ORCID Profile
0000-0002-5790-7514
Current Organisation
University of Birmingham
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: Society for Neuroscience
Date: 02-09-2015
DOI: 10.1523/JNEUROSCI.0240-15.2015
Abstract: Neural control of synergist muscles is not well understood. Presumably, each muscle in a synergistic group receives some unique neural drive and some drive that is also shared in common with other muscles in the group. In this investigation, we sought to characterize the strength, frequency spectrum, and force dependence of the neural drive to the human vastus lateralis and vastus medialis muscles during the production of isometric knee extension forces at 10 and 30% of maximum voluntary effort. High-density surface electromyography recordings were decomposed into motor unit action potentials to examine the neural drive to each muscle. Motor unit coherence analysis was used to characterize the total neural drive to each muscle and the drive shared between muscles. Using a novel approach based on partial coherence analysis, we were also able to study specifically the neural drive unique to each muscle (not shared). The results showed that the majority of neural drive to the vasti muscles was a cross-muscle drive characterized by a force-dependent strength and bandwidth. Muscle-specific neural drive was at low frequencies ( Hz) and relatively weak. Frequencies of neural drive associated with afferent feedback (6–12 Hz) and with descending cortical input (∼20 Hz) were almost entirely shared by the two muscles, whereas low-frequency ( Hz) drive comprised shared (primary) and muscle-specific (secondary) components. This study is the first to directly investigate the extent of shared versus independent control of synergist muscles at the motor neuron level. SIGNIFICANCE STATEMENT Precisely how the nervous system coordinates the activity of synergist muscles is not well understood. One possibility is that muscles of a synergy share a common neural drive. In this study, we directly compared the relative strength of shared versus independent neural drive to synergistically activated thigh muscles in humans. The results of this analysis support the notion that synergistically activated muscles share most of their neural drive. Scientifically, this study addressed an important gap in our current understanding of how neural drive is delivered to synergist muscles. We have also demonstrated the feasibility of a novel approach to the study of muscle synergies based on partial coherence analysis of motor unit activity.
Publisher: American Physiological Society
Date: 10-2019
DOI: 10.1152/JAPPLPHYSIOL.00310.2019
Abstract: Conflicting results have been reported on whether closed kinetic chain exercises (such as a leg press) may induce more balanced activation of vastus medialis (VM) and lateralis (VL) muscles compared with open kinetic chain exercise (such as pure knee extension). This study aimed to 1) compare between-vasti motor unit activity and 2) analyze the combined motor unit behavior from both muscles between open and closed kinetic chain exercises. Thirteen participants (four women, mean ± SD age: 27 ± 5 yr) performed isometric knee extension and leg press at 10, 30, 50, 70% of the maximum voluntary torque. High density surface EMG signals were recorded from the VM and VL and motor unit firings were automatically identified by convolutive blind source separation. We estimated the total synaptic input received by the two muscles by analyzing the difference in discharge rate from recruitment to target torque for motor units matched by recruitment threshold. When controlling for recruitment threshold and discharge rate at recruitment, the motor unit discharge rates were higher for knee extension compared with the leg press exercise at 50% [estimate = 1.2 pulses per second (pps), standard error (SE) = 0.3 pps,
Publisher: American Physiological Society
Date: 10-2021
DOI: 10.1152/JAPPLPHYSIOL.01011.2020
Abstract: Pain induces changes in motor performance, motor unit recruitment, and rate coding behavior that varies across different contraction speeds. Here we show that that pain reduces motor unit discharge rate and prolongs the neuromechanical delay at slow contraction speeds only. This new evidence suggests that there are differential nociceptive inhibitory effects across the motor unit pool, which allows fast submaximal contractions to be exerted despite the presence of pain.
Publisher: Public Library of Science (PLoS)
Date: 14-06-2023
DOI: 10.1371/JOURNAL.PONE.0287029
Abstract: Variability in spine kinematics is a common motor adaptation to pain, which has been measured in various ways. However, it remains unclear whether low back pain (LBP) is typically characterised by increased, decreased or unchanged kinematic variability. Therefore, the aim of this review was to synthesise the evidence on whether the amount and structure of spine kinematic variability is altered in people with chronic non-specific LBP (CNSLBP). Electronic databases, grey literature, and key journals were searched from inception up to August 2022, following a published and registered protocol. Eligible studies must investigated kinematic variability in CNSLBP people (adults ≥18 years) while preforming repetitive functional tasks. Two reviewers conducted screening, data extraction, and quality assessment independently. Data synthesis was conducted per task type and in idual results were presented quantitatively to provide a narrative synthesis. The overall strength of evidence was rated using the Grading of Recommendations, Assessment, Development and Evaluation guidelines. Fourteen observational studies were included in this review. To facilitate the interpretation of the results, the included studies were grouped into four categories according to the task preformed (i.e., repeated flexion and extension, lifting, gait, and sit to stand to sit task). The overall quality of evidence was rated as a very low, primarily due to the inclusion criteria that limited the review to observational studies. In addition, the use of heterogeneous metrics for analysis and varying effect sizes contributed to the downgrade of evidence to a very low level. In iduals with chronic non-specific LBP exhibited altered motor adaptability, as evidenced by differences in kinematic movement variability during the performance of various repetitive functional tasks. However, the direction of the changes in movement variability was not consistent across studies.
Publisher: Wiley
Date: 23-10-2015
DOI: 10.1111/SMS.12578
Abstract: We studied the sensitivity of electromyographic (EMG) variables to load and muscle fatigue during continuous and intermittent incremental cycling. Fifteen men attended three laboratory sessions. Visit 1: lactate threshold, peak power output, and VO
Publisher: Cold Spring Harbor Laboratory
Date: 28-04-2021
DOI: 10.1101/2021.04.27.441619
Abstract: The integration of electromyography (EMG) and ultrasound imaging has provided important information about the mechanisms of muscle activation and contraction. Unfortunately, EMG does not allow an accurate assessment of the interplay between the neural drive received by muscles, changes in fascicle length (FL) and the force/torque produced. We aimed to assess the relationship between modulations in tibialis anterior (TA) motor unit (MU) firing rate, FL and dorsiflexion torque (DT) using ultrasound-transparent high-density EMG electrodes. EMG and ultrasound images were recorded simultaneously from TA, using a 32-electrode silicon matrix, while performing isometric dorsiflexion, at erse ankle joint positions (0° and 30° plantar flexion) and torques (20% and 40% of maximum). EMG signals were decomposed into in idual MUs and changes in FL were assessed with a fascicle-tracking algorithm. MU firings were converted into a cumulative spike train (CST) that was cross-correlated with DT (CST-DT) and FL (CST-FL). High cross-correlations were found for CST-FL, 0.60 (range: 0.31-0.85) and CST-DT 0.71 (range: 0.31-0.88). Cross-correlation lags revealed that the delay between CST-FL (~75ms) was significantly smaller than CST-DT (~150ms, p .001). These delays affected the interpretation of MU recruitment/de-recruitment thresholds, with FL showing similar lengths for both recruitment and de-recruitment. This study is the first to demonstrate that changes in TA FL are closely related to both modulations in MU firing frequency and DT. These relationships allow assessment of the interplay between neural drive, muscle contraction and resultant torque, thereby providing a better understanding of the mechanisms responsible for the generation of muscle force. By employing ultrasound-transparent high-density surface EMG electrodes, we show that modulations in tibialis anterior motor unit discharge rate were closely related to both changes in its fascicle length and resultant torque. These relationships allowed quantifying delays between neural drive and muscle shortening as well as muscle shortening and torque during submaximal isometric contractions, providing an accurate estimation of the time required to generate muscle force and subsequent production of torque via the tendon.
Publisher: BMJ
Date: 05-2021
DOI: 10.1136/BMJOPEN-2020-046064
Abstract: Motor variability is an important feature when performing repetitive movement, and in asymptomatic people functional tasks are typically performed with variable motor patterns. However, in the presence of chronic non-specific low back pain (LBP), people often present with different motor control strategies than those without pain. Movement variability has been assessed using a wide range of variables, including kinetic and kinematic components of motion. This has resulted in a wide range of findings reported in the literature and some contradicting results. Therefore, the aim of this systematic review is to investigate whether the amount and structure of motor variability are altered in people with chronic non-specific LBP, during both repetitive non-functional and functional tasks. This protocol for a systematic review is informed by Cochrane guidelines and reported in line with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis Protocols. MEDLINE, EMBASE, CINAHL, ZETOC, Web of Science, PubMed and Scopus will be searched from their inception to December 2020 along with a comprehensive search of grey literature and key journals. Two independent reviewers will conduct the search, extract the data, assess risk of bias (using the Downs and Black Scale) for the included studies and assess overall quality of evidence based on Grading of Recommendations, Assessment, Development and Evaluation guidelines. Meta-analysis will be conducted if deemed appropriate. Alternatively, a narrative synthesis will be conducted and evidence summarised as an increase, decrease or no change in the motor variability of people with LBP compared with healthy controls. This study raises no ethical issues. Results will be submitted for publication in a peer review journal and presented at conferences. CRD42020211580.
Publisher: American Physiological Society
Date: 11-2022
DOI: 10.1152/JAPPLPHYSIOL.00758.2021
Abstract: By employing ultrasound-transparent high-density EMG electrodes, we show that modulations in tibialis anterior muscle motor unit discharge rate were related to both changes in fascicle length and resultant torque. These relationships permitted the quantification of the relative delays between fluctuations in neural drive, muscle contraction, and transfer of torque via the tendon during sustained isometric dorsiflexion contractions, providing information on the conversion of neural activity into muscle force during a contraction.
Publisher: Wiley
Date: 29-04-2020
DOI: 10.1113/JP279225
Publisher: Wiley
Date: 25-06-2021
DOI: 10.1002/EJP.1789
Abstract: Numerous studies have examined the influence of pain on spinal reflex excitability, motor unit behaviour and corticospinal excitability. Nevertheless, there are inconsistencies in the conclusions made. This systematic review sought to understand the effect of pain on spinal and supraspinal projections to motoneurons and motor unit properties by examining the influence of clinical or experimental pain on the following three domains: H‐reflex, corticospinal excitability and motor unit properties. MeSH terms and preselected keywords relating to the H‐reflex, motor evoked potentials and motor unit decomposition in chronic and experimental pain were used to perform a systematic literature search using Cumulative Index of Nursing and Allied Health Literature (CINAHL), Excerpta Medica dataBASE (EMBASE), Web of Science, Medline, Google Scholar and Scopus databases. Two independent reviewers screened papers for inclusion and assessed the methodological quality using a modified Downs and Black risk of bias tool a narrative synthesis and three meta‐analyses were performed. Sixty‐one studies were included, and 17 different outcome variables were assessed across the three domains. Both experimental and clinical pain have no major influence on measures of the H‐reflex, whereas experimental and clinical pain appeared to have differing effects on corticospinal excitability. Experimental pain consistently reduced motor unit discharge rate, a finding which was not consistent with data obtained from patients. The results indicate that when in tonic pain, induced via experimental pain models, inhibitory effects on motoneuron behaviour were evident. However, in chronic clinical pain populations, more varied responses were evident likely reflecting in idual adaptations to chronic symptoms. This is a comprehensive systematic review and meta‐analysis which synthesizes evidence on the influence of pain on spinal and supraspinal projections to motoneurons and motor unit properties considering measures of the H‐reflex, corticospinal excitability and motor unit behaviour. The H‐reflex is largely not influenced by the presence of either clinical or experimental pain. Whilst inhibitory effects on corticospinal excitability and motor unit behaviour were evident under experimental pain conditions, more variable responses were observed for people with painful musculoskeletal disorders.
Publisher: American Physiological Society
Date: 04-2018
DOI: 10.1152/JAPPLPHYSIOL.01115.2017
Abstract: Surface electromyographic (EMG) signal litude is typically used to compare the neural drive to muscles. We experimentally investigated this association by studying the motor unit (MU) behavior and action potentials in the vastus medialis (VM) and vastus lateralis (VL) muscles. Eighteen participants performed isometric knee extensions at four target torques [10, 30, 50, and 70% of the maximum torque (MVC)] while high-density EMG signals were recorded from the VM and VL. The absolute EMG litude was greater for VM than VL ( P 0.001), whereas the EMG litude normalized with respect to MVC was greater for VL than VM ( P 0.04). Because differences in EMG litude can be due to both differences in the neural drive and in the size of the MU action potentials, we indirectly inferred the neural drives received by the two muscles by estimating the synaptic inputs received by the corresponding motor neuron pools. For this purpose, we analyzed the increase in discharge rate from recruitment to target torque for motor units matched by recruitment threshold in the two muscles. This analysis indicated that the two muscles received similar levels of neural drive. Nonetheless, the size of the MU action potentials was greater for VM than VL ( P 0.001), and this difference explained most of the differences in EMG litude between the two muscles (~63% of explained variance). These results indicate that EMG litude, even following normalization, does not reflect the neural drive to synergistic muscles. Moreover, absolute EMG litude is mainly explained by the size of MU action potentials. NEW & NOTEWORTHY Electromyographic (EMG) litude is widely used to compare indirectly the strength of neural drive received by synergistic muscles. However, there are no studies validating this approach with motor unit data. Here, we compared between-muscles differences in surface EMG litude and motor unit behavior. The results clarify the limitations of surface EMG to interpret differences in neural drive between muscles.
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 06-2017
Publisher: Ovid Technologies (Wolters Kluwer Health)
Date: 11-2018
DOI: 10.1249/MSS.0000000000001705
Abstract: Moderate-intensity continuous training (MICT) and high-intensity interval training (HIIT) are associated with different adjustments in motor output. Changes in motor unit (MU) peripheral properties may contribute to these adjustments, but this is yet to be elucidated. This study evaluated early changes in MU conduction velocity (MUCV) and MU action potential litude after 2 wk of either HIIT or MICT. Sixteen men were assigned to either an MICT group or HIIT group ( n = 8 each), and participated in six training sessions over 14 d. HIIT: 8 to 12 × 60-s intervals at 100% peak power output. Moderate-intensity continuous training: 90 to 120 min continuous cycling at ~65% V˙O 2peak . Preintervention and postintervention, participants performed maximal voluntary contractions (MVC) and submaximal (10%, 30%, 50%, and 70% of MVC) isometric knee extensions while high-density EMG was recorded from the vastus medialis (VM) and vastus lateralis (VL) muscles. The high-density EMG was decomposed into in idual MU by convolutive blind-source separation and tracked preintervention and postintervention. Both training interventions induced changes in MUCV, but these changes depended on the type of training ( P 0.001). The HIIT group showed higher values of MUCV after training at all torque levels ( P 0.05), MICT only displayed changes in MUCV at low torque levels (10%–30% MVC, P 0.002). There were no changes in MU action potential litude for either group ( P = 0.2). Two weeks of HIIT or MICT elicit differential changes in MUCV, likely due to the contrasting load and volume used in such training regimes. This new knowledge on the neuromuscular adaptations to training has implications for exercise prescription.
Publisher: Elsevier BV
Date: 11-2019
DOI: 10.1016/J.JSAMS.2019.07.007
Abstract: Despite the high prevalence of low back pain (LBP) in rowers, there are few studies investigating changes in lumbar muscle activation in rowers with a recent history of LBP. Such knowledge is relevant to understand potential mechanisms contributing to the maintenance and recurrence of LBP in rowers. For the first time, we evaluate the spatial distribution of erector spinae (ES) activity in rowers with and without a recent history of LBP, using a novel application of high-density surface electromyography (HDEMG). Cross-sectional study. Asymptomatic rowers (N=10) and rowers with a recent history of LBP (N=8) performed 7×4-min exercise bouts (rowing ergometer) until volitional exhaustion. HDEMG signals were acquired bilaterally over the lumbar ES and the root mean square (RMS) litude and entropy were analyzed. In addition, the y-axis coordinate of the barycentre (RMS-map) was used to assess changes in ES spatial activation. As the load increased, rowers with LBP showed higher litude (p<0.01) and less complexity (entropy) of the HDEMG signals (p<0.001). In addition, rowers with LBP showed opposite displacements of the barycentre, specifically showing a caudal shift of muscle activity at high intensities (p<0.001). Both the magnitude of activation and distribution of ES activity were altered in rowers with a recent history of LBP. The lower complexity of signals together with the caudal displacements of the barycentre suggest an inefficient recruitment of the ES as the load progressed. Modification of the rowing technique in conjunction with feedback from HDEMG might prove useful in future studies.
Publisher: Springer Science and Business Media LLC
Date: 16-03-2018
Publisher: Wiley
Date: 28-02-2017
DOI: 10.1113/JP273662
Publisher: American Physiological Society
Date: 10-2020
Abstract: Motor unit firing and contractile properties during a submaximal contraction until failure were assessed with a new tracking technique. Two distinct phases in firing behavior were observed, which compensated for changes in twitch area and predicted time to failure. However, the late increase in firing rate was below the rates attained in the absence of fatigue, which points to an inability of the central nervous system to sufficiently increase the neural drive to muscle with fatigue.
Publisher: BMJ
Date: 2021
DOI: 10.1136/BMJOPEN-2020-042525
Abstract: Performing contractions with minimum force fluctuations is essential for everyday life as reduced force steadiness impacts on the precision of voluntary movements and functional ability. Several studies have investigated the effect of experimental or clinical musculoskeletal pain on force steadiness but with conflicting findings. The aim of this systematic review is to summarise the current literature to determine whether pain, whether it be clinical or experimental, influences force steadiness. This protocol for a systematic review was informed and reported in line with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols and the Cochrane Handbook for Systematic Reviews of Interventions. Key databases will be searched from inception to 31 August 2020, including MEDLINE, EMBASE, PubMed, CINAHL Plus, ZETOC and Web of Science. Grey literature and key journals will be also reviewed. Risk of bias will be assessed with the Newcastle-Ottawa tool, and the quality of the cumulative evidence assessed with the Grading of Recommendations, Assessment, Development and Evaluation guidelines. If homogeneity exists between groups of studies, meta-analysis will be conducted. Otherwise, a narrative synthesis approach and a vote-counting method will be used, while the results will be presented as net increases or decreases of force steadiness. The findings will be presented at conferences and the review will be also submitted for publication in a refereed journal. No ethical approval was required. CRD42020196479
Publisher: BMJ
Date: 02-2022
DOI: 10.1136/BMJOPEN-2021-050186
Abstract: Achilles tendinopathy (AT) is a debilitating overuse injury characterised by pain, impaired functional performance, morpho-mechanical changes to the Achilles tendon and triceps surae neuromuscular alterations. Loading-based exercise has become the principal non-surgical choice for the treatment of AT however, mechanistic evidence by which loading-based treatment may help to resolve tendon pain remains unclear. This systematic review aims to summarise the evidence of the neuromechanical changes produced by AT and by exercise-induced mechanical loading. This systematic review protocol was informed and reported in accordance with the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA-P) and the Cochrane Handbook for Systematic Reviews of Interventions. Pubmed, MEDLINE, EMBASE, CINAHL Plus, Web of Science and SPORTDiscus electronic databases will be searched from inception to February 2021. Additionally, grey literature and key journals will be reviewed. Risk of bias will be determined independently by two reviewers using the version 2 of the Cochrane risk-of-bias tool for randomised trials (RoB 2) and the risk of bias in non-randomised studies - of interventions (ROBINS-I) tool according to Cochrane recommendations. Quality of the cumulative evidence will be assessed with the Grading of Recommendations, Assessment, Development, and Evaluation (GRADE) guidelines. If homogeneity exists between groups of studies, a random-effects meta-analysis will be conducted. If not, results will be synthesised narratively. Our findings will be disseminated through publication in a peer-reviewed journal and presented at conferences. No ethical approval was required. CRD42021231933.
Publisher: BMJ
Date: 07-2022
DOI: 10.1136/BMJOPEN-2021-058683
Abstract: There is limited evidence on the neural strategies employed by the central nervous system to control muscle force in the presence of non-insertional Achilles tendinopathy (NIAT). Additionally, the neuromuscular mechanisms by which exercise may help to resolve tendon pain remain unclear. This study aims to first establish changes in the gastrocnemius-soleus motor unit firing properties after applying a training protocol of 6 weeks based on either controlled eccentric or concentric contractions in in iduals with NIAT. Second, we want to determine changes in the level of pain and function and mechanical and structural properties of the Achilles tendon after applying the same training protocol. Additionally, we want to compare these variables at baseline between in iduals with NIAT and asymptomatic controls. A total of 26 in iduals with chronic ( months) NIAT and 13 healthy controls will participate in the study. In iduals with NIAT will be randomised to perform eccentric or concentric training for 6 weeks. Motor unit firing properties of the medial gastrocnemius, lateral gastrocnemius and soleus muscles will be assessed using high-density surface electromyography, as well as Achilles tendon length, cross-sectional area, thickness and stiffness using B-mode ultrasonography and shear wave elastography. Moreover, participants will complete a battery of questionnaires to document their level of pain and function. Ethical approval (ERN-20-0604A) for the study was obtained from the Science, Technology, Engineering and Mathematics Ethical Review Committee of the University of Birmingham. The results of the study will be published in peer-review journals. ISRCTN46462385 .
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Eduardo Martinez-Valdes.