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Is the 'reverse onion skin' phenomenon more prevalent than we thought during intramuscular myoelectric recordings from low to maximal force outputs? Neurosci Lett 2020; 743:135583. [PMID: 33352279 DOI: 10.1016/j.neulet.2020.135583] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2020] [Revised: 12/10/2020] [Accepted: 12/14/2020] [Indexed: 11/21/2022]
Abstract
There are isolated instances in the literature that suggest the 'onion skin' phenomenon is not always present. That is, newly recruited high threshold motor units (MU) have higher discharge rates than previously recruited low threshold MUs. Therefore, the purpose of this paper was to investigate the presence of the 'onion skin' phenomenon in a large sample of intramuscular myoelectric recordings from low to maximal force outputs. Forty-eight participants performed rapid isometric dorsiflexion contractions at 20, 40, 60, 80 and 100 % MVC while intramuscular electrical activity was recorded. A bivariate frequency-distribution of the motor unit discharge rate and motor unit action potential peak-to-peak (P-P) amplitude was assessed. There was a significant difference in bivariate frequency-distribution across force levels (D's = 0.1083-0.3094, p's < 0.001). Newly recruited high threshold MUs did have lower discharge rates, but there was an increase in the presence of high threshold, large P-P amplitude MUs with higher discharge rates than lower threshold MUs (reverse onion skin) during the stable portion of the force output. The recruitment of high threshold MUs with higher discharge rates decreased the level of common drive from the cross-correlation (Rxy) = 0.79 at 20 % MVC to Rxy = 0.68 at 100 % MVC (p < 0.01), but it remained high. As the interference pattern becomes more complex with the recruitment of more motor units at higher force outputs, intramuscular electrodes may be more discriminating while recording motor unit activity leading to the identification of both the 'reverse onion skin' and 'onion skin' phenomenon being present.
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Zhou Y, Bi Z, Ji M, Chen S, Wang W, Wang K, Hu B, Lu X, Wang Z. A Data-Driven Volitional EMG Extraction Algorithm During Functional Electrical Stimulation With Time Variant Parameters. IEEE Trans Neural Syst Rehabil Eng 2020; 28:1069-1080. [DOI: 10.1109/tnsre.2020.2980294] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Chen YC, Lin YT, Chang GC, Hwang IS. Paradigm Shifts in Voluntary Force Control and Motor Unit Behaviors with the Manipulated Size of Visual Error Perception. Front Physiol 2017; 8:140. [PMID: 28348530 PMCID: PMC5346555 DOI: 10.3389/fphys.2017.00140] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2016] [Accepted: 02/23/2017] [Indexed: 12/13/2022] Open
Abstract
The detection of error information is an essential prerequisite of a feedback-based movement. This study investigated the differential behavior and neurophysiological mechanisms of a cyclic force-tracking task using error-reducing and error-enhancing feedback. The discharge patterns of a relatively large number of motor units (MUs) were assessed with custom-designed multi-channel surface electromyography following mathematical decomposition of the experimentally-measured signals. Force characteristics, force-discharge relation, and phase-locking cortical activities in the contralateral motor cortex to individual MUs were contrasted among the low (LSF), normal (NSF), and high scaling factor (HSF) conditions, in which the sizes of online execution errors were displayed with various amplification ratios. Along with a spectral shift of the force output toward a lower band, force output with a more phase-lead became less irregular, and tracking accuracy was worse in the LSF condition than in the HSF condition. The coherent discharge of high phasic (HP) MUs with the target signal was greater, and inter-spike intervals were larger, in the LSF condition than in the HSF condition. Force-tracking in the LSF condition manifested with stronger phase-locked EEG activity in the contralateral motor cortex to discharge of the (HP) MUs (LSF > NSF, HSF). The coherent discharge of the (HP) MUs during the cyclic force-tracking predominated the force-discharge relation, which increased inversely to the error scaling factor. In conclusion, the size of visualized error gates motor unit discharge, force-discharge relation, and the relative influences of the feedback and feedforward processes on force control. A smaller visualized error size favors voluntary force control using a feedforward process, in relation to a selective central modulation that enhance the coherent discharge of (HP) MUs.
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Affiliation(s)
- Yi-Ching Chen
- School of Physical Therapy, Chung Shan Medical UniversityTaichung, Taiwan; Physical Therapy Room, Chung Shan Medical University HospitalTaichung, Taiwan
| | - Yen-Ting Lin
- Physical Education Room, Asian University Taichung, Taiwan
| | - Gwo-Ching Chang
- Department of Information Engineering, I-Shou University Kaohsiung, Taiwan
| | - Ing-Shiou Hwang
- Institute of Allied Health Sciences, College of Medicine, National Cheng Kung UniversityTainan, Taiwan; Department of Physical Therapy, College of Medicine, National Cheng Kung UniversityTainan, Taiwan
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Wang ZG, Wang HP, Bi ZY, Zhou Y, Zhou YX, Lv XY. Real-time and wearable functional electrical stimulation system for volitional hand motor function control using the electromyography bridge method. Neural Regen Res 2017. [DOI: 10.4103/1673-5374.199216] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022] Open
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Wang HP, Bi ZY, Zhou Y, Zhou YX, Wang ZG, Lv XY. Real-time and wearable functional electrical stimulation system for volitional hand motor function control using the electromyography bridge method. Neural Regen Res 2017; 12:133-142. [PMID: 28250759 PMCID: PMC5319219 DOI: 10.4103/1673-5374.197139] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022] Open
Abstract
Voluntary participation of hemiplegic patients is crucial for functional electrical stimulation therapy. A wearable functional electrical stimulation system has been proposed for real-time volitional hand motor function control using the electromyography bridge method. Through a series of novel design concepts, including the integration of a detecting circuit and an analog-to-digital converter, a miniaturized functional electrical stimulation circuit technique, a low-power super-regeneration chip for wireless receiving, and two wearable armbands, a prototype system has been established with reduced size, power, and overall cost. Based on wrist joint torque reproduction and classification experiments performed on six healthy subjects, the optimized surface electromyography thresholds and trained logistic regression classifier parameters were statistically chosen to establish wrist and hand motion control with high accuracy. Test results showed that wrist flexion/extension, hand grasp, and finger extension could be reproduced with high accuracy and low latency. This system can build a bridge of information transmission between healthy limbs and paralyzed limbs, effectively improve voluntary participation of hemiplegic patients, and elevate efficiency of rehabilitation training.
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Affiliation(s)
- Hai-Peng Wang
- Institute of RF- & OE-ICs, Southeast University, Nanjing, Jiangsu Province, China
| | - Zheng-Yang Bi
- State Key Lab of Bioelectronics, Southeast University, Nanjing, Jiangsu Province, China
| | - Yang Zhou
- Institute of RF- & OE-ICs, Southeast University, Nanjing, Jiangsu Province, China
| | - Yu-Xuan Zhou
- State Key Lab of Bioelectronics, Southeast University, Nanjing, Jiangsu Province, China
| | - Zhi-Gong Wang
- Institute of RF- & OE-ICs, Southeast University, Nanjing, Jiangsu Province, China; Co-innovation Center of Neuroregeneration, Nantong University, Nantong, Jiangsu Province, China
| | - Xiao-Ying Lv
- State Key Lab of Bioelectronics, Southeast University, Nanjing, Jiangsu Province, China; Co-innovation Center of Neuroregeneration, Nantong University, Nantong, Jiangsu Province, China
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6
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Zhou YX, Wang HP, Bao XL, Lü XY, Wang ZG. A frequency and pulse-width co-modulation strategy for transcutaneous neuromuscular electrical stimulation based on sEMG time-domain features. J Neural Eng 2015; 13:016004. [DOI: 10.1088/1741-2560/13/1/016004] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Röhrle O, Davidson JB, Pullan AJ. A physiologically based, multi-scale model of skeletal muscle structure and function. Front Physiol 2012; 3:358. [PMID: 22993509 PMCID: PMC3440711 DOI: 10.3389/fphys.2012.00358] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2012] [Accepted: 08/20/2012] [Indexed: 11/28/2022] Open
Abstract
Models of skeletal muscle can be classified as phenomenological or biophysical. Phenomenological models predict the muscle's response to a specified input based on experimental measurements. Prominent phenomenological models are the Hill-type muscle models, which have been incorporated into rigid-body modeling frameworks, and three-dimensional continuum-mechanical models. Biophysically based models attempt to predict the muscle's response as emerging from the underlying physiology of the system. In this contribution, the conventional biophysically based modeling methodology is extended to include several structural and functional characteristics of skeletal muscle. The result is a physiologically based, multi-scale skeletal muscle finite element model that is capable of representing detailed, geometrical descriptions of skeletal muscle fibers and their grouping. Together with a well-established model of motor-unit recruitment, the electro-physiological behavior of single muscle fibers within motor units is computed and linked to a continuum-mechanical constitutive law. The bridging between the cellular level and the organ level has been achieved via a multi-scale constitutive law and homogenization. The effect of homogenization has been investigated by varying the number of embedded skeletal muscle fibers and/or motor units and computing the resulting exerted muscle forces while applying the same excitatory input. All simulations were conducted using an anatomically realistic finite element model of the tibialis anterior muscle. Given the fact that the underlying electro-physiological cellular muscle model is capable of modeling metabolic fatigue effects such as potassium accumulation in the T-tubular space and inorganic phosphate build-up, the proposed framework provides a novel simulation-based way to investigate muscle behavior ranging from motor-unit recruitment to force generation and fatigue.
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Affiliation(s)
- O Röhrle
- Institute of Applied Mechanics (Civil Engineering), University of Stuttgart Stuttgart, Germany ; Cluster of Excellence for Simulation Technology, University of Stuttgart Stuttgart, Germany
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Mrówczyński W, Celichowski J, Krutki P, Cabaj A, Sławińska U, Majczyński H. Changes of the force-frequency relationship in the rat medial gastrocnemius muscle after total transection and hemisection of the spinal cord. J Neurophysiol 2011; 105:2943-50. [DOI: 10.1152/jn.00687.2010] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The relationships between the stimulation frequency and the force developed by motor units (MUs) of the medial gastrocnemius muscle were compared between intact rats and animals after total transection or hemisection of the spinal cord at the low thoracic level. The experiments on functionally isolated MUs were carried out 14, 30, 90, and 180 days after the spinal cord injury. Axons of investigated MUs were stimulated with trains of pulses at 10 progressively increased frequencies (from 1 to 150 Hz), and the force-frequency curves were plotted. Spinal cord hemisection resulted in a considerable leftward shift of force-frequency curves in all types of MUs. After the total transection, a leftward shift of the curve was observed in fast MUs, whereas there was a rightward shift in slow MUs. These changes coincided with a decrease of stimulation frequencies necessary to evoke 60% of maximal force. Moreover, the linear correlation between these stimulation frequencies and the twitch contraction time observed in intact rats was disrupted in all groups of animals with spinal cord injury. The majority of the observed changes reached the maximum 1 mo after injury, whereas the effects evoked by spinal cord hemisection were significantly smaller and nearly constant in the studied period. The results of this study can be important for the prediction of changes in force regulation in human muscles after various extends of spinal cord injury and in evaluation of the frequency of functional electrical stimulation used for training of impaired muscles.
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Affiliation(s)
| | - Jan Celichowski
- Department of Neurobiology, University School of Physical Education, Poznań; and
| | - Piotr Krutki
- Department of Neurobiology, University School of Physical Education, Poznań; and
| | - Anna Cabaj
- Nencki Institute of Experimental Biology and
- Institute of Biocybernetics and Biomedical Engineering, Polish Academy of Sciences, Warsaw, Poland
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McGill KC, Marateb HR. Rigorous a posteriori assessment of accuracy in EMG decomposition. IEEE Trans Neural Syst Rehabil Eng 2010; 19:54-63. [PMID: 20639182 DOI: 10.1109/tnsre.2010.2056390] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
If electromyography (EMG) decomposition is to be a useful tool for scientific investigation, it is essential to know that the results are accurate. Because of background noise, waveform variability, motor-unit action potential (MUAP) indistinguishability, and perplexing superpositions, accuracy assessment is not straightforward. This paper presents a rigorous statistical method for assessing decomposition accuracy based only on evidence from the signal itself. The method uses statistical decision theory in a Bayesian framework to integrate all the shape- and firing-time-related information in the signal to compute an objective a posteriori measure of confidence in the accuracy of each discharge in the decomposition. The assessment is based on the estimated statistical properties of the MUAPs and noise and takes into account the relative likelihood of every other possible decomposition. The method was tested on 3 pairs of real EMG signals containing 4-7 active MUAP trains per signal that had been decomposed by a human expert. It rated 97% of the identified MUAP discharges as accurate to within ± 0.5 ms with a confidence level of 99%, and detected six decomposition errors. Cross-checking between signal pairs verified all but two of these assertions. These results demonstrate that the approach is reliable and practical for real EMG signals.
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Affiliation(s)
- Kevin C McGill
- Rehabilitation Research and Development Center, VA Palo Alto Health Care System, Palo Alto, CA 94304, USA.
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11
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Christie A, Greig Inglis J, Kamen G, Gabriel DA. Relationships between surface EMG variables and motor unit firing rates. Eur J Appl Physiol 2009; 107:177-85. [PMID: 19544067 DOI: 10.1007/s00421-009-1113-7] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/05/2009] [Indexed: 12/13/2022]
Abstract
Although surface electromyography (sEMG) is a widely used electrophysiological technique, its physiological interpretation remains somewhat controversial. This study examined the relationship between motor unit firing rates (MUFR) and the root mean square (RMS) amplitude and mean power frequency (MPF) of the sEMG signal in the biceps brachii. Eleven subjects performed maximal isometric elbow flexion while indwelling and sEMG recordings were obtained from the biceps. The RMS amplitude and MPF of the surface signal, and the mean MUFR from the indwelling signal, were calculated over 500 ms epochs. Group means showed a strong MUFR-RMS amplitude relationship (r (2) = 0.91), but a weak MUFR-MPF relationship (r (2) = 0.20). Using all trials, the MUFR-RMS amplitude (r (2) = 0.19) and MUFR-MPF (r (2) = 0.0037) relationships were much weaker. Within individual subjects, the MUFR-RMS amplitude (mean r (2) = 0.13 +/- 0.17) and the MUFR-MPF (mean r (2) = 0.040 +/- 0.041) relationships were also weak. These results suggest that MUFR cannot be predicted from the characteristics of the sEMG signal.
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Affiliation(s)
- Anita Christie
- Department of Kinesiology, University of Massachusetts, Amherst, MA, USA
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12
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Kesar T, Chou LW, Binder-Macleod SA. Effects of stimulation frequency versus pulse duration modulation on muscle fatigue. J Electromyogr Kinesiol 2007; 18:662-71. [PMID: 17317219 PMCID: PMC2562565 DOI: 10.1016/j.jelekin.2007.01.001] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2006] [Revised: 12/20/2006] [Accepted: 01/03/2007] [Indexed: 11/22/2022] Open
Abstract
During functional electrical stimulation (FES), both the frequency and intensity can be increased to increase muscle force output and counteract the effects of muscle fatigue. Most current FES systems, however, deliver a constant frequency and only vary the stimulation intensity to control muscle force. This study compared muscle performance and fatigue produced during repetitive electrical stimulation using three different strategies: (1) constant pulse-duration and stepwise increases in frequency (frequency-modulation); (2) constant frequency and stepwise increases in pulse-duration (pulse-duration-modulation); and (3) constant frequency and pulse-duration (no-modulation). Surface electrical stimulation was delivered to the quadriceps femoris muscles of 12 healthy individuals and isometric forces were recorded. Muscle performance was assessed by measuring the percent changes in the peak forces and force-time integrals between the first and the last fatiguing trains. Muscle fatigue was assessed by measuring percent declines in peak force between the 60Hz pre- and post-fatigue testing trains. The results showed that frequency-modulation showed better performance for both peak forces and force-time integrals in response to the fatiguing trains than pulse-duration-modulation, while producing similar levels of muscle fatigue. Although frequency-modulation is not commonly used during FES, clinicians should consider this strategy to improve muscle performance.
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Affiliation(s)
- Trisha Kesar
- Interdisciplinary Graduate Program in Biomechanics and Movement Science, Department of Physical Therapy, University of Delaware, Newark, DE, USA
| | - Li-Wei Chou
- Interdisciplinary Graduate Program in Biomechanics and Movement Science, Department of Physical Therapy, University of Delaware, Newark, DE, USA
| | - Stuart A. Binder-Macleod
- Interdisciplinary Graduate Program in Biomechanics and Movement Science, Department of Physical Therapy, University of Delaware, Newark, DE, USA
- Department of Physical Therapy, 301 McKinly Laboratory, University of Delaware, Newark, DE 19716, USA
- Corresponding author. Present address: Department of Physical Therapy, 301 McKinly Laboratory, University of Delaware, Newark, DE 19716, USA. Tel.: +1 302 831 8046. E-mail address: (S.A. Binder-Macleod)
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13
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Keogh J, Morrison S, Barrett R. Age-related differences in inter-digit coupling during finger pinching. Eur J Appl Physiol 2006; 97:76-88. [PMID: 16496196 DOI: 10.1007/s00421-006-0151-7] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/20/2006] [Indexed: 10/25/2022]
Abstract
The present study was designed to examine the finger-pinch force control, digit force sharing and digit coupling relations of 13 young and 14 older adults. Subjects performed four isometric tri-digit finger-pinch force production conditions reflecting all combinations of mean force level (20 and 40% MVC) and target shape (constant and sinusoidal). Older adults had significantly reduced force control, as indicated by their greater levels of absolute and relative force variability and targeting error than young adults. The age-related loss of relative force control was more pronounced at low (20% MVC) than high (40% MVC) forces, and to a lesser extent, in sinusoidal than constant force conditions. Older adults had significantly greater peak and proportional power below 1.5 Hz than young adults, with this especially pronounced in constant force conditions. Digit force sharing results indicated that the index finger's contribution to total force was increased and the middle finger's contribution reduced in older than young adults. The results of the cross-correlation analyses revealed that older subjects had a significantly reduced level of coupling between the middle finger and the target force, thumb force and EMG signals, with longer time lags in comparison to young adults. These differences in force sharing and middle finger force coupling were more pronounced in sinusoidal than constant force conditions. Overall, these results suggest that the older adults' reduced force control reflected age-related differences in the sharing and coupling of the finger forces. The results also highlighted that tasks of this nature display a degree of task-dependency, with these overall differences in digit force output and coupling not consistently observed across all force conditions.
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Affiliation(s)
- Justin Keogh
- Institute of Sport and Recreation Research New Zealand, Division of Sport and Recreation, Auckland University of Technology, Private Bag 92006, 1020, Auckland, New Zealand.
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Yahagi S, Takeda Y, Ni Z, Takahashi M, Tsuji T, Komiyama T, Maruishi M, Muranaka H, Kasai T. Modulations of input-output properties of corticospinal tract neurons by repetitive dynamic index finger abductions. Exp Brain Res 2004; 161:255-64. [PMID: 15502988 DOI: 10.1007/s00221-004-2059-y] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2004] [Accepted: 06/16/2004] [Indexed: 11/30/2022]
Abstract
The goal of this study was to investigate how corticospinal tract neurons (CTNs) are modulated after repetitive dynamic muscle contractions. To address this question, changes of motor evoked potentials (MEPs) to transcranial magnetic stimulation and background EMG (B.EMG) activities were examined. Subjects were instructed to perform an isometric dynamic index finger abduction as accurately as possible under the target-force-matching tasks (10% or 30% MVC), while MEPs of a first dorsal interosseous (FDI) were elicited during performance of the task. After repetitive dynamic FDI contractions (100 trials), the following remarkable phenomena were observed: (1) both B.EMG activities and MEP amplitudes decreased in proportion to the number of trials, (2) these phenomena were most commonly observed in different conditions, i.e., different force levels and hands (preferred or non-preferred hands), and (3) after repetition of the tasks, the MEP amplitude/B.EMG (MEP/B.EMG) ratio became smaller. Decreases of B.EMG activities with reduction of MEP amplitudes and diminishing MEP/B.EMG ratio might suggest the occurrence of reorganization of input-output properties in CTNs for an efficient performance as a function of motor adaptation. Thus, we conclude that motor adaptation after repetitive dynamic muscle contractions probably occurs less specifically and due to susceptible modulations of spinal motoneurons reflected in the integrative functions of CTNs.
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Affiliation(s)
- Susumu Yahagi
- Division of Sports and Health Sciences, Graduate School for International Development and Cooperation, Hiroshima University, 1717 Ohtsuka, Numata-cho, Asaminami-ku, Hiroshima, Japan
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McNulty PA, Cresswell AG. Recruitment of single human low-threshold motor units with increasing loads at different muscle lengths. J Electromyogr Kinesiol 2004; 14:369-77. [PMID: 15094150 DOI: 10.1016/j.jelekin.2003.10.003] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
We investigated the recruitment behaviour of low threshold motor units in flexor digitorum superficialis by altering two biomechanical constraints: the load against which the muscle worked and the initial muscle length. The load was increased using isotonic (low load), loaded dynamic (intermediate load) and isometric (high load) contractions in two studies. The initial muscle position reflected resting muscle length in series A, and a longer length with digit III fully extended in series B. Intramuscular EMG was recorded from 48 single motor units in 10 experiments on five healthy subjects, 21 units in series A and 27 in series B, while subjects performed ramp up, hold and ramp down contractions. Increasing the load on the muscle decreased the force, displacement and firing rate of single motor units at recruitment at shorter muscle lengths (P<0.001, dependent t-test). At longer muscle lengths this recruitment pattern was observed between loaded dynamic and isotonic contractions, but not between isometric and loaded dynamic contractions. Thus, the recruitment properties of single motor units in human flexor digitorum superficialis are sensitive to changes in both imposed external loads and the initial length of the muscle.
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Affiliation(s)
- P A McNulty
- Prince of Wales Medical Research Institute and University of New South Wales, Barker Street, Randwick, NSW 2031, Australia.
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Prather JF, Clark BD, Cope TC. Firing rate modulation of motoneurons activated by cutaneous and muscle receptor afferents in the decerebrate cat. J Neurophysiol 2002; 88:1867-79. [PMID: 12364513 DOI: 10.1152/jn.2002.88.4.1867] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The aim of this study was to investigate whether activation of spinal motoneurons by sensory afferents of the caudal cutaneous sural (CCS) nerve evokes an atypical motor control scheme. In this scheme, motor units that contract fast and forcefully are driven by CCS afferents to fire faster than motor units that contract more slowly and weakly. This is the opposite of the scheme described by the size principle. Earlier studies from this lab do not support the atypical scheme and instead demonstrate that both CCS and muscle stretch recruit motor units according to the size principle. The latter finding may indicate that CCS and muscle-stretch inputs have similar functional organizations or that comparison of recruitment sequence was simply unable to resolve a difference. In the present experiments, we examine this issue using rate modulation as a more sensitive index of motoneuron activation than recruitment. Quantification of the firing output generated by these two inputs in the same pairs of motoneurons enabled direct comparison of the functional arrangements of CCS versus muscle-stretch inputs across the pool of medial gastrocnemius (MG) motoneurons. No systematic difference was observed in the rate modulation produced by CCS versus muscle-stretch inputs for 35 pairs of MG motoneurons. For the subset of 24 motoneuron pairs exhibiting linear co-modulation of firing rate (r > 0.5) in response to both CCS and muscle inputs, the slopes of the regression lines were statistically indistinguishable between the two inputs. For individual motoneuron pairs, small differences in slope between inputs were not related to differences in conduction velocity (CV), recruitment order, or, for a small sample, differences in motor unit force. We conclude that an atypical motor control scheme involving selective activation of typically less excitable motoneurons, if it does occur during normal movement, is not an obligatory consequence of activation by sural nerve afferents. On average and for both muscle-stretch and skin-pinch inputs, the motoneuron with the faster CV in the pair tended to be driven to fire at slightly but significantly faster firing rates. Computer simulations based in part on frequency-current relations measured directly from motoneurons revealed that properties intrinsic to motoneurons are sufficient to account for the higher firing rates of the faster CV motoneuron in a pair.
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Affiliation(s)
- J F Prather
- Department of Physiology, Emory University, Atlanta, Georgia 30322, USA.
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