed using questionnaires and inflammatory biomarkers measured in blood were used as factors relating to perceived fatigability. Voluntary muscle activation was reduced in pSS (p=0.030), but force decline during the sustained MVC did not differ between groups. Self-reported fatigue was significantly higher in pSS than in controls (FSS: 4.4 vs. 2.6, p<0.001). Multivariable linear regression showed that both performance fatigability (force decline) and perceived fatigability (pain and depression) were associated with the MFIS physical domain in pSS (total explained variance of 47%). Negative associations with fatigue were observed for two interferon-associated proteins: MxA and CXCL10. This study demonstrates that performance fatigability in pSS was compromised by a reduced capacity of the central nervous system to drive the muscle. Furthermore, self-reported fatigue is a multifactorial symptom associated with both performance fatigability and perceived fatigability in patients with pSS.

Reliability of relaxation properties of knee-extensor muscles induced by transcranial magnetic stimulation

Transcranial magnetic stimulation (TMS)-induced relaxation rate reflects intrinsic muscle contractile properties by interrupting the drive from the central nervous system during voluntary muscle contractions. To determine the appropriateness of knee-extensor muscle relaxation measurements induced by TMS, this study aimed to establish both the within- and between-session reliability before and after a fatiguing exercise bout. Eighteen participants (9 females, 9 males, age 25 ± 2 years, height 171 ± 9 cm, body mass 68.5 ± 13.5 kg) volunteered to participate in two identical sessions approximately 30 days apart. Maximal and submaximal neuromuscular evaluations were performed with TMS six times before (PRE) and at the end (POST) of a 2-min sustained maximal voluntary isometric contraction. Within- and between-session reliability of PRE values were assessed with intraclass correlation coefficient (ICC2,1, relative reliability), repeatability coefficient (absolute reliability), and coefficient of variation (variability). Test-retest reliability of post-exercise muscle relaxation rates was assessed with Bland-Altman plots. For both the absolute and normalized peak relaxation rates and time to peak relaxation, data demonstrated low variability (e.g. coefficient of variation ≤ 7.8%) and high reliability (e.g. ICC2,1 ≥ 0.963). Bland-Altman plots showed low systematic errors. These findings establish the reliability of TMS-induced muscle relaxation rates in unfatigued and fatigued knee-extensor muscles, showing that TMS is a useful technique that researchers can use when investigating changes in muscle relaxation rates both in unfatigued and fatigued knee-extensor muscles.

PD24-04 DETECTION OF PELVIC FLOOR MUSCLE ACTIVITY AND QUANTIFICATION OF OXYGEN KINETICS IN WOMEN WITH SPINAL CORD INJURY AND NEUROGENIC LOWER URINARY TRACT DYSFUNCTION

You have accessJournal of UrologyCME1 May 2022PD24-04 DETECTION OF PELVIC FLOOR MUSCLE ACTIVITY AND QUANTIFICATION OF OXYGEN KINETICS IN WOMEN WITH SPINAL CORD INJURY AND NEUROGENIC LOWER URINARY TRACT DYSFUNCTION Lynn Stothers, and Andrew Macnab Lynn Stothers Lynn Stothers More articles by this author , and Andrew MacnabAndrew Macnab More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000002566.04AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Paralysis and changes in sensation following spinal cord injury (SCI) are a significant barrier to the performance and quantification of pelvic floor muscle (PFM) exercise in women, although international guidelines recommend PFM therapy. Aims: (1) to translate for use in PFM evaluation, a validated optical measure of oxygen kinetics used in sports medicine which uses near infrared (NIR) spectroscopy to quantify the half recovery time of reoxygenation (HbDiff(½RT)) following sustained maximal voluntary muscle contraction (SMVC), and (2) design and test a vaginal interface incorporating NIRS technology specific to the needs of women with compromised PFM function due to SCI. METHODS: The vaginal interface (fig left) incorporates 4 NIRS emitter detector arrays; photons of NIR light (wavelengths 825, 950, 1000 nm) monitor changes in oxygenated and deoxygenated hemoglobin (O2Hb/HHb) at capture rates of 10 Hz during PFM muscle contractions. The study protocol included clinical assessment, bladder diary and Qualiveen symptom scores and perineometry, plus changes in O2Hb/HHb at rest and during PFM rehabilitation exercises. The absolute measure HbDiff(½RT) is derived from the slope of reoxygenation following release of each SMVC. RESULTS: N=15 women aged 25-59 yrs (5 controls, 10 SCI ASIA B, C, D) completed 4 weeks of PFMT; HbDiff(½RT) data sets were compared within individuals and between clinical groups. Repeatability of patterns of recovery were demonstrable within individuals (fig right). CONCLUSIONS: HbDiff(½RT) is a quantifiable absolute measure of skeletal muscle oxygen kinetics; use of the vaginal interface allows individual elements of the PFM to be evaluated; the ability to quantify right and left sided function independently is particularly relevant in women with PFM dysfunction due to partial SCI. Translation of measurement of HbDiff(½RT) to the PFM now allows a validated muscle reoxygenation parameter to be applied in evaluation of PFM dysfunction following SCI in women, and offers a means to quantify clinical training effects from rehabilitation exercise in NLUTD. Source of Funding: Craig Neilsen Foundation © 2022 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 207Issue Supplement 5May 2022Page: e416 Advertisement Copyright & Permissions© 2022 by American Urological Association Education and Research, Inc.MetricsAuthor Information Lynn Stothers More articles by this author Andrew Macnab More articles by this author Expand All Advertisement PDF DownloadLoading ...

Advanced Technology or Manual Skills: Evidence That The Accuracy of Corticospinal Responsiveness Is Not Ameliorated by Neuronavigation

PurposeTranscranial magnetic stimulation (TMS) is a noninvasive technique to assess corticospinal excitability and inhibition. TMS over the motor cortex during a voluntary contraction elicits short‐latency excitatory (motor‐evoked potential, MEP) and inhibitory (silent period, SP) responses in the target muscle. However, the technique for searching and determining the optimal site to elicit MEPs (“hotspot”), an essential component in order to correctly place the TMS coil, is not unanimously standardized. This can be a problem since changes in coil position and/or orientation may influence the magnitude of MEP and SP responses. Usually, the “hotspot” is marked either on a swim cap or on the scalp and the investigator holds the coil manually during the entire testing session. However, the capacity to maintain the coil placement within and between sessions may be limited. To reduce variability in coil position and orientation in space and over time, neuronavigated TMS (nTMS) is used. However, no studies investigated the accuracy of the assessment of corticospinal excitability and inhibition using nTMS versus a traditional manual approach for the maintenance of coil positioning.Methods18 healthy participants (10W/8M) volunteered in two identical and randomized sessions ~30 days apart. Maximal and submaximal neuromuscular evaluations were performed with TMS six times before (PRE), and at the end (POST) of a 2‐min sustained maximal voluntary isometric contraction (MVIC) (100%, 75%, 50% MVIC and 25%isoEMG). The “hotspot” was maintained either with a grid demarcated on the participants’ scalp or with visual feedback provided by nTMS on a computer screen. In both sessions, “hotspot” was considered as the site where the largest MEPs in the rectus femoris were elicited.ResultsThere were not a “hotspot” technique × contraction intensities × time points interactions for both MEP (P = 0.217) and SP (P = 0.627). Bland‐Altman plots display adequate agreements between the difference in the two “hotspot” techniques and the means of the two “hotspot” techniques. The slopes of the resulting regression lines were not significantly different from zero (horizontal to x‐axis) for both MEP (all r ≤ 0.335, all P ≥ 0.162) and SP (all r ≤ 0.382, all P ≥ 0.131), indicating a uniformity of systematic error at all contraction intensities and time points.ConclusionsSpatial stability of the TMS coil position over the motor cortex did not influence corticospinal excitability and inhibition responses in unfatigued and fatigued knee extensors. This is because the variability in MEP and SP responses is due to spontaneous fluctuations in corticospinal and motoneuron excitability and inhibition; and this variability is not affected by spatial accuracy. Therefore, nTMS or a traditional manual approach could be interchangeably use in order to maintain the TMS coil position in the exact “hotspot”.

Establishing Task-Relevant MVC Protocols for Modelling Sustained Isometric Force Variability: A Manual Control Study.

The present study examined how prevalent methods for determining maximal voluntary contraction (MVC) impact the experimentally derived functions of graded force-force variability. Thirty-two young healthy subjects performed continuous isometric force tracking (20 s trials) at 10 target percentages (5–95% MVC) normalized to a conventional discrete-point (n = 16), or sustained (n = 16) MVC calculation. Distinct rates and magnitudes of change were observed for absolute variability (standard deviation (SD), root mean squared error (RMSE)), tracking error (RMSE, constant error (CE)), and complexity (detrended fluctuation analysis (DFA)) (all p < 0.05) of graded force fluctuations between the MVC groups. Differential performance strategies were observed beyond ~65% MVC, with the discrete-point group minimizing their SD at force values below that of the criterion target (higher CE/RMSE). Moreover, the sustained group’s capacity to minimize SD/RMSE/CE corresponded to a more complex structure in their force fluctuations. These findings reveal that the time component of MVC estimation has a direct influence on the corrective strategies supporting near-maximal manual force control. While discrete MVC protocols predominate in the study of manual strength/endurance/precision, a 1:1 MVC-task mapping appears more to be ecologically valid if visuo-motor precision outcomes are of central importance.

Fatigue following mild traumatic brain injury relates to visual processing and effort perception in the context of motor performance

IntroductionFollowing mild traumatic brain injury (mTBI), a substantial number of patients experience disabling fatigue for months after the initial injury. To date, the underlying mechanisms of fatigue remain unclear. Recently, it was shown that mTBI patients with persistent fatigue do not demonstrate increased performance fatigability (i.e., objective performance decline) during a sustained motor task. However, it is not known whether the neural activation required to sustain this performance is altered after mTBI. MethodsBlood oxygen level-dependent (BOLD) fMRI data were acquired from 19 mTBI patients (>3 months post-injury) and 19 control participants during two motor tasks. Force was recorded from the index finger abductors of both hands during submaximal contractions and a 2-minute maximal voluntary contraction (MVC) with the right hand. Voluntary muscle activation (i.e., CNS drive) was indexed during the sustained MVC using peripheral nerve stimulation. Fatigue was quantified using the Fatigue Severity Scale (FSS) and Modified Fatigue Impact Scale (MFIS). Questionnaire, task, and BOLD data were compared across groups, and linear regression was used to evaluate the relationship between BOLD-activity and fatigue in the mTBI group. ResultsThe mTBI patients reported significantly higher levels of fatigue (FSS: 5.3 vs. 2.6, p < 0.001). Both mTBI- and control groups demonstrated significant performance fatigability during the sustained MVC, but no significant differences in task performance or BOLD-activity were observed between groups. However, mTBI patients reporting higher FSS scores showed increased BOLD-activity in the bilateral visual cortices (mainly extrastriate) and the left midcingulate gyrus. Furthermore, across all participants mean voluntary muscle activation during the sustained MVC correlated with long lasting post-contraction BOLD-activation in the right insula and midcingulate cortex. ConclusionThe fMRI findings suggest that self-reported fatigue in mTBI may relate to visual processing and effort perception. Long lasting activation associated with high levels of CNS drive might be related to changes in cortical homeostasis in the context of high effort.

Oxygen availability affects exercise capacity, but not neuromuscular fatigue characteristics of knee extensors, during exhaustive intermittent cycling.

To compare the effects of different hypoxia severities on exercise capacity, cardio-respiratory, tissue oxygenation and neuromuscular fatigue characteristics in response to exhaustive intermittent cycling. Eleven well-trained cyclists, repeated supra-maximal cycling efforts of 15s (30% of anaerobic power reserve, 609 ± 23W), interspersed with 45s of passive rest until task failure. The exercise was performed on separate days in normoxia (SL; simulated altitude/end-exercise arterial oxygen saturation = 0m/~ 96%), moderate (MH; 2200m/~ 90%) and severe (SH; 4200m/~ 79%) hypoxia in a cross-over design. Neuromuscular tests, including brief (5s) and sustained (30s) maximal isometric voluntary contractions of the knee extensors, were performed at baseline and exhaustion. Exercise capacity decreased with hypoxia severity (23 ± 9, 16 ± 6 and 9 ± 3 cycle efforts in SL, MH and SH, respectively; P < 0.001; η2 = 0.72). Both cerebral (P < 0.001; η2 = 0.86) and muscle (P < 0.01; η2 = 0.54) oxygenation decreased throughout the exercise, independent of condition (P ≥ 0.45; η2 ≥ 0.14). Compared to SL, muscle oxygenation was globally lower in MH and SH (P = 0.011; η2 = 0.36). Cardiovascular solicitation neared maximal values at exhaustion in all conditions. Peak twitch amplitude with single and paired electrical stimuli (P < 0.001; η2 ≥ 0.87), maximal torque (P < 0.001; η2 ≥ 0.48) and voluntary activation measured using transcranial magnetic stimulation (P ≤ 0.034; η2 ≥ 0.31) during brief and sustained MVCs were all reduced at exhaustion, independent of condition (P ≥ 0.196; η2 ≥ 0.15). Despite reduced exercise capacity with increasing severity of hypoxia during exhaustive intermittent cycling, neuromuscular fatigue characteristics were not different at task failure and cardiovascular solicitation neared maximum values.

Time course of neuromuscular responses to acute hypoxia during voluntary contractions.

What is the central question of this study? How does acute hypoxia alter central and peripheral fatigue during brief and sustained maximal voluntary muscle contractions? What is the main finding and its importance? Perception of fatigue during muscle contractions was increased progressively for 2 h after hypoxic exposure. However, an increase in motor cortex excitability and a decrease in voluntary activation of skeletal muscle were observed across the entire protocol when performing brief (3 s) maximal contractions. These adaptations were abolished if the brief contraction was held for a duration of 20 s, which was presumably attributable to a successful redistribution of blood to overcome the reduced oxygen content. Few studies have examined the time course of changes in the motor system after acute exposure to hypoxia. Thus, the purpose of this study was to examine how acute hypoxia affects corticospinal excitability, voluntary activation (VA) and the perception of fatigue during brief (3s) and sustained (20s) maximal voluntary contractions (MVCs). Fourteen healthy individuals (23±2.2years of age; four female) were exposed to hypoxia and sham conditions. During hypoxia, peripheral blood oxygen saturation was titrated over a 15min period and remained at 80% during testing. Corticospinal excitability and VA were assessed before titration (Pre), 0, 1 and 2 h after. At each time point, the brief and sustained elbow flexion MVCs were performed. Motor evoked potentials (MEPs) were obtained using transcranial magnetic stimulation. Superimposed and resting twitches were obtained from motor point stimulation of biceps brachii to calculate the level of VA, and ratings of perceived fatigue were obtained with a modified CR-10 Borg scale. A condition-by-time interaction was detected for the CR-10 Borg scale, whereby perception of fatigue increased progressively throughout the hypoxia protocol. However, main effects of MEP area and VA indicated that corticospinal excitability increased, and VA of the biceps brachii decreased, throughout the hypoxia protocol. Given that these changes in MEP area and VA were seen only when performing the brief MVCs (and not during the sustained MVCs), performing longer contractions might overcome reduced oxygen content by redirecting blood flow to active areas of the motor system.

The effect of head and neck per-cooling on neuromuscular fatigue following exercise in the heat.

The effect of localised head and neck per-cooling on central and peripheral fatigue during high thermal strain was investigated. Fourteen participants cycled for 60 min at 50% peak oxygen uptake on 3 occasions: thermoneutral control (CON; 18 °C), hot (HOT; 35 °C), and HOT with head and neck cooling (HOTcooling). Maximal voluntary force (MVF) and central activation ratio (CAR) of the knee extensors were measured every 30 s during a sustained maximal voluntary contraction (MVC). Triplet peak force was measured following cycling, before and after the MVC. Rectal temperatures were higher in HOTcooling (39.2 ± 0.6 °C) and HOT (39.3 ± 0.5 °C) than CON (38.1 ± 0.3 °C; P < 0.05). Head and neck thermal sensation was similar in HOTcooling (4.2 ± 1.4) and CON (4.4 ± 0.9; P > 0.05) but lower than HOT (5.9 ± 1.5; P < 0.05). MVF and CAR were lower in HOT than CON throughout the MVC (P < 0.05). MVF and CAR were also lower in HOTcooling than CON at 5, 60, and 120 s, but similar at 30 and 90 s into the MVC (P > 0.05). Furthermore, they were greater in HOTcooling than HOT at 30 s, whilst triplet peak force was preserved in HOT after MVC. These results provide evidence that central fatigue following exercise in the heat is partially attenuated with head and neck cooling, which may be at the expense of greater peripheral fatigue. Novelty Central fatigue was greatest during hyperthermia. Head and neck cooling partially attenuated the greater central fatigue in the heat. Per-cooling led to more voluntary force production and more peripheral fatigue.