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Olmos AA, Sontag SA, Sterczala AJ, Parra ME, Dimmick HL, Miller JD, Deckert JA, Herda TJ, Trevino MA. High-Intensity Cycling Training Necessitates Increased Neuromuscular Demand of the Vastus Lateralis During a Fatiguing Contraction. RESEARCH QUARTERLY FOR EXERCISE AND SPORT 2024; 95:313-324. [PMID: 37369135 DOI: 10.1080/02701367.2023.2201311] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2022] [Accepted: 04/05/2023] [Indexed: 06/29/2023]
Abstract
Purpose: To examine the effects of a 5-week continuous cycling training intervention on electromyographic amplitude (EMGRMS)- and mechanomyographic amplitude (MMGRMS)-torque relationships of the vastus lateralis (VL) during a prolonged contraction. Methods: Twenty-four sedentary, young adults performed maximal voluntary contractions (MVCs) and a prolonged isometric trapezoidal contraction at the same absolute 40% MVC for the knee extensors before (PRE) and after training (POSTABS). Individual b- (slopes) and a-terms (y-intercepts) were calculated from the log-transformed electromyographic amplitude (EMGRMS)- and mechanomyographic amplitude (MMGRMS)-torque relationships during the increasing and decreasing segments of the trapezoid. EMGRMS and MMGRMS was normalized for the 45-s steady torque segment. Results: At PRE, b-terms for the EMGRMS-torque relationships during the linearly decreasing segment were greater than the increasing segment (p < .001), and decreased from PRE to POSTABS (p = .027). a-terms were greater during the linearly increasing than decreasing segment at PRE, while the a-terms for the linearly decreasing segment increased from PRE to POSTABS (p = .027). For the MMGRMS-torque relationships, b-terms during the linearly decreasing segment decreased from PRE to POSTABS (p = .013), while a-terms increased from PRE to POSTABS when collapsed across segments (p = .022). Steady torque EMGRMS increased for POSTABS (p < .001). Conclusion: Although cycling training increased aerobic endurance, incorporating resistance training may benefit athletes/individuals as the alterations in neuromuscular parameters post-training suggest a greater neural cost (EMGRMS) and mechanical output (MMGRMS) to complete the same pre-training fatiguing contraction.
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Valenčič T, Ansdell P, Brownstein CG, Spillane PM, Holobar A, Škarabot J. Motor unit discharge rate modulation during isometric contractions to failure is intensity- and modality-dependent. J Physiol 2024; 602:2287-2314. [PMID: 38619366 DOI: 10.1113/jp286143] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2023] [Accepted: 03/25/2024] [Indexed: 04/16/2024] Open
Abstract
The physiological mechanisms determining the progressive decline in the maximal muscle torque production capacity during isometric contractions to task failure are known to depend on task demands. Task-specificity of the associated adjustments in motor unit discharge rate (MUDR), however, remains unclear. This study examined MUDR adjustments during different submaximal isometric knee extension tasks to failure. Participants performed a sustained and an intermittent task at 20% and 50% of maximal voluntary torque (MVT), respectively (Experiment 1). High-density surface EMG signals were recorded from vastus lateralis (VL) and medialis (VM) and decomposed into individual MU discharge timings, with the identified MUs tracked from recruitment to task failure. MUDR was quantified and normalised to intervals of 10% of contraction time (CT). MUDR of both muscles exhibited distinct modulation patterns in each task. During the 20% MVT sustained task, MUDR decreased until ∼50% CT, after which it gradually returned to baseline. Conversely, during the 50% MVT intermittent task, MUDR remained stable until ∼40-50% CT, after which it started to continually increase until task failure. To explore the effect of contraction intensity on the observed patterns, VL and VM MUDR was quantified during sustained contractions at 30% and 50% MVT (Experiment 2). During the 30% MVT sustained task, MUDR remained stable until ∼80-90% CT in both muscles, after which it continually increased until task failure. During the 50% MVT sustained task the increase in MUDR occurred earlier, after ∼70-80% CT. Our results suggest that adjustments in MUDR during submaximal isometric contractions to failure are contraction modality- and intensity-dependent. KEY POINTS: During prolonged muscle contractions a constant motor output can be maintained by recruitment of additional motor units and adjustments in their discharge rate. Whilst contraction-induced decrements in neuromuscular function are known to depend on task demands, task-specificity of motor unit discharge behaviour adjustments is still unclear. In this study, we tracked and compared discharge activity of several concurrently active motor units in the vastii muscles during different submaximal isometric knee extension tasks to failure, including intermittent vs. sustained contraction modalities performed in the same intensity domain (Experiment 1), and two sustained contractions performed at different intensities (Experiment 2). During each task, motor units modulated their discharge rate in a distinct, biphasic manner, with the modulation pattern depending on contraction intensity and modality. These results provide insight into motoneuronal adjustments during contraction tasks posing different demands on the neuromuscular system.
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Affiliation(s)
- Tamara Valenčič
- School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, UK
| | - Paul Ansdell
- Department of Sport, Exercise and Rehabilitation, Northumbria University, Newcastle upon Tyne, UK
| | - Callum G Brownstein
- School of Biomedical, Nutritional and Sport Sciences, Newcastle University, Newcastle upon Tyne, UK
| | - Padraig M Spillane
- Department of Sport, Exercise and Rehabilitation, Northumbria University, Newcastle upon Tyne, UK
| | - Aleš Holobar
- Faculty of Electrical Engineering and Computer Science, University of Maribor, Maribor, Slovenia
| | - Jakob Škarabot
- School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, UK
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Nishikawa T, Takeda R, Hirono T, Okudaira M, Ohya T, Watanabe K. Differences in acute neuromuscular response after single session of resistance exercise between young and older adults. Exp Gerontol 2024; 185:112346. [PMID: 38104744 DOI: 10.1016/j.exger.2023.112346] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2023] [Revised: 12/07/2023] [Accepted: 12/10/2023] [Indexed: 12/19/2023]
Abstract
AIMS The purpose of this study was to investigate differences in the acute response after resistance exercise between young and older adults. METHODS Seventeen young and 18 older adults performed a single session of resistance exercise, consisting of 3 sets of 10 isometric knee extensions. Maximal voluntary contraction (MVC), motor unit (MU) activity of the vastus lateralis, and electrically elicited torque of the knee extensor were measured before and after the resistance exercise. RESULTS Although both groups showed the same degree of decline in MVC (young: -15.2 ± 14.3 %, older: -16.4 ± 7.9 %, p = 0.839), electrically elicited torque markedly decreased in the young group (young: -21.5 ± 7.7 %, older: -14.3 ± 9.5 %, p < 0.001), and the decrease in the MU firing rate was greater in the older group (young: -26.1 ± 24.1 %, older: -44.7 ± 24.5 %, p < 0.001). Changes in the MU firing rate following the exercise were correlated with the MU recruitment threshold in the older group (p < 0.001, rs = 0.457), but not young group (p = 0.960). DISCUSSION These results showed that young adults exhibited a greater acute response in the peripheral component, whereas older adults showed a greater acute response in the central component of the neuromuscular system, and the acute response in MUs with a high recruitment threshold following resistance exercise was smaller than in those with a low recruitment threshold in older adults. These findings may partly explain why there are different chronic adaptations to resistance training between young and older adults.
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Affiliation(s)
- Taichi Nishikawa
- Graduate School of Health and Sport Sciences, Chukyo University, Toyota, Japan; Laboratory of Neuromuscular Biomechanics, School of Health and Sport Sciences, Chukyo University, Toyota, Japan
| | - Ryosuke Takeda
- Laboratory of Neuromuscular Biomechanics, School of Health and Sport Sciences, Chukyo University, Toyota, Japan
| | - Tetsuya Hirono
- Laboratory of Neuromuscular Biomechanics, School of Health and Sport Sciences, Chukyo University, Toyota, Japan; Research Fellow of Japan Society for the Promotion of Science, Tokyo, Japan
| | - Masamichi Okudaira
- Laboratory of Neuromuscular Biomechanics, School of Health and Sport Sciences, Chukyo University, Toyota, Japan; Faculty of Education, Iwate University, Iwate, Japan
| | - Toshiyuki Ohya
- Laboratory for Exercise Physiology and Biomechanics, Graduate School of Health and Sport Sciences, Chukyo University, Toyota, Japan
| | - Kohei Watanabe
- Laboratory of Neuromuscular Biomechanics, School of Health and Sport Sciences, Chukyo University, Toyota, Japan.
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Carvalho CR, Fernández JM, Del-Ama AJ, Oliveira Barroso F, Moreno JC. Review of electromyography onset detection methods for real-time control of robotic exoskeletons. J Neuroeng Rehabil 2023; 20:141. [PMID: 37872633 PMCID: PMC10594734 DOI: 10.1186/s12984-023-01268-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2022] [Accepted: 10/13/2023] [Indexed: 10/25/2023] Open
Abstract
BACKGROUND Electromyography (EMG) is a classical technique used to record electrical activity associated with muscle contraction and is widely applied in Biomechanics, Biomedical Engineering, Neuroscience and Rehabilitation Robotics. Determining muscle activation onset timing, which can be used to infer movement intention and trigger prostheses and robotic exoskeletons, is still a big challenge. The main goal of this paper was to perform a review of the state-of-the-art of EMG onset detection methods. Moreover, we compared the performance of the most commonly used methods on experimental EMG data. METHODS A total of 156 papers published until March 2022 were included in the review. The papers were analyzed in terms of application domain, pre-processing method and EMG onset detection method. The three most commonly used methods [Single (ST), Double (DT) and Adaptive Threshold (AT)] were applied offline on experimental intramuscular and surface EMG signals obtained during contractions of ankle and knee joint muscles. RESULTS Threshold-based methods are still the most commonly used to detect EMG onset. Compared to ST and AT, DT required more processing time and, therefore, increased onset timing detection, when applied on experimental data. The accuracy of these three methods was high (maximum error detection rate of 7.3%), demonstrating their ability to automatically detect the onset of muscle activity. Recently, other studies have tested different methods (especially Machine Learning based) to determine muscle activation onset offline, reporting promising results. CONCLUSIONS This study organized and classified the existing EMG onset detection methods to create consensus towards a possible standardized method for EMG onset detection, which would also allow more reproducibility across studies. The three most commonly used methods (ST, DT and AT) proved to be accurate, while ST and AT were faster in terms of EMG onset detection time, especially when applied on intramuscular EMG data. These are important features towards movement intention identification, especially in real-time applications. Machine Learning methods have received increased attention as an alternative to detect muscle activation onset. However, although several methods have shown their capability offline, more research is required to address their full potential towards real-time applications, namely to infer movement intention.
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Affiliation(s)
- Camila R Carvalho
- Neural Rehabilitation Group, Cajal Institute, Spanish National Research Council (CSIC), Madrid, Spain
| | - J Marvin Fernández
- Electronic Technology Department, Rey Juan Carlos University, Madrid, Spain
| | - Antonio J Del-Ama
- Electronic Technology Department, Rey Juan Carlos University, Madrid, Spain
| | - Filipe Oliveira Barroso
- Neural Rehabilitation Group, Cajal Institute, Spanish National Research Council (CSIC), Madrid, Spain.
| | - Juan C Moreno
- Neural Rehabilitation Group, Cajal Institute, Spanish National Research Council (CSIC), Madrid, Spain
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Balinski M, Madhavan S. "Magic" Number of Treadmill Sessions Needed to Achieve Meaningful Change in Gait Speed After Stroke: A Systematic Review. Am J Phys Med Rehabil 2022; 101:826-835. [PMID: 34799509 PMCID: PMC9108112 DOI: 10.1097/phm.0000000000001920] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
ABSTRACT The purpose of this systematic review was to determine the number of treadmill training sessions needed to make a meaningful change in gait speed for chronic stroke survivors. Relevant databases were searched up through February 2020. Articles were included if they fit the following criteria: stroke onset more than 5 mos, intention to treat with traditional treadmill training, and gait speed included as an outcome. Change in gait speed after intervention was used to classify treadmill groups as responders (at least 0.1 m/sec change) or nonresponders (less than 0.1 m/sec change). Seventeen articles met our criteria, resulting in a total of 19 intervention groups. Ten groups were classified as responders and completed a mean of 30.5 sessions within 6 wks, whereas nonresponders completed 20.4 sessions within 10 wks, indicating that at least 30 treadmill sessions (preferably in a period of 10 wks and at least 40 mins per session) is necessary to reach a meaningful change in gait speed. Although these trends were noted between the responder and nonresponder groups, no firm conclusions can be drawn regarding the "magic" number of sessions chronic stroke survivors should perform given the low correlation between number of sessions and change in gait speed.
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Affiliation(s)
- Mariah Balinski
- Brain Plasticity Lab, Department of Physical Therapy, College of Applied Health Sciences, University of Illinois at Chicago, Chicago, IL, USA
- Graduate Program in Rehabilitation Science, College of Applied Health Sciences, University of Illinois, Chicago, IL, USA
| | - Sangeetha Madhavan
- Brain Plasticity Lab, Department of Physical Therapy, College of Applied Health Sciences, University of Illinois at Chicago, Chicago, IL, USA
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Resistance exercise training and the motor unit. Eur J Appl Physiol 2022; 122:2019-2035. [PMID: 35751668 DOI: 10.1007/s00421-022-04983-7] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2022] [Accepted: 06/06/2022] [Indexed: 11/03/2022]
Abstract
Resistance exercise training (RET) is a key modality to enhance sports performance, injury prevention and rehabilitation, and improving overall health via increases in muscular strength. Yet, the contribution of neural mechanisms to increases in muscular strength are highly debated. This is particularly true for the involvement of the motor unit, which is the link between neural (activation) and mechanical (muscle fiber twitch forces) mechanisms. A plethora of literature that examines the effects of RET on skeletal muscle speculate the role of motor units, such as increases in firing rates partially explains muscular strength gains. Results, however, are mixed regarding changes in firing rates in studies that utilize single motor unit recordings. The lack of clarity could be related to vast or subtle differences in RET programs, methods to record motor units, muscles tested, types of contractions and intensities used to record motor units, etc. Yet to be discussed, mixed findings could be the result of non-uniform MU behavior that is not typically accounted for in RET research. The purpose of this narration is to discuss the effects of acute resistance exercise training studies on MU behavior and to provide guidance for future research.
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Rossato J, Tucker KJ, Avrillon S, Lacourpaille L, Holobar A, Hug F. Less common synaptic input between muscles from the same group allows for more flexible coordination strategies during a fatiguing task. J Neurophysiol 2022; 127:421-433. [PMID: 35020505 DOI: 10.1152/jn.00453.2021] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
This study aimed to determine whether neural drive is redistributed between muscles during a fatiguing isometric contraction, and if so, whether the initial level of common synaptic input between these muscles constrains this redistribution. We studied two muscle groups: triceps surae (14 participants) and quadriceps (15 participants). Participants performed a series of submaximal isometric contractions and a torque-matched contraction maintained until task failure. We used high-density surface electromyography to identify the behavior of 1874 motor units from the soleus, gastrocnemius medialis (GM), gastrocnemius lateralis(GL), rectus femoris, vastus lateralis (VL), and vastus medialis(VM). We assessed the level of common drive between muscles in absence of fatigue using a coherence analysis. We also assessed the redistribution of neural drive between muscles during the fatiguing contraction through the correlation between their cumulative spike trains (index of neural drive). The level of common drive between VL and VM was significantly higher than that observed for the other muscle pairs, including GL-GM. The level of common drive increased during the fatiguing contraction, but the differences between muscle pairs persisted. We also observed a strong positive correlation of neural drive between VL and VM during the fatiguing contraction (r=0.82). This was not observed for the other muscle pairs, including GL-GM, which exhibited differential changes in neural drive. These results suggest that less common synaptic input between muscles allows for more flexible coordination strategies during a fatiguing task, i.e., differential changes in neural drive across muscles. The role of this flexibility on performance remains to be elucidated.
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Affiliation(s)
- Julien Rossato
- Nantes Université, Laboratory "Movement, Interactions, Performance" (EA 4334), Nantes, France
| | - Kylie J Tucker
- The University of Queensland, School of Biomedical Sciences, Brisbane, Queensland, Australia
| | - Simon Avrillon
- Legs + Walking AbilityLab, Shirley Ryan AbilityLab, Chicago, IL, United States.,Department of Physical Medicine and Rehabilitation, Northwestern University, Chicago, IL, United States
| | - Lilian Lacourpaille
- Nantes Université, Laboratory "Movement, Interactions, Performance" (EA 4334), Nantes, France
| | - Ales Holobar
- Faculty of Electrical Engineering and Computer Science, University of Maribor, Slovenia
| | - François Hug
- Nantes Université, Laboratory "Movement, Interactions, Performance" (EA 4334), Nantes, France.,Institut Universitaire de France (IUF), Paris, France.,Université Côte d'Azur, LAMHESS, Nice, France
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Christou GA, Pagourelias ED, Deligiannis AP, Kouidi EJ. Exploring the Anthropometric, Cardiorespiratory, and Haematological Determinants of Marathon Performance. Front Physiol 2021; 12:693733. [PMID: 34539429 PMCID: PMC8446630 DOI: 10.3389/fphys.2021.693733] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2021] [Accepted: 08/11/2021] [Indexed: 11/13/2022] Open
Abstract
Aim We aimed to investigate the main anthropometric, cardiorespiratory and haematological factors that can determine marathon race performance in marathon runners. Methods Forty-five marathon runners (36 males, age: 42 ± 10 years) were examined during the training period for a marathon race. Assessment of training characteristics, anthropometric measurements, including height, body weight (n = 45) and body fat percentage (BF%) (n = 33), echocardiographic study (n = 45), cardiopulmonary exercise testing using treadmill ergometer (n = 33) and blood test (n = 24) were performed. We evaluated the relationships of these measurements with the personal best marathon race time (MRT) within a time frame of one year before or after the evaluation of each athlete. Results The training age regarding long-distance running was 9 ± 7 years. Training volume was 70 (50-175) km/week. MRT was 4:02:53 ± 00:50:20 h. The MRT was positively associated with BF% (r = 0.587, p = 0.001). Among echocardiographic parameters, MRT correlated negatively with right ventricular end-diastolic area (RVEDA) (r = -0.716, p < 0.001). RVEDA was the only independent echocardiographic predictor of MRT. With regard to respiratory parameters, MRT correlated negatively with maximum minute ventilation indexed to body surface area (VEmax/BSA) (r = -0.509, p = 0.003). Among parameters of blood test, MRT correlated negatively with haemoglobin concentration (r = -0.471, p = 0.027) and estimated haemoglobin mass (Hbmass) (r = -0.680, p = 0.002). After performing multivariate linear regression analysis with MRT as dependent variable and BF% (standardised β = 0.501, p = 0.021), RVEDA (standardised β = -0.633, p = 0.003), VEmax/BSA (standardised β = 0.266, p = 0.303) and Hbmass (standardised β = -0.308, p = 0.066) as independent variables, only BF% and RVEDA were significant independent predictors of MRT (adjusted R2 = 0.796, p < 0.001 for the model). Conclusions The main physiological determinants of better marathon performance appear to be low BF% and RV enlargement. Upregulation of both maximum minute ventilation during exercise and haemoglobin mass may have a weaker effect to enhance marathon performance. Clinical Trial Registration www.ClinicalTrials.gov, identifier NCT04738877.
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Affiliation(s)
- Georgios A Christou
- Laboratory of Sports Medicine, Sports Medicine Division, Aristotle University of Thessaloniki, Thessaloniki, Greece
| | - Efstathios D Pagourelias
- Laboratory of Sports Medicine, Sports Medicine Division, Aristotle University of Thessaloniki, Thessaloniki, Greece
| | - Asterios P Deligiannis
- Laboratory of Sports Medicine, Sports Medicine Division, Aristotle University of Thessaloniki, Thessaloniki, Greece
| | - Evangelia J Kouidi
- Laboratory of Sports Medicine, Sports Medicine Division, Aristotle University of Thessaloniki, Thessaloniki, Greece
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The Effects of Spinal Manipulation on Motor Unit Behavior. Brain Sci 2021; 11:brainsci11010105. [PMID: 33466707 PMCID: PMC7828823 DOI: 10.3390/brainsci11010105] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2020] [Revised: 01/08/2021] [Accepted: 01/12/2021] [Indexed: 12/05/2022] Open
Abstract
Over recent years, a growing body of research has highlighted the neural plastic effects of spinal manipulation on the central nervous system. Recently, it has been shown that spinal manipulation improved outcomes, such as maximum voluntary force and limb joint position sense, reflecting improved sensorimotor integration and processing. This study aimed to further evaluate how spinal manipulation can alter neuromuscular activity. High density electromyography (HD sEMG) signals from the tibialis anterior were recorded and decomposed in order to study motor unit changes in 14 subjects following spinal manipulation or a passive movement control session in a crossover study design. Participants were asked to produce ankle dorsiflexion at two force levels, 5% and 10% of maximum voluntary contraction (MVC), following two different patterns of force production (“ramp” and “ramp and maintain”). A significant decrease in the conduction velocity (p = 0.01) was observed during the “ramp and maintain” condition at 5% MVC after spinal manipulation. A decrease in conduction velocity suggests that spinal manipulation alters motor unit recruitment patterns with an increased recruitment of lower threshold, lower twitch torque motor units.
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Niazi IK, Kamavuako EN, Holt K, Janjua TAM, Kumari N, Amjad I, Haavik H. The Effect of Spinal Manipulation on the Electrophysiological and Metabolic Properties of the Tibialis Anterior Muscle. Healthcare (Basel) 2020; 8:healthcare8040548. [PMID: 33321904 PMCID: PMC7764559 DOI: 10.3390/healthcare8040548] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2020] [Revised: 12/07/2020] [Accepted: 12/07/2020] [Indexed: 12/31/2022] Open
Abstract
There is growing evidence showing that spinal manipulation increases muscle strength in healthy individuals as well as in people with some musculoskeletal and neurological disorders. However, the underlying mechanism by which spinal manipulation changes muscle strength is less clear. This study aimed to assess the effects of a single spinal manipulation session on the electrophysiological and metabolic properties of the tibialis anterior (TA) muscle. Maximum voluntary contractions (MVC) of the ankle dorsiflexors, high-density electromyography (HDsEMG), intramuscular EMG, and near-infrared spectroscopy (NIRS) were recorded from the TA muscle in 25 participants with low level recurring spinal dysfunction using a randomized controlled crossover design. The following outcomes: motor unit discharge rate (MUDR), strength (force at MVC), muscle conduction velocity (CV), relative changes in oxy- and deoxyhemoglobin were assessed pre and post a spinal manipulation intervention and passive movement control. Repeated measures ANOVA was used to assess within and between-group differences. Following the spinal manipulation intervention, there was a significant increase in MVC (p = 0.02; avg 18.87 ± 28.35%) and a significant increase in CV in both the isometric steady-state (10% of MVC) contractions (p < 0.01; avg 22.11 ± 11.69%) and during the isometric ramp (10% of MVC) contractions (p < 0.01; avg 4.52 ± 4.58%) compared to the control intervention. There were no other significant findings. The observed TA strength and CV increase, without changes in MUDR, suggests that the strength changes observed following spinal manipulation are, in part, due to increased recruitment of larger, higher threshold motor units. Further research needs to investigate the longer term and potential functional effects of spinal manipulation in various patients who may benefit from improved muscle function and greater motor unit recruitment.
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Affiliation(s)
- Imran Khan Niazi
- Centre for Chiropractic Research, New Zealand College of Chiropractic, Auckland 1060, New Zealand; (K.H.); (N.K.); (I.A.)
- Faculty of Health & Environmental Sciences, Health & Rehabilitation Research Institute, AUT University, Auckland 0627, New Zealand
- Department of Health Science and Technology, Aalborg University, Aalborg 9220, Denmark;
- Correspondence: (I.K.N.); (H.H.)
| | - Ernest Nlandu Kamavuako
- Department of Informatics, King’s College London, London WC2R 2LS, UK;
- Faculté de Médecine, Université de Kindu, Kindu, Congo
| | - Kelly Holt
- Centre for Chiropractic Research, New Zealand College of Chiropractic, Auckland 1060, New Zealand; (K.H.); (N.K.); (I.A.)
| | | | - Nitika Kumari
- Centre for Chiropractic Research, New Zealand College of Chiropractic, Auckland 1060, New Zealand; (K.H.); (N.K.); (I.A.)
- Faculty of Health & Environmental Sciences, Health & Rehabilitation Research Institute, AUT University, Auckland 0627, New Zealand
| | - Imran Amjad
- Centre for Chiropractic Research, New Zealand College of Chiropractic, Auckland 1060, New Zealand; (K.H.); (N.K.); (I.A.)
- Faculty of Rehabilitation and Allied Sciences, Riphah International University, Islamabad 46000, Pakistan
| | - Heidi Haavik
- Centre for Chiropractic Research, New Zealand College of Chiropractic, Auckland 1060, New Zealand; (K.H.); (N.K.); (I.A.)
- Correspondence: (I.K.N.); (H.H.)
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Barreto RV, de Lima LCR, Denadai BS. Moving forward with backward pedaling: a review on eccentric cycling. Eur J Appl Physiol 2020; 121:381-407. [PMID: 33180156 DOI: 10.1007/s00421-020-04548-6] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2020] [Accepted: 10/31/2020] [Indexed: 12/18/2022]
Abstract
PURPOSE There is a profound gap in the understanding of the eccentric cycling intensity continuum, which prevents accurate exercise prescription based on desired physiological responses. This may underestimate the applicability of eccentric cycling for different training purposes. Thus, we aimed to summarize recent research findings and screen for possible new approaches in the prescription and investigation of eccentric cycling. METHOD A search for the most relevant and state-of-the-art literature on eccentric cycling was conducted on the PubMed database. Literature from reference lists was also included when relevant. RESULTS Transversal studies present comparisons between physiological responses to eccentric and concentric cycling, performed at the same absolute power output or metabolic load. Longitudinal studies evaluate responses to eccentric cycling training by comparing them with concentric cycling and resistance training outcomes. Only one study investigated maximal eccentric cycling capacity and there are no investigations on physiological thresholds and/or exercise intensity domains during eccentric cycling. No study investigated different protocols of eccentric cycling training and the chronic effects of different load configurations. CONCLUSION Describing physiological responses to eccentric cycling based on its maximal exercise capacity may be a better way to understand it. The available evidence indicates that clinical populations may benefit from improvements in aerobic power/capacity, exercise tolerance, strength and muscle mass, while healthy and trained individuals may require different eccentric cycling training approaches to benefit from similar improvements. There is limited evidence regarding the mechanisms of acute physiological and chronic adaptive responses to eccentric cycling.
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Affiliation(s)
- Renan Vieira Barreto
- Human Performance Laboratory, Department of Physical Education, São Paulo State University, Rio Claro, São Paulo, Brazil
| | | | - Benedito Sérgio Denadai
- Human Performance Laboratory, Department of Physical Education, São Paulo State University, Rio Claro, São Paulo, Brazil.
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Miller JD, Lippman JD, Trevino MA, Herda TJ. Neural Drive is Greater for a High-Intensity Contraction Than for Moderate-Intensity Contractions Performed to Fatigue. J Strength Cond Res 2020; 34:3013-3021. [PMID: 33105349 DOI: 10.1519/jsc.0000000000003694] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/13/2023]
Abstract
Miller, JD, Lippman, JD, Trevino, MA, and Herda, TJ. Larger motor units are recruited for high-intensity contractions than for fatiguing moderate-intensity contractions. J Strength Cond Res 34(11): 3013-3021, 2020-The purpose of this study was to investigate whether moderate-intensity contractions performed to fatigue activate the motor unit (MU) pool to the same extent as a higher-intensity contraction. Subjects (7 men, 2 women, age = 22.78 ± 4.15 years, height = 173.78 ± 14.19 cm, mass = 87.39 ± 21.19 kg) performed 3 isometric maximum voluntary contractions (MVCs), an isometric trapezoidal contraction at 90% MVC (REP90), and repetitive isometric trapezoidal contractions at 50% MVC performed to failure with the first (REP1) and final repetition (REPL) used for analysis. Surface EMG was recorded from the vastus lateralis. Action potentials were extracted into firing events of single MUs with recruitment thresholds (RTs), MU action potential amplitudes (MUAPAMP), and mean firing rates (MFRs) recorded. Linear MFR and MUAPAMP vs. RT and exponential MFR vs. MUAPAMP relationships were calculated for each subject. The level of significance was set at p ≤ 0.05. B terms for the MFR vs. MUAPAMP relationships (p = 0.001, REPL = -4.77 ± 1.82 pps·mV, REP90 = -2.63 ± 1.00 pps·mV) and predicted MFRs for MUs recruited at 40% MVC (p < 0.001, REPL = 11.14 ± 3.48 pps, REP90 = 18.38 ± 2.60 pps) were greater for REP90 than REPL indicating firing rates were greater during REP90. In addition, larger mean (p = 0.038, REPL = 0.178 ± 0.0668 mV, REP90 = 0.263 ± 0.128 mV) and maximum (p = 0.008, REPL = 0.320 ± 0.127 mV, Rep90 = 0.520 ± 0.234 mV) MUAPAMPS were recorded during REP90 than REPL. Larger MUs were recruited and similar sized MUs maintained greater firing rates during a high-intensity contraction in comparison to a moderate-intensity contraction performed at fatigue. Individuals seeking maximized activation of the MU pool should use high-intensity resistance training paradigms rather than moderate-intensity to fatigue.
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Affiliation(s)
- Jonathan D Miller
- Neuromechanics Laboratory, Department of Health, Sport and Exercise Sciences, University of Kansas, Lawrence, Kansas; and
| | - Jeremy D Lippman
- Neuromechanics Laboratory, Department of Health, Sport and Exercise Sciences, University of Kansas, Lawrence, Kansas; and
| | - Michael A Trevino
- Applied Neuromuscular Physiology Laboratory, Department of Health and Human Performance, Oklahoma State University, Stillwater, Oklahoma
| | - Trent J Herda
- Neuromechanics Laboratory, Department of Health, Sport and Exercise Sciences, University of Kansas, Lawrence, Kansas; and
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Mota JA, Kwon DP, Kennedy M, Sobolewski EJ, Kim Y, Gonzales JU, Stock MS. Compensatory adjustments in motor unit behavior during fatigue differ for younger versus older men. Aging Clin Exp Res 2020; 32:2259-2269. [PMID: 31898169 DOI: 10.1007/s40520-019-01438-6] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2019] [Accepted: 12/03/2019] [Indexed: 10/25/2022]
Abstract
BACKGROUND The ability to maintain a submaximal force as a muscle fatigues is supplemented by compensatory adjustments in the nervous system's control of motor units. AIM We sought to compare vastus lateralis motor unit recruitment and firing rate data for younger versus older men during isometric fatigue. METHODS Twelve younger (age = 25 ± 3 years) and 12 older (75 ± 8 years) men performed contractions of the knee extensors at 50% of maximal voluntary contraction force until exhaustion. Surface electromyographic (sEMG) signals were detected from the vastus lateralis. A sEMG signal decomposition algorithm was used to quantify the motor unit action potential (MUAP) amplitude, mean firing rates, and recruitment threshold of each motor unit. For the latter two variables, our analyses only included motor units that featured similar action potential amplitude throughout the protocol. RESULTS There was no group difference for time to task failure (p = 0.362, d = 0.381). Both groups showed increases in MUAP amplitude [younger and older slopes = 0.0174 ± 0.0123 and 0.0073 ± 0.0123 mV/contraction, respectively (p = 0.082, d = 0.710)], but the change was more linear for the younger men (mean r2 values = 0.565 and 0.455). Mean firing rates increased over time for the younger (p < 0.001), but not the older (p = 0.579), men. Similarly, recruitment thresholds decreased for younger men (p = 0.001). CONCLUSION We propose that aging results in neuromuscular impairments that hinder older adults' ability to make compensatory adjustments in motor unit control during fatigue.
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Martinez-Valdes E, Negro F, Falla D, Dideriksen JL, Heckman CJ, Farina D. Inability to increase the neural drive to muscle is associated with task failure during submaximal contractions. J Neurophysiol 2020; 124:1110-1121. [DOI: 10.1152/jn.00447.2020] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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.
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Affiliation(s)
- Eduardo Martinez-Valdes
- Centre of Precision Rehabilitation for Spinal Pain (CPR Spine), School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Francesco Negro
- Department of Clinical and Experimental Sciences, Research Centre for Neuromuscular Function and Adapted Physical Activity “Teresa Camplani,” Università degli Studi di Brescia, Brescia, Italy
| | - Deborah Falla
- Centre of Precision Rehabilitation for Spinal Pain (CPR Spine), School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Jakob Lund Dideriksen
- Center for Sensory-Motor Interaction, Department of Health Science and Technology, Aalborg University, Aalborg, Denmark
| | - C. J. Heckman
- Department of Physiology, Northwestern University, Chicago, Illinois
| | - Dario Farina
- Department of Bioengineering, Imperial College London, Royal School of Mines, London, United Kingdom
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15
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Watanabe K, Holobar A, Tomita A, Mita Y. Effect of milk fat globule membrane supplementation on motor unit adaptation following resistance training in older adults. Physiol Rep 2020; 8:e14491. [PMID: 32597035 PMCID: PMC7322501 DOI: 10.14814/phy2.14491] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2020] [Accepted: 05/24/2020] [Indexed: 11/24/2022] Open
Abstract
This study aimed to investigate the effect of milk fat globule membrane (MFGM) supplementation on motor unit adaptation following resistance training in older adults. Twenty-five older males and females took MFGM (n = 12) or a placebo (PLA; n = 12) while performing 8 weeks of isometric knee extension training. During the training, the motor unit firing pattern during submaximal contractions, muscle thickness, and maximal muscle strength of knee extensor muscles were measured every 2 weeks. None of the measurements showed significant differences in muscle thickness or maximal muscle strength (MVC) between the two groups (p > .05). Significant decreases in motor unit firing rate following the intervention were observed in PLA, that is, 14.1 ± 2.7 pps at 0 weeks to 13.0 ± 2.4 pps at 4 weeks (p = .003), but not in MFGM (14.4 ± 2.5 pps to 13.8 ± 1.9 pps). Motor unit firing rates in MFGM were significantly higher than those in PLA at 2, 4, 6, and 8 weeks of the intervention, that is, 15.1 ± 2.3 pps in MFGM and 14.5 ± 3.3 pps in PLA at 70% of MVC for motor units recruited at 40% of MVC at 6 weeks (p = .034). Significant differences in firing rates among motor units with different recruitment thresholds were newly observed following the resistance training intervention in MFGM, indicating that motor unit firing pattern is changed in this group. These results suggest that motor unit adaptation following resistance training is modulated by MFGM supplementation in older adults.
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Affiliation(s)
- Kohei Watanabe
- Laboratory of Neuromuscular BiomechanicsSchool of International Liberal StudiesChukyo UniversityNagoyaJapan
| | - Aleš Holobar
- Faculty of Electrical Engineering and Computer ScienceUniversity of MariborMariborSlovenia
| | - Aya Tomita
- Laboratory of Neuromuscular BiomechanicsSchool of International Liberal StudiesChukyo UniversityNagoyaJapan
| | - Yukiko Mita
- Department of Human NutritionSchool of Life StudiesSugiyama Jogakuen UniversityNagoyaJapan
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16
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Enoka RM. Physiological validation of the decomposition of surface EMG signals. J Electromyogr Kinesiol 2019; 46:70-83. [PMID: 31003192 DOI: 10.1016/j.jelekin.2019.03.010] [Citation(s) in RCA: 46] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2018] [Revised: 02/15/2019] [Accepted: 03/20/2019] [Indexed: 11/30/2022] Open
Abstract
Advances in technology have ushered in a new era in the measurement and interpretation of surface-recorded electromyographic (EMG) signals. These developments have included improvements in detection systems, the algorithms used to decompose the interference signals, and the strategies used to edit the identified waveforms. To evaluate the validity of the results obtained with this new technology, the purpose of this review was to compare the results achieved by decomposing surface-recorded EMG signals into the discharge times of single motor units with what is known about the rate coding characteristics of single motor units based on recordings obtained with intramuscular electrodes. The characteristics compared were peak discharge rate, saturation of discharge rate during submaximal contractions, rate coding during fast contractions, the association between oscillations in force and discharge rate, and adjustments during fatiguing contractions. The comparison indicates that some decomposition methods are able to replicate many of the findings derived from intramuscular recordings, but additional improvements in the methods are required. Critically, more effort needs to be focused on editing the waveforms identified by the decomposition algorithms. With adequate attention to detail, this technology has the potential to augment our knowledge on motor unit physiology and to provide useful approaches that are being translated into clinical practice.
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Affiliation(s)
- Roger M Enoka
- Department of Integrative Physiology, University of Colorado, Boulder, CO, USA.
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Del Vecchio A, Casolo A, Negro F, Scorcelletti M, Bazzucchi I, Enoka R, Felici F, Farina D. The increase in muscle force after 4 weeks of strength training is mediated by adaptations in motor unit recruitment and rate coding. J Physiol 2019; 597:1873-1887. [PMID: 30727028 DOI: 10.1113/jp277250] [Citation(s) in RCA: 185] [Impact Index Per Article: 37.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2018] [Accepted: 12/03/2018] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Previous studies have indicated that several weeks of strength training is sufficient to elicit significant adaptations in the neural drive sent to the muscles. There are few data, however, on the changes elicited by strength training in the recruitment and rate coding of motor units during voluntary contractions. We show for the first time that the discharge characteristics of motor units in the tibialis anterior muscle tracked across the intervention are changed by 4 weeks of strength training with isometric voluntary contractions. The specific adaptations included significant increases in motor unit discharge rate, decreases in the recruitment-threshold force of motor units and a similar input-output gain of the motor neurons. The findings suggest that the adaptations in motor unit function may be attributable to changes in synaptic input to the motor neuron pool or to adaptations in intrinsic motor neuron properties. ABSTRACT The strength of a muscle typically begins to increase after only a few sessions of strength training. This increase is usually attributed to changes in the neural drive to muscle as a result of adaptations at the cortical or spinal level. We investigated the change in the discharge characteristics of large populations of longitudinally tracked motor units in tibialis anterior before and after 4 weeks of strength training the ankle-dorsiflexor muscles with isometric contractions. The adaptations exhibited by 14 individuals were compared with 14 control subjects. High-density electromyogram grids with 128 electrodes recorded the myoelectric activity during isometric ramp contractions to the target forces of 35%, 50% and 70% of maximal voluntary force. The motor unit recruitment and derecruitment thresholds, discharge rate, interspike intervals and estimates of synaptic inputs to motor neurons were assessed. The normalized recruitment-threshold forces of the motor units were decreased after strength training (P < 0.05). Moreover, discharge rate increased by 3.3 ± 2.5 pps (average across subjects and motor units) during the plateau phase of the submaximal isometric contractions (P < 0.001). Discharge rates at recruitment and derecruitment were not modified by training (P < 0.05). The association between force and motor unit discharge rate during the ramp-phase of the contractions was also not altered by training (P < 0.05). These results demonstrate for the first time that the increase in muscle force after 4 weeks of strength training is the result of an increase in motor neuron output from the spinal cord to the muscle.
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Affiliation(s)
- Alessandro Del Vecchio
- Department of Bioengineering, Imperial College London, London, UK.,Department of Movement, Human and Health Sciences, University of Rome 'Foro Italico', Rome, Italy
| | - Andrea Casolo
- Department of Bioengineering, Imperial College London, London, UK.,Department of Movement, Human and Health Sciences, University of Rome 'Foro Italico', Rome, Italy
| | - Francesco Negro
- Department of Clinical and Experimental Sciences, University of Brescia, Brescia, Italy
| | - Matteo Scorcelletti
- Department of Movement, Human and Health Sciences, University of Rome 'Foro Italico', Rome, Italy
| | - Ilenia Bazzucchi
- Department of Movement, Human and Health Sciences, University of Rome 'Foro Italico', Rome, Italy
| | - Roger Enoka
- Department of Integrative Physiology, University of Colorado Boulder, CO, USA
| | - Francesco Felici
- Department of Movement, Human and Health Sciences, University of Rome 'Foro Italico', Rome, Italy
| | - Dario Farina
- Department of Bioengineering, Imperial College London, London, UK
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MARTINEZ-VALDES EDUARDO, FARINA DARIO, NEGRO FRANCESCO, DEL VECCHIO ALESSANDRO, FALLA DEBORAH. Early Motor Unit Conduction Velocity Changes to High-Intensity Interval Training versus Continuous Training. Med Sci Sports Exerc 2018; 50:2339-2350. [DOI: 10.1249/mss.0000000000001705] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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19
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Effects of endurance training on neuromuscular fatigue in healthy active men. Part I: Strength loss and muscle fatigue. Eur J Appl Physiol 2018; 118:2281-2293. [PMID: 30121882 DOI: 10.1007/s00421-018-3950-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2018] [Accepted: 07/23/2018] [Indexed: 01/26/2023]
Abstract
PURPOSE The adaptations induced by endurance training on the neuromuscular function remain under investigation and, for methodological reasons, unclear. This study investigates the effects of cycling training on neuromuscular fatigue and its peripheral contribution measured during and immediately after cycling exercise. METHODS Fourteen healthy men performed a fatigue test before a 9-week cycling program (PRE) and two tests after training: at the same absolute power output as PRE (POSTABS) and based on the post-training maximal aerobic power (POSTREL). Throughout the tests and at exhaustion (EXH), maximal voluntary contraction (MVC) and peripheral fatigue were assessed in the quadriceps muscle by electrical nerve stimulation [single twitch (Pt); high-frequency doublet (Db100) and low-to-high-frequency ratio (Db10:100)]. RESULTS Time to EXH was longer in POSTABS than PRE (34 ± 5 vs. 27 ± 4 min, P < 0.001), and POSTREL tended to be longer than PRE (30 ± 6 min, P = 0.053). MVC and peripheral fatigue were overall less depressed in POSTABS than PRE at isotime. At EXH, MVC and Db10:100 were similarly reduced in all sessions (-37 to - 42% and - 30 to - 37%, respectively). Db100 tended to be less depressed in POSTABS than PRE (-40 ± 9 vs. - 48 ± 16%, P = 0.050) and in POSTREL than PRE (-39 ± 9%, P = 0.071). Pt decreased similarly in POSTABS and PRE (-52 ± 16 vs. - 54 ± 16%), but POSTREL tended to be less depressed than PRE (-48 ± 14%, P = 0.075). CONCLUSIONS This study confirms fatigue attenuation at isotime after training. Yet lower or similar fatigue at EXH indicates that, unlike previously suggested, fatigue tolerance may not be upregulated after 9 weeks of cycling training.
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Martinez-Valdes E, Negro F, Falla D, De Nunzio AM, Farina D. Surface electromyographic amplitude does not identify differences in neural drive to synergistic muscles. J Appl Physiol (1985) 2018; 124:1071-1079. [DOI: 10.1152/japplphysiol.01115.2017] [Citation(s) in RCA: 69] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Surface electromyographic (EMG) signal amplitude 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 amplitude was greater for VM than VL ( P < 0.001), whereas the EMG amplitude normalized with respect to MVC was greater for VL than VM ( P < 0.04). Because differences in EMG amplitude 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 amplitude between the two muscles (~63% of explained variance). These results indicate that EMG amplitude, even following normalization, does not reflect the neural drive to synergistic muscles. Moreover, absolute EMG amplitude is mainly explained by the size of MU action potentials. NEW & NOTEWORTHY Electromyographic (EMG) amplitude 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 amplitude and motor unit behavior. The results clarify the limitations of surface EMG to interpret differences in neural drive between muscles.
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Affiliation(s)
- Eduardo Martinez-Valdes
- Centre of Precision Rehabilitation for Spinal Pain, School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
- Department of Sports Medicine and Sports Orthopaedics, University of Potsdam, Potsdam, Germany
- Centro de Investigación en Fisiología del Ejercicio, Universidad Mayor, Santiago, Chile
| | - Francesco Negro
- Department of Clinical and Experimental Sciences, Università degli Studi di Brescia, Brescia, Italy
| | - Deborah Falla
- Centre of Precision Rehabilitation for Spinal Pain, School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Alessandro Marco De Nunzio
- Centre of Precision Rehabilitation for Spinal Pain, School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, United Kingdom
| | - Dario Farina
- Department of Bioengineering, Imperial College London, Royal School of Mines, London, United Kingdom
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Muddle TWD, Colquhoun RJ, Magrini MA, Luera MJ, DeFreitas JM, Jenkins NDM. Effects of fatiguing, submaximal high- versus low-torque isometric exercise on motor unit recruitment and firing behavior. Physiol Rep 2018; 6:e13675. [PMID: 29673119 PMCID: PMC5907942 DOI: 10.14814/phy2.13675] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2018] [Accepted: 03/02/2018] [Indexed: 12/04/2022] Open
Abstract
The purpose of this investigation was to evaluate the effects of repeated, high- (HT: 70% MVIC) versus low-torque (LT: 30% MVIC) isometric exercise performed to failure on motor unit (MU) recruitment and firing behavior of the vastus lateralis. Eighteen resistance-trained males (23.1 ± 3.8 years) completed familiarization, followed by separate experimental sessions in which they completed either HT or LT exercise to failure in random order. LT exercise resulted in a greater time to task failure and a more dramatic decline in the muscle's force capacity, but the total work completed was similar for HT and LT exercise. An examination of the firing trains from 4670 MUs recorded during exercise revealed that firing rates generally increased during HT and LT exercise, but were higher during HT than LT exercise. Furthermore, recruitment thresholds (RT) did not significantly change during HT exercise, whereas the RT of the smallest MUs increased and the RT for the moderate to large MUs decreased during LT exercise. Both HT and LT exercise resulted in the recruitment of additional higher threshold MUs in order to maintain torque production. However, throughout exercise, HT required the recruitment of larger MUs than did LT exercise. In a few cases, however, MUs were recruited by individuals during LT exercise that were similar in size and original (pre) RT to those detected during HT exercise. Thus, the ability to achieve full MU recruitment during LT exercise may be dependent on the subject. Consequently, our data emphasize the task and subject dependency of muscle fatigue.
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Affiliation(s)
- Tyler W. D. Muddle
- Applied Neuromuscular Physiology LaboratoryOklahoma State UniversityStillwaterOklahoma
| | - Ryan J. Colquhoun
- Applied Neuromuscular Physiology LaboratoryOklahoma State UniversityStillwaterOklahoma
| | - Mitchel A. Magrini
- Applied Neuromuscular Physiology LaboratoryOklahoma State UniversityStillwaterOklahoma
| | - Micheal J. Luera
- Applied Neuromuscular Physiology LaboratoryOklahoma State UniversityStillwaterOklahoma
| | - Jason M. DeFreitas
- Applied Neuromuscular Physiology LaboratoryOklahoma State UniversityStillwaterOklahoma
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Contessa P, Letizi J, De Luca G, Kline JC. Contribution from motor unit firing adaptations and muscle coactivation during fatigue. J Neurophysiol 2018. [PMID: 29537913 DOI: 10.1152/jn.00766.2017] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The control of motor unit firing behavior during fatigue is still debated in the literature. Most studies agree that the central nervous system increases the excitation to the motoneuron pool to compensate for decreased force contributions of individual motor units and sustain muscle force output during fatigue. However, some studies claim that motor units may decrease their firing rates despite increased excitation, contradicting the direct relationship between firing rates and excitation that governs the voluntary control of motor units. To investigate whether the control of motor units in fact changes with fatigue, we measured motor unit firing behavior during repeated contractions of the first dorsal interosseous (FDI) muscle while concurrently monitoring the activation of surrounding muscles, including the flexor carpi radialis, extensor carpi radialis, and pronator teres. Across all subjects, we observed an overall increase in FDI activation and motor unit firing rates by the end of the fatigue task. However, in some subjects we observed increases in FDI activation and motor unit firing rates only during the initial phase of the fatigue task, followed by subsequent decreases during the late phase of the fatigue task while the coactivation of surrounding muscles increased. These findings indicate that the strategy for sustaining force output may occasionally change, leading to increases in the relative activation of surrounding muscles while the excitation to the fatiguing muscle decreases. Importantly, irrespective of changes in the strategy for sustaining force output, the control properties regulating motor unit firing behavior remain unchanged during fatigue. NEW & NOTEWORTHY This work addresses sources of debate surrounding the manner in which motor unit firing behavior is controlled during fatigue. We found that decreases in the motor unit firing rates of the fatiguing muscle may occasionally be observed when the contribution of coactive muscles increases. Despite changes in the strategy employed to sustain the force output, the underlying control properties regulating motor unit firing behavior remain unchanged during muscle fatigue.
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Affiliation(s)
| | - John Letizi
- Delsys and Altec Inc. , Natick, Massachusetts
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Martinez-Valdes E, Falla D, Negro F, Mayer F, Farina D. Differential Motor Unit Changes after Endurance or High-Intensity Interval Training. Med Sci Sports Exerc 2017; 49:1126-1136. [PMID: 28121801 DOI: 10.1249/mss.0000000000001209] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
PURPOSE Using a novel technique of high-density surface EMG decomposition and motor unit (MU) tracking, we compared changes in the properties of vastus medialis and vastus lateralis MU after endurance (END) and high-intensity interval training (HIIT). METHODS Sixteen men were assigned to the END or the HIIT group (n = 8 each) and performed six training sessions for 14 d. Each session consisted of 8-12 × 60-s intervals at 100% peak power output separated by 75 s of recovery (HIIT) or 90-120 min continuous cycling at ~65% V˙O2peak (END). Pre- and postintervention, participants performed 1) incremental cycling to determine V˙O2peak and peak power output and 2) maximal, submaximal (10%, 30%, 50%, and 70% maximum voluntary contraction [MVC]), and sustained (until task failure at 30% MVC) isometric knee extensions while high-density surface EMG signals were recorded from the vastus medialis and vastus lateralis. EMG signals were decomposed (submaximal contractions) into individual MU by convolutive blind source separation. Finally, MU were tracked across sessions by semiblind source separation. RESULTS After training, END and HIIT improved V˙O2peak similarly (by 5.0% and 6.7%, respectively). The HIIT group showed enhanced maximal knee extension torque by ~7% (P = 0.02) and was accompanied by an increase in discharge rate for high-threshold MU (≥50% knee extension MVC) (P < 0.05). By contrast, the END group increased their time to task failure by ~17% but showed no change in MU discharge rates (P > 0.05). CONCLUSIONS HIIT and END induce different adjustments in MU discharge rate despite similar improvements in cardiopulmonary fitness. Moreover, the changes induced by HIIT are specific for high-threshold MU. For the first time, we show that HIIT and END induce specific neuromuscular adaptations, possibly related to differences in exercise load intensity and training volume.
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Affiliation(s)
- Eduardo Martinez-Valdes
- 1Department of Sports Medicine and Sports Orthopaedics, University of Potsdam, Potsdam, GERMANY; 2School of Sport, Exercise and Rehabilitation Sciences, Centre of Precision Rehabilitation for Spinal Pain (CPR Spine), College of Life and Environmental Sciences, University of Birmingham, Birmingham, UNITED KINGDOM; 3Department of Clinical and Experimental Sciences, Università degli Studi di Brescia, Brescia, ITALY; and 4Department of Bioengineering, Imperial College London, Royal School of Mines, London, UNITED KINGDOM
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Martinez-Valdes E, Negro F, Laine CM, Falla D, Mayer F, Farina D. Tracking motor units longitudinally across experimental sessions with high-density surface electromyography. J Physiol 2017; 595:1479-1496. [PMID: 28032343 PMCID: PMC5330923 DOI: 10.1113/jp273662] [Citation(s) in RCA: 106] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2016] [Accepted: 11/15/2016] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS Classic motor unit (MU) recording and analysis methods do not allow the same MUs to be tracked across different experimental sessions, and therefore, there is limited experimental evidence on the adjustments in MU properties following training or during the progression of neuromuscular disorders. We propose a new processing method to track the same MUs across experimental sessions (separated by weeks) by using high-density surface electromyography. The application of the proposed method in two experiments showed that individual MUs can be identified reliably in measurements separated by weeks and that changes in properties of the tracked MUs across experimental sessions can be identified with high sensitivity. These results indicate that the behaviour and properties of the same MUs can be monitored across multiple testing sessions. The proposed method opens new possibilities in the understanding of adjustments in motor unit properties due to training interventions or the progression of pathologies. ABSTRACT A new method is proposed for tracking individual motor units (MUs) across multiple experimental sessions on different days. The technique is based on a novel decomposition approach for high-density surface electromyography and was tested with two experimental studies for reliability and sensitivity. Experiment I (reliability): ten participants performed isometric knee extensions at 10, 30, 50 and 70% of their maximum voluntary contraction (MVC) force in three sessions, each separated by 1 week. Experiment II (sensitivity): seven participants performed 2 weeks of endurance training (cycling) and were tested pre-post intervention during isometric knee extensions at 10 and 30% MVC. The reliability (Experiment I) and sensitivity (Experiment II) of the measured MU properties were compared for the MUs tracked across sessions, with respect to all MUs identified in each session. In Experiment I, on average 38.3% and 40.1% of the identified MUs could be tracked across two sessions (1 and 2 weeks apart), for the vastus medialis and vastus lateralis, respectively. Moreover, the properties of the tracked MUs were more reliable across sessions than those of the full set of identified MUs (intra-class correlation coefficients ranged between 0.63-0.99 and 0.39-0.95, respectively). In Experiment II, ∼40% of the MUs could be tracked before and after the training intervention and training-induced changes in MU conduction velocity had an effect size of 2.1 (tracked MUs) and 1.5 (group of all identified motor units). These results show the possibility of monitoring MU properties longitudinally to document the effect of interventions or the progression of neuromuscular disorders.
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Affiliation(s)
- E Martinez-Valdes
- Department of Sports Medicine and Sports Orthopaedics, University of Potsdam, Potsdam, Germany
| | - F Negro
- Institute of Neurorehabilitation Systems, Bernstein Focus Neurotechnology Göttingen (BFNT), Bernstein Centre for Computational Neuroscience (BCCN), University Medical Center Göttingen, Georg-August University, Göttingen, Germany.,Department of Clinical and Experimental Sciences, Università degli Studi di Brescia, Brescia, Italy
| | - C M Laine
- Institute of Neurorehabilitation Systems, Bernstein Focus Neurotechnology Göttingen (BFNT), Bernstein Centre for Computational Neuroscience (BCCN), University Medical Center Göttingen, Georg-August University, Göttingen, Germany
| | - D Falla
- Centre of Precision Rehabilitation for Spinal Pain (CPR Spine), School of Sport, Exercise and Rehabilitation Sciences, College of Life and Environmental Sciences, University of Birmingham, Birmingham, UK
| | - F Mayer
- Department of Sports Medicine and Sports Orthopaedics, University of Potsdam, Potsdam, Germany
| | - D Farina
- Institute of Neurorehabilitation Systems, Bernstein Focus Neurotechnology Göttingen (BFNT), Bernstein Centre for Computational Neuroscience (BCCN), University Medical Center Göttingen, Georg-August University, Göttingen, Germany.,Department of Bioengineering, Imperial College London, Royal School of Mines, London, UK
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A new optical flow model for motor unit conduction velocity estimation in multichannel surface EMG. Comput Biol Med 2017; 83:59-68. [PMID: 28237905 DOI: 10.1016/j.compbiomed.2017.02.006] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2016] [Revised: 01/30/2017] [Accepted: 02/17/2017] [Indexed: 11/22/2022]
Abstract
Many studies have demonstrated the feasibility and benefits of Conduction Velocity (CV) estimation from surface electromyograms (EMGs) in various experimental conditions. Among them, a method based on optical flow was proposed recently, demonstrating relatively accurate CV estimation for EMG signals acquired in monopolar mode. We extended this method by a new data model that compensates more realistically for the spatial Motor Unit Action Potential (MUAP) shape variability and enables accurate CV estimation also in single-differential acquisition mode. The proposed modification was validated on 5000 synthetic Motor Units (MUs) with known CV and direction of fibres. It was shown that, in the noiseless case, the mean CV estimation error was significantly lower for our proposed modification compared to the original CV estimation procedure by up to 2% in the case of monopolar EMG signals and by up to 18.6% for single-differential EMG signals. When estimating fibre directions, the mean error was lower by up to 2.4° (for monopolar EMG signals) and 9.6° (for single-differential EMG signals). The results of tests with 10dB and 20dB noise further demonstrated the robustness of the proposed algorithm to noise in MUAP estimation.
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Röhrle O, Neumann V, Heidlauf T. The Role of Parvalbumin, Sarcoplasmatic Reticulum Calcium Pump Rate, Rates of Cross-Bridge Dynamics, and Ryanodine Receptor Calcium Current on Peripheral Muscle Fatigue: A Simulation Study. COMPUTATIONAL AND MATHEMATICAL METHODS IN MEDICINE 2016; 2016:3180205. [PMID: 27980606 PMCID: PMC5131563 DOI: 10.1155/2016/3180205] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/15/2016] [Revised: 07/18/2016] [Accepted: 08/21/2016] [Indexed: 11/23/2022]
Abstract
A biophysical model of the excitation-contraction pathway, which has previously been validated for slow-twitch and fast-twitch skeletal muscles, is employed to investigate key biophysical processes leading to peripheral muscle fatigue. Special emphasis hereby is on investigating how the model's original parameter sets can be interpolated such that realistic behaviour with respect to contraction time and fatigue progression can be obtained for a continuous distribution of the model's parameters across the muscle units, as found for the functional properties of muscles. The parameters are divided into 5 groups describing (i) the sarcoplasmatic reticulum calcium pump rate, (ii) the cross-bridge dynamics rates, (iii) the ryanodine receptor calcium current, (iv) the rates of binding of magnesium and calcium ions to parvalbumin and corresponding dissociations, and (v) the remaining processes. The simulations reveal that the first two parameter groups are sensitive to contraction time but not fatigue, the third parameter group affects both considered properties, and the fourth parameter group is only sensitive to fatigue progression. Hence, within the scope of the underlying model, further experimental studies should investigate parvalbumin dynamics and the ryanodine receptor calcium current to enhance the understanding of peripheral muscle fatigue.
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Affiliation(s)
- Oliver Röhrle
- Institute of Applied Mechanics (CE), University of Stuttgart, Stuttgart, Germany
- Stuttgart Research Centre for Simulation Technology (SimTech), University of Stuttgart, Stuttgart, Germany
| | - Verena Neumann
- Institute of Applied Mechanics (CE), University of Stuttgart, Stuttgart, Germany
| | - Thomas Heidlauf
- Institute of Applied Mechanics (CE), University of Stuttgart, Stuttgart, Germany
- Stuttgart Research Centre for Simulation Technology (SimTech), University of Stuttgart, Stuttgart, Germany
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Contessa P, De Luca CJ, Kline JC. The compensatory interaction between motor unit firing behavior and muscle force during fatigue. J Neurophysiol 2016; 116:1579-1585. [PMID: 27385798 DOI: 10.1152/jn.00347.2016] [Citation(s) in RCA: 71] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2016] [Accepted: 07/05/2016] [Indexed: 11/22/2022] Open
Abstract
Throughout the literature, different observations of motor unit firing behavior during muscle fatigue have been reported and explained with varieties of conjectures. The disagreement amongst previous studies has resulted, in part, from the limited number of available motor units and from the misleading practice of grouping motor unit data across different subjects, contractions, and force levels. To establish a more clear understanding of motor unit control during fatigue, we investigated the firing behavior of motor units from the vastus lateralis muscle of individual subjects during a fatigue protocol of repeated voluntary constant force isometric contractions. Surface electromyographic decomposition technology provided the firings of 1,890 motor unit firing trains. These data revealed that to sustain the contraction force as the muscle fatigued, the following occurred: 1) motor unit firing rates increased; 2) new motor units were recruited; and 3) motor unit recruitment thresholds decreased. Although the degree of these adaptations was subject specific, the behavior was consistent in all subjects. When we compared our empirical observations with those obtained from simulation, we found that the fatigue-induced changes in motor unit firing behavior can be explained by increasing excitation to the motoneuron pool that compensates for the fatigue-induced decrease in muscle force twitch reported in empirical studies. Yet, the fundamental motor unit control scheme remains invariant throughout the development of fatigue. These findings indicate that the central nervous system regulates motor unit firing behavior by adjusting the operating point of the excitation to the motoneuron pool to sustain the contraction force as the muscle fatigues.
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Affiliation(s)
| | - Carlo J De Luca
- Delsys Incorporated, Natick, Massachusetts; and Department of Biomedical Engineering, Boston University, Boston, Massachusetts
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Kerasnoudis A. Ultrasound visualization of nerve remodeling after strenuous exercise. Muscle Nerve 2015; 53:320-4. [PMID: 26492568 DOI: 10.1002/mus.24948] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/20/2015] [Indexed: 11/12/2022]
Abstract
INTRODUCTION The aim of this case study is to describe the use of nerve ultrasound to visualize the morphological changes that occur during conduction velocity alterations after strenuous exercise. METHODS A 32-year-old, healthy runner underwent clinical, electrophysiological, and ultrasound evaluation 24 hours before, 30 minutes after, and 24 hours after a marathon. RESULTS An increase in motor conduction velocity of the median, ulnar, radial, and tibial nerves and sensory conduction velocity of the median and ulnar nerves was found between pre- and post-marathon studies. An increase in the cross-sectional area of the median (carpal tunnel), ulnar (Guyon canal and elbow), fibular (fibular head), and tibial (ankle) nerves was documented. No changes in the MRC sum scale score of the various peripheral nerves were detected. CONCLUSION The case described shows the morphological changes that occur in healthy peripheral nerves during conduction velocity alterations.
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Physiological and Neural Adaptations to Eccentric Exercise: Mechanisms and Considerations for Training. BIOMED RESEARCH INTERNATIONAL 2015; 2015:193741. [PMID: 26543850 PMCID: PMC4620252 DOI: 10.1155/2015/193741] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Received: 11/17/2014] [Revised: 01/13/2015] [Accepted: 02/09/2015] [Indexed: 11/08/2022]
Abstract
Eccentric exercise is characterized by initial unfavorable effects such as subcellular muscle damage, pain, reduced fiber excitability, and initial muscle weakness. However, stretch combined with overload, as in eccentric contractions, is an effective stimulus for inducing physiological and neural adaptations to training. Eccentric exercise-induced adaptations include muscle hypertrophy, increased cortical activity, and changes in motor unit behavior, all of which contribute to improved muscle function. In this brief review, neuromuscular adaptations to different forms of exercise are reviewed, the positive training effects of eccentric exercise are presented, and the implications for training are considered.
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Mettler JA, Griffin L. Muscular endurance training and motor unit firing patterns during fatigue. Exp Brain Res 2015; 234:267-76. [DOI: 10.1007/s00221-015-4455-x] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2015] [Accepted: 09/23/2015] [Indexed: 12/01/2022]
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Behrens M, Weippert M, Wassermann F, Bader R, Bruhn S, Mau-Moeller A. Neuromuscular function and fatigue resistance of the plantar flexors following short-term cycling endurance training. Front Physiol 2015; 6:145. [PMID: 26029114 PMCID: PMC4429572 DOI: 10.3389/fphys.2015.00145] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2015] [Accepted: 04/21/2015] [Indexed: 12/02/2022] Open
Abstract
Previously published studies on the effect of short-term endurance training on neuromuscular function of the plantar flexors have shown that the H-reflex elicited at rest and during weak voluntary contractions was increased following the training regime. However, these studies did not test H-reflex modulation during isometric maximum voluntary contraction (iMVC) and did not incorporate a control group in their study design to compare the results of the endurance training group to individuals without the endurance training stimulus. Therefore, this randomized controlled study was directed to investigate the neuromuscular function of the plantar flexors at rest and during iMVC before and after 8 weeks of cycling endurance training. Twenty-two young adults were randomly assigned to an intervention group and a control group. During neuromuscular testing, rate of torque development, isometric maximum voluntary torque and muscle activation were measured. Triceps surae muscle activation and tibialis anterior muscle co-activation were assessed by normalized root mean square of the EMG signal during the initial phase of contraction (0–100, 100–200 ms) and iMVC of the plantar flexors. Furthermore, evoked spinal reflex responses of the soleus muscle (H-reflex evoked at rest and during iMVC, V-wave), peak twitch torques induced by electrical stimulation of the posterior tibial nerve at rest and fatigue resistance were evaluated. The results indicate that cycling endurance training did not lead to a significant change in any variable of interest. Data of the present study conflict with the outcome of previously published studies that have found an increase in H-reflex excitability after endurance training. However, these studies had not included a control group in their study design as was the case here. It is concluded that short-term cycling endurance training does not necessarily enhance H-reflex responses and fatigue resistance.
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Affiliation(s)
- Martin Behrens
- Institute of Sport Science, University of Rostock Rostock, Germany
| | - Matthias Weippert
- Institute of Sport Science, University of Rostock Rostock, Germany ; Institute of Exercise Physiology and Public Health Rostock, Germany
| | | | - Rainer Bader
- Department of Orthopaedics, University Medicine Rostock Rostock, Germany
| | - Sven Bruhn
- Institute of Sport Science, University of Rostock Rostock, Germany
| | - Anett Mau-Moeller
- Department of Orthopaedics, University Medicine Rostock Rostock, Germany
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Herda TJ, Zuniga JM, Ryan ED, Camic CL, Bergstrom HC, Smith DB, Weir JP, Cramer JT, Housh TJ. The influence of electromyographic recording methods and the innervation zone on the mean power frequency-torque relationships. J Electromyogr Kinesiol 2015; 25:423-30. [PMID: 25851079 DOI: 10.1016/j.jelekin.2015.02.013] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2014] [Revised: 01/30/2015] [Accepted: 02/27/2015] [Indexed: 10/23/2022] Open
Abstract
This study examined the effects of electromyographic (EMG) recording methods and innervation zone (IZ) on the mean power frequency (MPF)-torque relationships. Nine subjects performed isometric ramp muscle actions of the leg extensors from 5% to 100% of maximal voluntary contraction with an eight channel linear electrode array over the IZ of the vastus lateralis. The slopes were calculated from the log-transformed monopolar and bipolar EMG MPF-torque relationships for each channel and subject and 95% confidence intervals (CI) were constructed around the slopes for each relationship and the composite of the slopes. Twenty-two to 55% of the subjects exhibited 95% CIs that did not include a slope of zero for the monopolar EMG MPF-torque relationships while 25-75% of the subjects exhibited 95% CIs that did not include a slope of zero for the bipolar EMG MPF-torque relationships. The composite of the slopes from the EMG MPF-torque relationships were not significantly different from zero for any method or channel, however, the method and IZ location slightly influenced the number of significant slopes on a subject-by-subject basis. The log-transform model indicated that EMG MPF-torque patterns were nonlinear regardless of recording method or distance from the IZ.
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Affiliation(s)
- Trent J Herda
- Department of Health, Sport, and Exercise Sciences, Neuromechanics Laboratory, University of Kansas, Lawrence, KS, USA.
| | - Jorge M Zuniga
- Exercise Science Department, Creighton University, Omaha, NE, USA
| | - Eric D Ryan
- Department of Exercise and Sport Science, Neuromuscular Research Laboratory, University of North Carolina - Chapel Hill, Chapel Hill, NC, USA
| | - Clayton L Camic
- Exercise and Sport Science Department, University of Wisconsin-La Crosse, La Crosse, WI, USA
| | - Haley C Bergstrom
- Department of Kinesiology and Health Promotion, University of Kentucky, Lexington, KY, USA
| | - Doug B Smith
- Department of Health and Human Performance, Oklahoma State University, Stillwater, OK, USA
| | - Joseph P Weir
- Department of Health, Sport, and Exercise Sciences, Neuromechanics Laboratory, University of Kansas, Lawrence, KS, USA
| | - Joel T Cramer
- Department of Nutrition and Health Sciences, University of Nebraska-Lincoln, Lincoln, NE, USA
| | - Terry J Housh
- Department of Nutrition and Health Sciences, University of Nebraska-Lincoln, Lincoln, NE, USA
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Zghal F, Cottin F, Kenoun I, Rebaï H, Moalla W, Dogui M, Tabka Z, Martin V. Improved tolerance of peripheral fatigue by the central nervous system after endurance training. Eur J Appl Physiol 2015; 115:1401-15. [PMID: 25681110 DOI: 10.1007/s00421-015-3123-y] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2014] [Accepted: 02/03/2015] [Indexed: 11/28/2022]
Abstract
PURPOSE The purposes of this study were to evaluate the effect of endurance training on central fatigue development and recovery. METHODS A control group was compared to a training group, which followed an 8-week endurance-training program, consisting in low-force concentric and isometric contractions. Before (PRE) and after (POST) the training period, neuromuscular function of the knee extensor (KE) muscles was evaluated before, immediately after and during 33 min after an exhausting submaximal isometric task at 15 % of the maximal voluntary contraction (MVC) force. After training, the trained group performed another test at iso-time, i.e., with the task maintained until the duration completed before training was matched (POST2). The evaluation of neuromuscular function consisted in the determination of the voluntary activation level during MVCs, from peripheral nerve electrical (VAPNS) and transcranial magnetic stimulations (VATMS). The amplitude of the potentiated twitch (Pt), the evoked [motor evoked potentials, cortical silent period (CSP)] and voluntary EMG activities were also recorded on the KE muscles. RESULTS Before training, the isometric task induced significant reductions of VAPNS, VATMS and Pt, and an increased CSP. The training period induced a threefold increase of exercise duration, delayed central fatigue appearance, as illustrated by the absence of modification of VAPNS, VATMS and CSP after POST2. At POST, central fatigue magnitude and recovery were not modified but Pt reduction was greater. CONCLUSION These results suggest that central fatigue partially adapts to endurance training. This adaptation principally translates into improved tolerance of peripheral fatigue by the central nervous system.
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Affiliation(s)
- F Zghal
- UBIAE (INSERM U902), Faculty of Sport Sciences, Val d'Essonne University, Evry, France
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Application of the Framework for Exercise Prescription. TOPICS IN GERIATRIC REHABILITATION 2014. [DOI: 10.1097/tgr.0000000000000012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Lin YT, Kuo CH, Hwang IS. Fatigue effect on low-frequency force fluctuations and muscular oscillations during rhythmic isometric contraction. PLoS One 2014; 9:e85578. [PMID: 24465605 PMCID: PMC3897466 DOI: 10.1371/journal.pone.0085578] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2013] [Accepted: 11/28/2013] [Indexed: 11/19/2022] Open
Abstract
Continuous force output containing numerous intermittent force pulses is not completely smooth. By characterizing force fluctuation properties and force pulse metrics, this study investigated adaptive changes in trajectory control, both force-generating capacity and force fluctuations, as fatigue progresses. Sixteen healthy subjects (20-24 years old) completed rhythmic isometric gripping with the non-dominant hand to volitional failure. Before and immediately following the fatigue intervention, we measured the gripping force to couple a 0.5 Hz sinusoidal target in the range of 50-100% maximal voluntary contraction. Dynamic force output was off-line decomposed into 1) an ideal force trajectory spectrally identical to the target rate; and 2) a force pulse trace pertaining to force fluctuations and error-correction attempts. The amplitude of ideal force trajectory regarding to force-generating capacity was more suppressed than that of the force pulse trace with increasing fatigue, which also shifted the force pulse trace to lower frequency bands. Multi-scale entropy analysis revealed that the complexity of the force pulse trace at high time scales increased with fatigue, contrary to the decrease in complexity of the force pulse trace at low time scales. Statistical properties of individual force pulses in the spatial and temporal domains varied with muscular fatigue, concurrent with marked suppression of gamma muscular oscillations (40-60 Hz) in the post-fatigue test. In conclusion, this study first reveals that muscular fatigue impairs the amplitude modulation of force pattern generation more than it affects the amplitude responsiveness of fine-tuning a force trajectory. Besides, motor fatigue results disadvantageously in enhancement of motor noises, simplification of short-term force-tuning strategy, and slow responsiveness to force errors, pertaining to dimensional changes in force fluctuations, scaling properties of force pulse, and muscular oscillation.
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Affiliation(s)
- Yen-Ting Lin
- Physical Education Office, Asia University, Taichung, Taiwan
- Department of Sports Sciences, University of Taipei, Taipei, Taiwan
| | - Chia-Hua Kuo
- Department of Sports Sciences, University of Taipei, Taipei, Taiwan
| | - Ing-Shiou Hwang
- Department of Physical Therapy, College of Medicine, National Cheng Kung University, Tainan, Taiwan
- Institute of Allied Health Sciences, National Cheng Kung University, Tainan, Taiwan
- * E-mail:
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Zghal F, Martin V, Thorkani A, Arnal PJ, Tabka Z, Cottin F. Effects of endurance training on the maximal voluntary activation level of the knee extensor muscles. Eur J Appl Physiol 2013; 114:683-93. [PMID: 24368553 DOI: 10.1007/s00421-013-2793-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2013] [Accepted: 12/06/2013] [Indexed: 10/25/2022]
Abstract
PURPOSE The aim of this study was to investigate the neural adaptations to endurance training, and more specifically the adaptation of the cortical voluntary activation of the knee extensor (KE) muscles. METHODS Sixteen sedentary men were randomly allocated into an endurance training (n = 8) or a control group (n = 8). All subjects performed a maximal aerobic speed test (MAS) before and immediately after the training period. Training lasted 8 weeks and was based on endurance running. During Pre- and Post-training testing sessions, maximal voluntary contraction (MVC) was measured and voluntary activation (VA) was calculated via peripheral nerve (PNS) and transcranial magnetic stimulations (TMS) superimposed to MVC. Electromyographic activity (EMG) of the KE muscles was also measured during MVC, PNS (M-wave) and TMS (motor evoked potentials-MEP). The cortical silent period following TMS was also assessed. RESULTS Despite a significant improvement in endurance running performance, as suggested by the increase of MAS in the training group (Pre 15.4 ± 1.6 vs. Post 16.4 ± 1.6 km·h(-1)), endurance training did not affect MVC or VA as measured with PNS and TMS. Similarly, the EMG of KE muscles during MVC did not show any significant changes. Furthermore, the MEP amplitude and the duration of the silent period also remained unchanged after endurance training. CONCLUSIONS The present study suggests an 8-week endurance-training program does not generate adaptations of neural factors in sedentary subjects.
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Affiliation(s)
- F Zghal
- UBIAE (INSERM U902), Faculty of Sport Sciences, Val d'Essonne University, Evry, France
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