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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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Beausejour JP, Bohlen P, Harmon KK, Girts RM, Pagan JI, Hahs-Vaughn DL, Herda TJ, Stock MS. A comparison of techniques for verifying the accuracy of precision decomposition-derived relationships between motor unit firing rates and recruitment thresholds from surface EMG signals. Exp Brain Res 2023; 241:2547-2560. [PMID: 37707570 DOI: 10.1007/s00221-023-06694-7] [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: 03/15/2023] [Accepted: 08/21/2023] [Indexed: 09/15/2023]
Abstract
Approaches for validating motor unit firing times following surface electromyographic (EMG) signal decomposition with the precision decomposition III (PDIII) algorithm have not been agreed upon. Two approaches have been common: (1) "reconstruct-and-test" and (2) spike-triggered averaging (STA). We sought to compare motor unit results following the application of these approaches. Surface EMG signals were recorded from the vastus lateralis of 13 young males performing trapezoidal, isometric knee extensions at 50% and 80% of maximum voluntary contraction (MVC) force. The PDIII algorithm was used to quantify motor unit firing rates. Motor units were excluded using eight combinations of the reconstruct-and-test approach with accuracy thresholds of 0, 90, 91, and 92% with and without STA. The mean firing rate versus recruitment threshold relationship was minimally affected by STA. At 80% MVC, slopes acquired at the 0% accuracy threshold were significantly greater (i.e., less negative) than when 91% (p = .010) and 92% (p = .030) accuracy thresholds were applied. The application of STA has minimal influence on surface EMG signal decomposition results. Stringent reconstruct-and-test accuracy thresholds influence motor unit-derived relationships at high forces, perhaps explained through the increased presence of large motor unit action potentials. Investigators using the PDIII algorithm can expect negligible changes in motor unit-derived linear regression relationships with the application of secondary validation procedures.
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Affiliation(s)
- Jonathan P Beausejour
- Neuromuscular Plasticity Laboratory, Institute of Exercise Physiology and Rehabilitation Science, University of Central Florida, 4000 Central Florida Blvd, Orlando, FL, 32816-2205, USA
- School of Kinesiology and Rehabilitation Sciences, University of Central Florida, Orlando, FL, USA
| | - Paul Bohlen
- Neuromuscular Plasticity Laboratory, Institute of Exercise Physiology and Rehabilitation Science, University of Central Florida, 4000 Central Florida Blvd, Orlando, FL, 32816-2205, USA
- School of Kinesiology and Rehabilitation Sciences, University of Central Florida, Orlando, FL, USA
| | - Kylie K Harmon
- Department of Exercise Science, Syracuse University, Syracuse, NY, USA
| | - Ryan M Girts
- Department of Natural and Health Sciences, Pfeiffer University, Misenheimer, NC, USA
| | - Jason I Pagan
- Neuromuscular Plasticity Laboratory, Institute of Exercise Physiology and Rehabilitation Science, University of Central Florida, 4000 Central Florida Blvd, Orlando, FL, 32816-2205, USA
- School of Kinesiology and Rehabilitation Sciences, University of Central Florida, Orlando, FL, USA
| | - Debbie L Hahs-Vaughn
- College of Community Innovation and Education, University of Central Florida, Orlando, FL, USA
| | - Trent J Herda
- Neuromechanics Laboratory, Department of Health, Sport and Exercise Sciences, University of Kansas, Lawrence, USA
| | - Matt S Stock
- Neuromuscular Plasticity Laboratory, Institute of Exercise Physiology and Rehabilitation Science, University of Central Florida, 4000 Central Florida Blvd, Orlando, FL, 32816-2205, USA.
- School of Kinesiology and Rehabilitation Sciences, University of Central Florida, Orlando, FL, USA.
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Olmos AA, Sterczala AJ, Parra ME, Dimmick HL, Miller JD, Deckert JA, Sontag SA, Gallagher PM, Fry AC, Herda TJ, Trevino MA. Sex-related differences in motor unit behavior are influenced by myosin heavy chain during high- but not moderate-intensity contractions. Acta Physiol (Oxf) 2023; 239:e14024. [PMID: 37551144 DOI: 10.1111/apha.14024] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2022] [Revised: 07/18/2023] [Accepted: 07/19/2023] [Indexed: 08/09/2023]
Abstract
AIMS Motor unit recruitment and firing rate patterns of the vastus lateralis (VL) have not been compared between sexes during moderate- and high-intensity contraction intensities. Additionally, the influence of fiber composition on potential sex-related differences remains unquantified. METHODS Eleven males and 11 females performed 40% and 70% maximal voluntary contractions (MVCs). Surface electromyographic (EMG) signals recorded from the VL were decomposed. Recruitment thresholds (RTs), MU action potential amplitudes (MUAPAMP ), initial firing rates (IFRs), mean firing rates (MFRs), and normalized EMG amplitude (N-EMGRMS ) at steady torque were analyzed. Y-intercepts and slopes were calculated for MUAPAMP , IFR, and MFR versus RT relationships. Type I myosin heavy chain isoform (MHC) was determined with muscle biopsies. RESULTS There were no sex-related differences in MU characteristics at 40% MVC. At 70% MVC, males exhibited greater slopes (p = 0.002) for the MUAPAMP , whereas females displayed greater slopes (p = 0.001-0.007) for the IFR and MFR versus RT relationships. N-EMGRMS at 70% MVC was greater for females (p < 0.001). Type I %MHC was greater for females (p = 0.006), and was correlated (p = 0.018-0.031) with the slopes for the MUAPAMP , IFR, and MFR versus RT relationships at 70% MVC (r = -0.599-0.585). CONCLUSION Both sexes exhibited an inverse relationship between MU firing rates and recruitment thresholds. However, the sex-related differences in MU recruitment and firing rate patterns and N-EMGRMS at 70% MVC were likely due to greater type I% MHC and smaller twitch forces of the higher threshold MUs for the females. Evidence is provided that muscle fiber composition may explain divergent MU behavior between sexes.
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Affiliation(s)
- Alex A Olmos
- Applied Neuromuscular Physiology Lab, Department of Kinesiology, Applied Health, and Recreation, Oklahoma State University, Stillwater, Oklahoma, USA
| | - Adam J Sterczala
- Neuromuscular Research Laboratory, Department of Sports Medicine and Nutrition, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Mandy E Parra
- School of Exercise and Sport Science, University of Mary Hardin-Baylor, Belton, Texas, USA
| | - Hannah L Dimmick
- Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada
| | - Jonathan D Miller
- Department of Chemical and Petroleum Engineering, University of Kansas, Lawrence, Kansas, USA
| | - Jake A Deckert
- Department of Human Physiology, Gonzaga University, Spokane, Washington, USA
| | - Stephanie A Sontag
- Applied Neuromuscular Physiology Lab, Department of Kinesiology, Applied Health, and Recreation, Oklahoma State University, Stillwater, Oklahoma, USA
| | - Philip M Gallagher
- Applied Physiology Laboratory, Department of Health, Sport, and Exercise Sciences, University of Kansas, Lawrence, Kansas, USA
| | - Andrew C Fry
- Jayhawk Athletic Performance Laboratory - Wu Tsai Human Performance Alliance, University of Kansas, Lawrence, Kansas, USA
| | - Trent J Herda
- Neuromechanics Laboratory, Department of Health, Sport, and Exercise Sciences, University of Kansas, Lawrence, Kansas, USA
| | - Michael A Trevino
- Applied Neuromuscular Physiology Lab, Department of Kinesiology, Applied Health, and Recreation, Oklahoma State University, Stillwater, Oklahoma, USA
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Trevino M, Perez S, Sontag S, Olmos A, Jeon S, Richardson L. Influence of Pennation Angle and Muscle Thickness on Mechanomyographic Amplitude-Torque Relationships and Sex-Related Differences in the Vastus Lateralis. J Funct Morphol Kinesiol 2023; 8:jfmk8020053. [PMID: 37218849 DOI: 10.3390/jfmk8020053] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/25/2023] [Revised: 04/17/2023] [Accepted: 04/27/2023] [Indexed: 05/24/2023] Open
Abstract
This study examined potential sex-related differences and correlations among the pennation angle (PA), muscle thickness (MT), and mechanomyographic amplitude (MMGRMS)-torque relationships of the vastus lateralis (VL) in 11 healthy males and 12 healthy females. The PA and MT of the VL were quantified with ultrasound. Participants performed an isometric muscle action of the knee extensors that linearly increased to 70% of maximal strength followed by a 12 s plateau. MMG was recorded from the VL. Linear regression models were fit to the log-transformed MMGRMS-torque relationships to calculate b terms (slopes) for the linearly increasing segment. MMGRMS was averaged during the plateau. Males exhibited greater PA (p < 0.001), MT (p = 0.027), b terms (p = 0.005), and MMGRMS (p = 0.016). The b terms were strongly (p < 0.001, r = 0.772) and moderately correlated (p = 0.004, r = 0.571) with PA and MT, respectively, while MMGRMS was moderately correlated with PA (p = 0.018, r = 0.500) and MT (p = 0.014, r = 0.515). The greater mechanical behavior of individuals possessing a larger PA and MT of the VL may reflect increased cross-bridge activity within the muscle fibers. Additionally, PA may help explain sex-related differences in MMGRMS between sexes.
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Affiliation(s)
- Michael Trevino
- Applied Neuromuscular Physiology Laboratory, Department of Kinesiology, Applied Health, and Recreation, Oklahoma State University, Stillwater, OK 74078, USA
| | - Sergio Perez
- Applied Neuromuscular Physiology Laboratory, Department of Kinesiology, Applied Health, and Recreation, Oklahoma State University, Stillwater, OK 74078, USA
| | - Stephanie Sontag
- Applied Neuromuscular Physiology Laboratory, Department of Kinesiology, Applied Health, and Recreation, Oklahoma State University, Stillwater, OK 74078, USA
| | - Alex Olmos
- Applied Neuromuscular Physiology Laboratory, Department of Kinesiology, Applied Health, and Recreation, Oklahoma State University, Stillwater, OK 74078, USA
| | - Sunggun Jeon
- Applied Neuromuscular Physiology Laboratory, Department of Kinesiology, Applied Health, and Recreation, Oklahoma State University, Stillwater, OK 74078, USA
| | - Lyric Richardson
- Applied Neuromuscular Physiology Laboratory, Department of Kinesiology, Applied Health, and Recreation, Oklahoma State University, Stillwater, OK 74078, USA
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A noninvasive test for estimating myosin heavy chain of the vastus lateralis in females with mechanomyography. Med Eng Phys 2023; 111:103946. [PMID: 36792240 DOI: 10.1016/j.medengphy.2022.103946] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2022] [Revised: 11/30/2022] [Accepted: 12/19/2022] [Indexed: 12/24/2022]
Abstract
This study examined relationships between percent myosin heavy chain (%MHC) expression and mechanomyographic amplitude (MMGRMS). Fifteen females (age ± SD=21.3 ± 5.3 yrs) completed isometric trapezoidal contractions at 30% and 70% maximal voluntary contraction (MVC). MMG was recorded from the vastus lateralis (VL). Participants gave a muscle biopsy of the VL post-testing. MMGRMS-torque relationships during the linearly varying segments were log-transformed and linear regressions were applied to calculate b terms (slopes). For the steady torque segment, MMGRMS was averaged. Correlations were performed for type I%MHC with the MMG variables. Multiple regression was utilized to examine prediction equations for type I%MHC. Type I%MHC was significantly correlated with the b terms during the increasing segment of the 70% MVC (p = 0.003; r = -0.718), and MMGRMS during steady torque at 30% (p = 0.008; r = -0.652) and 70% MVC (p = 0.040; r = -0.535). Type I%MHC reduced the linearity of the MMGRMS-torque relationship during the high-intensity linearly increasing segment, and MMGRMS at a low- and high-intensity steady torque. A combination of MMG variables estimated type I%MHC expression with 81.2% accuracy. MMG recorded during a low- and high-intensity isometric trapezoidal contraction may offer a simple, noninvasive test for estimating type I%MHC expression of the VL in sedentary females.
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Effects of Endurance Cycling on Mechanomyographic Median Power Frequency of the Vastus Lateralis. APPLIED SCIENCES-BASEL 2022. [DOI: 10.3390/app12105213] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
This study examined the effects of cycling training on mechanomyographic median power frequency (MMGMDF)–torque relationships of the vastus lateralis (VL). Ten males (Age ± SD; 20.20 ± 1.87 years) and 14 females (21.93 ± 5.33 years) performed isometric trapezoidal muscle actions with the knee extensors at 40% maximal voluntary contraction (MVC) before (PRE) and following 10 weeks of cycling training at the same absolute submaximal torque as pre-training (POSTABS). MMGMDF–torque relationships (increasing and decreasing segment) were log-transformed and b terms (slopes) were calculated. MMGMDF was averaged during steady torque. For POSTABS, the b terms for the females (0.133 ± 0.190) were greater than for the males (−0.083 ± 0.200; p = 0.013) and compared to PRE (0.008 ± 0.161; p = 0.036). At PRE, the b terms for the linearly increasing-muscle action (0.123 ± 0.192) were greater compared to the linearly decreasing-muscle action (−0.061 ± 0.188; p < 0.001), whereas no differences existed between muscle actions for POSTABS (p > 0.05). In conclusion, 10 weeks of cycling training resulted in different motor unit (MU) control strategies between sexes and altered MU control strategies between muscle actions for the VL during a moderate-intensity contraction.
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Jenkins ND, Miramonti AA, Hill EC, Smith CM, Cochrane-Snyman KC, Housh TJ, Cramer JT. Mechanomyographic Amplitude Is Sensitive to Load-Dependent Neuromuscular Adaptations in Response to Resistance Training. J Strength Cond Res 2021; 35:3265-3269. [DOI: 10.1519/jsc.0000000000003276] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Abstract
Although several methods have been used to estimate exercise-induced changes in human neuronal networks, there are growing doubts about the methodologies used. This review describes a single motor unit-based method that minimizes the errors inherent in classical methods. With this method, it is now possible to identify human neuronal networks' changes due to exercise.
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Affiliation(s)
- Kemal S Türker
- Istanbul Gelisim University, Faculty of Dentistry, Istanbul, Turkey
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9
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Endurance training alters motor unit activation strategies for the vastus lateralis, yet sex-related differences and relationships with muscle size remain. Eur J Appl Physiol 2021; 121:1367-1377. [PMID: 33604695 DOI: 10.1007/s00421-021-04622-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2020] [Accepted: 02/05/2021] [Indexed: 10/22/2022]
Abstract
PURPOSE To examine the effects of 10 weeks of endurance cycling training on mechanomyographic amplitude (MMGRMS)-torque relationships and muscle cross-sectional area (mCSA) of the vastus lateralis (VL) for 10 sedentary males (Age ± SD; 20.2 ± 1.9 years) and 14 sedentary females (21.9 ± 5.3 years). METHODS Participants performed maximal voluntary contractions (MVCs) and an isometric ramp up muscle action to 70% MVC of the knee extensors before (PRE) and after training at the same absolute pre-treatment submaximal torque (POSTABS). MMG was recorded from the VL and b terms were calculated from the natural log-transformed MMGRMS-torque relationships for each subject. mCSA was determined with ultrasonography. RESULTS Cycling decreased MVCs from pre- (168.10 ± 58.49 Nm) to post-training (160.78 ± 58.39 Nm; p = 0.005) without changes in mCSA. The b terms were greater for POSTABS (0.623 ± 0.204) than PRE (0.540 ± 0.226; p = 0.012) and for males (0.717 ± 0.171) than females (0.484 ± 0.168; p = 0.003). mCSA was correlated with the b terms for PRE (p < 0.001, r = 0.674) and POSTABS (p = 0.020, r = 0.471). CONCLUSION The decrease in MVC and increase in MMGRMS (b terms) post-training suggests increased motor unit (MU) recruitment to match pre-training torques. The greater acceleration in the b terms by males may reflect sex-related differences in fiber-type area. MMGRMS-torque relationships during a high-intensity contraction provided insight on MU activation strategies following endurance training and between sexes. Furthermore, the findings suggest a relationship between MMGRMS and muscle size.
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10
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Watanabe K, Holobar A, Mita Y, Kouzaki M, Ogawa M, Akima H, Moritani T. Effect of Resistance Training and Fish Protein Intake on Motor Unit Firing Pattern and Motor Function of Elderly. Front Physiol 2018; 9:1733. [PMID: 30564141 PMCID: PMC6288440 DOI: 10.3389/fphys.2018.01733] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2018] [Accepted: 11/16/2018] [Indexed: 12/18/2022] Open
Abstract
We investigated the effect of resistance training and fish protein intake on the motor unit firing pattern and motor function in elderly. Fifty healthy elderly males and females (69.2 ± 4.7 years) underwent 6 weeks of intervention. We applied the leg-press exercise as resistance training and fish protein including Alaska pollack protein (APP) as nutritional supplementation. Subjects were divided into four groups: fish protein intake without resistance training (APP-CN, n = 13), placebo intake without resistance training (PLA-CN, n = 12), fish protein intake with resistance training (APP-RT, n = 12), and placebo intake with resistance training (PLA-RT, n = 13). Motor unit firing rates were calculated from multi-channel surface electromyography by the Convolution Kernel. For the chair-stand test, while significant increases were observed at 6 weeks compared with 0 week in all groups (p < 0.05), significant increases from 0 to 3 weeks and 6 weeks were observed in APP-RT (18.2 ± 1.9 at 0 week to 19.8 ± 2.2 at 3 weeks and 21.2 ± 1.9 at 6 weeks) (p < 0.05). Increase and/or decrease in the motor unit firing rate were mainly noted within motor units with a low-recruitment threshold in APP-RT and PLA-RT at 3 and 6 weeks (12.3 pps at 0 week to 13.6 pps at 3 weeks and 12.1 pps at 6 weeks for APP-RT and 12.9 pps at 0 week to 13.9 pps at 3 weeks and 14.1 pps at 6 weeks for PLA-RT at 50% of MVC) (p < 0.05), but not in APP-CN or PLA-CN (p > 0.05). Time courses of changes in the results of the chair-stand test and motor unit firing rate were different between APP-RT and PLA-RT. These findings suggest that, in the elderly, the effect of resistance training on the motor unit firing rate is observed in motor units with a low-recruitment threshold, and additional fish protein intake modifies these adaptations in motor unit firing patterns and the motor function following resistance training.
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Affiliation(s)
- Kohei Watanabe
- Laboratory of Neuromuscular Biomechanics, School of International Liberal Studies, Chukyo University, Nagoya, Japan
| | - Aleš Holobar
- Faculty of Electrical Engineering and Computer Science, University of Maribor, Maribor, Slovenia
| | - Yukiko Mita
- Department of Human Nutrition, School of Life Studies, Sugiyama Jogakuen University, Nagoya, Japan
| | - Motoki Kouzaki
- Laboratory of Neurophysiology, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, Japan
| | - Madoka Ogawa
- Research Center of Health, Physical Fitness and Sports, Nagoya University, Nagoya, Japan
| | - Hiroshi Akima
- Research Center of Health, Physical Fitness and Sports, Nagoya University, Nagoya, Japan.,Graduate School of Education and Human Development, Nagoya University, Nagoya, Japan
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Colquhoun RJ, Magrini MA, Haun CT, Muddle TWD, Tomko PM, Luera MJ, Mackey CS, Vann CG, Martin JS, Young KC, DeFreitas JM, Roberts MD, Jenkins NDM. Muscle phenotype is related to motor unit behavior of the vastus lateralis during maximal isometric contractions. Physiol Rep 2018. [PMID: 29527830 PMCID: PMC5845862 DOI: 10.14814/phy2.13636] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Previous investigations have reported a relationship between skeletal muscle phenotype and motor unit (MU) firing parameters during submaximal contractions. The purpose of the current investigation, however, was to examine the relationships between motor unit firing behavior during a maximal voluntary contraction, Myosin Heavy Chain (MHC) isoform content, and various molecular neuromuscular targets of the vastus lateralis (VL) muscle in resistance-trained men. Ten resistance-trained males completed a trapezoidal ramp contraction up to 100% of their maximal voluntary isometric strength (MVIC). Surface electromyography was recorded from the VL using a multichannel electrode array and decomposed to examine the firing characteristics of individual MUs. A skeletal muscle biopsy of the VL was also collected from each subject. Regression analyses were performed to identify relationships between type II fiber area and the slopes and/or intercepts of the mean firing rate (FRMEAN ) versus recruitment threshold (RT), max firing rate (FRMAX ) versus RT, and RT versus MU action potential amplitude (MUAPPP ) relationships. There were significant inverse relationships between type II fiber area and the y-intercept of the FR versus RT relationship (P < 0.05). Additionally, strong relationships (r > 0.5) were found between type II fiber area and FRMEAN versus RT slope and RT versus MUAPPP slope and intercept. These data further support the hypothesis that skeletal muscle phenotype is related to MU behavior during isometric contraction. However, our data, in concert with previous investigations, may suggest that these relationships are influenced by the intensity of the contraction.
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Affiliation(s)
- Ryan J Colquhoun
- Applied Neuromuscular Physiology Laboratory, Oklahoma State University, Stillwater, Oklahoma
| | - Mitchel A Magrini
- Applied Neuromuscular Physiology Laboratory, Oklahoma State University, Stillwater, Oklahoma
| | - Cody T Haun
- Molecular and Applied Sciences Laboratory, Auburn University, Auburn, Alabama
| | - Tyler W D Muddle
- Applied Neuromuscular Physiology Laboratory, Oklahoma State University, Stillwater, Oklahoma
| | - Patrick M Tomko
- Applied Neuromuscular Physiology Laboratory, Oklahoma State University, Stillwater, Oklahoma
| | - Micheal J Luera
- Applied Neuromuscular Physiology Laboratory, Oklahoma State University, Stillwater, Oklahoma
| | - Cameron S Mackey
- Applied Neuromuscular Physiology Laboratory, Oklahoma State University, Stillwater, Oklahoma
| | - Christopher G Vann
- Molecular and Applied Sciences Laboratory, Auburn University, Auburn, Alabama
| | - Jeffrey S Martin
- Department of Cell Biology and Physiology, Edward Via College of Osteopathic Medicine - Auburn Campus, Auburn, Alabama
| | - Kaelin C Young
- Department of Cell Biology and Physiology, Edward Via College of Osteopathic Medicine - Auburn Campus, Auburn, Alabama
| | - Jason M DeFreitas
- Applied Neuromuscular Physiology Laboratory, Oklahoma State University, Stillwater, Oklahoma
| | - Michael D Roberts
- Molecular and Applied Sciences Laboratory, Auburn University, Auburn, Alabama
| | - Nathaniel D M Jenkins
- Applied Neuromuscular Physiology Laboratory, Oklahoma State University, Stillwater, Oklahoma
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12
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Trevino MA, Herda TJ, Fry AC, Gallagher PM, Vardiman JP, Mosier EM, Miller JD. Influence of the contractile properties of muscle on motor unit firing rates during a moderate-intensity contraction in vivo. J Neurophysiol 2016; 116:552-62. [PMID: 27146989 PMCID: PMC4978784 DOI: 10.1152/jn.01021.2015] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2015] [Accepted: 05/02/2016] [Indexed: 11/22/2022] Open
Abstract
It is suggested that firing rate characteristics of motor units (MUs) are influenced by the physical properties of the muscle. However, no study has correlated MU firing rates at recruitment, targeted force, or derecruitment with the contractile properties of the muscle in vivo. Twelve participants (age = 20.67 ± 2.35 yr) performed a 40% isometric maximal voluntary contraction of the leg extensors that included linearly increasing, steady force, and decreasing segments. Muscle biopsies were collected with myosin heavy chain (MHC) content quantified, and surface electromyography (EMG) was recorded from the vastus lateralis. The EMG signal was decomposed into the firing events of single MUs. Slopes and y-intercepts were calculated for 1) firing rates at recruitment vs. recruitment threshold, 2) mean firing rates at steady force vs. recruitment threshold, and 3) firing rates at derecruitment vs. derecruitment threshold relationships for each subject. Correlations among type I %MHC isoform content and the slopes and y-intercepts from the three relationships were examined. Type I %MHC isoform content was correlated with MU firing rates at recruitment (y-intercepts: r = -0.577; slopes: r = 0.741) and targeted force (slopes: r = 0.853) vs. recruitment threshold and MU firing rates at derecruitment (y-intercept: r = -0.597; slopes: r = 0.701) vs. derecruitment threshold relationships. However, the majority of the individual MU firing rates vs. recruitment and derecruitment relationships were not significant (P > 0.05) and, thus, revealed no systematic pattern. In contrast, MU firing rates during the steady force demonstrated a systematic pattern with higher firing rates for the lower- than higher-threshold MUs and were correlated with the physical properties of MUs in vivo.
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Affiliation(s)
| | - Trent J Herda
- Neuromechanics Laboratory, University of Kansas, Lawrence, Kansas;
| | - Andrew C Fry
- Applied Physiology Laboratory, University of Kansas, Lawrence, Kansas; and
| | - Philip M Gallagher
- Applied Physiology Laboratory, University of Kansas, Lawrence, Kansas; and
| | - John P Vardiman
- Applied Physiology and Sports Medicine Laboratory, Kansas State University, Manhattan, Kansas
| | - Eric M Mosier
- Neuromechanics Laboratory, University of Kansas, Lawrence, Kansas
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