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Herda TJ, Holmes EA, Cleary CJ, Minor KT, Thyfault JP, Shook RP, Herda AA. Motor unit firing rates increase in prepubescent youth following linear periodization resistance exercise training. Eur J Appl Physiol 2024; 124:2675-2686. [PMID: 38634901 DOI: 10.1007/s00421-024-05455-w] [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: 10/11/2023] [Accepted: 02/29/2024] [Indexed: 04/19/2024]
Abstract
PURPOSE The purpose was to examine the effects of 8-weeks (3 days/week) of linear periodization resistance exercise training (RET) on neuromuscular function in prepubescent youth. METHODS Twenty-five healthy prepubescent youth (11 males, 14 females, age = 9.1 ± 0.8 years) completed the RET (n = 17) or served as controls (CON, n = 8). Isometric maximal voluntary contractions (MVCs) and trapezoidal submaximal contractions at 35 and 60% MVC of the right leg extensors were performed with surface electromyography (EMG) recorded from the leg extensors [vastus lateralis (VL), rectus femoris, and vastus medialis] and flexors (biceps femoris and semitendinosus). EMG amplitude of the leg extensors and flexors were calculated during the MVCs. Motor unit (MU) action potential trains were decomposed from the surface EMG of the VL for the 35 and 60% MVCs. MU firing rates and action potential amplitudes were regressed against recruitment threshold with the y-intercepts and slopes calculated for each contraction. Total leg extensor muscle cross-sectional area (CSA) was collected using ultrasound images. ANOVA models were used to examine potential differences. RESULTS Isometric strength increased post-RET (P = 0.006) with no changes in leg extensor and flexor EMG amplitude. Furthermore, there were no changes in total CSA or the MU action potential amplitude vs. recruitment threshold relationships. However, there were increases in the firing rates of the higher-threshold MUs post-RET as indicated with greater y-intercepts (P = 0.003) from the 60% MVC and less negative slope (P = 0.004) of the firing rates vs. recruitment threshold relationships at 35% MVC. CONCLUSIONS MU adaptations contribute to strength increases following RET in prepubescent youth.
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Affiliation(s)
- Trent J Herda
- Department of Health, Sport, and Exercise Science, University of Kansas, 1301 Sunnyside Avenue, Room 101BE, Lawrence, 66045, KS, USA.
- Center for Children's Healthy Lifestyle and Nutrition, Kansas City, MO, USA.
| | - Elizabeth A Holmes
- Department of Health, Sport, and Exercise Science, University of Kansas, 1301 Sunnyside Avenue, Room 101BE, Lawrence, 66045, KS, USA
| | - Christopher J Cleary
- Department of Health, Sport, and Exercise Science, University of Kansas-Edwards Campus, Overland Park, KS, USA
| | - Kelsey T Minor
- Department of Health, Sport, and Exercise Science, University of Kansas, 1301 Sunnyside Avenue, Room 101BE, Lawrence, 66045, KS, USA
| | - John P Thyfault
- Department of Cell Biology and Physiology and Internal Medicine, University of Kansas Medical Center, Kansas City, KS, USA
- Center for Children's Healthy Lifestyle and Nutrition, Kansas City, MO, USA
| | - Robin P Shook
- Department of Pediatrics, Children's Mercy Hospital, Kansas City, MO, USA
- Center for Children's Healthy Lifestyle and Nutrition, Kansas City, MO, USA
| | - Ashley A Herda
- Department of Health, Sport, and Exercise Science, University of Kansas-Edwards Campus, Overland Park, KS, USA
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Wohlgemuth KJ, Conner MJ, Tinsley GM, Palmer TB, Mota JA. Strategies for Improving Firefighter Health On-Shift: A Review. J Funct Morphol Kinesiol 2024; 9:105. [PMID: 38921641 PMCID: PMC11204757 DOI: 10.3390/jfmk9020105] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/14/2024] [Revised: 06/11/2024] [Accepted: 06/13/2024] [Indexed: 06/27/2024] Open
Abstract
The fire service suffers from high rates of cardiovascular disease and poor overall health, and firefighters often suffer fatal and non-fatal injuries while on the job. Most fatal injuries result from sudden cardiac death, while non-fatal injuries are to the musculoskeletal system. Previous works suggest a mechanistic link between several health and performance variables and injury risk. In addition, studies have suggested physical activity and nutrition can improve overall health and occupational performance. This review offers practical applications for exercise via feasible training modalities as well as nutritional recommendations that can positively impact performance on the job. Time-efficient training modalities like high-intensity interval training and feasible modalities such as resistance training offer numerous benefits for firefighters. Also, modifying and supplementing the diet and can be advantageous for health and body composition in the fire service. Firefighters have various schedules, making it difficult for planned exercise and eating while on shift. The practical training and nutritional aspects discussed in this review can be implemented on-shift to improve the overall health and performance in firefighters.
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Affiliation(s)
- Kealey J. Wohlgemuth
- Neuromuscular and Occupational Performance Laboratory, Texas Tech University, Lubbock, TX 79409, USA;
| | | | - Grant M. Tinsley
- Energy Balance and Body Composition Laboratory, Texas Tech University, Lubbock, TX 79409, USA;
| | - Ty B. Palmer
- Muscular Assessment Laboratory, Texas Tech University, Lubbock, TX 79409, USA;
| | - Jacob A. Mota
- Neuromuscular and Occupational Performance Laboratory, Texas Tech University, Lubbock, TX 79409, USA;
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3
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Sherman DA, Rush J, Stock MS, D. Ingersoll C, E. Norte G. Neural drive and motor unit characteristics after anterior cruciate ligament reconstruction: implications for quadriceps weakness. PeerJ 2023; 11:e16261. [PMID: 37818333 PMCID: PMC10561646 DOI: 10.7717/peerj.16261] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2023] [Accepted: 09/18/2023] [Indexed: 10/12/2023] Open
Abstract
Purpose The purpose of this investigation was to compare the quality of neural drive and recruited quadriceps motor units' (MU) action potential amplitude (MUAPAMP) and discharge rate (mean firing rate (MFR)) relative to recruitment threshold (RT) between individuals with anterior cruciate ligament reconstruction (ACLR) and controls. Methods Fourteen individuals with ACLR and 13 matched controls performed trapezoidal knee extensor contractions at 30%, 50%, 70%, and 100% of their maximal voluntary isometric contraction (MVIC). Decomposition electromyography (dEMG) and torque were recorded concurrently. The Hoffmann reflex (H-reflex) and central activation ratio (CAR) were acquired bilaterally to detail the proportion of MU pool available and volitionally activated. We examined MUAPAMP-RT and MFR-RT relationships with linear regression and extracted the regression line slope, y-intercept, and RT range for each contraction. Linear mixed effect modelling used to analyze the effect of group and limb on regression line slope and RT range. Results Individuals with ACLR demonstrated lower MVIC torque in the involved limb compared to uninvolved limb. There were no differences in H-reflex or CAR between groups or limbs. The ACLR involved limb demonstrated smaller mass-normalized RT range and slower MU firing rates at high contraction intensities (70% and 100% MVIC) compared to uninvolved and control limbs. The ACLR involved limb also demonstrated larger MU action potentials in the VM compared to the contralateral limb. These differences were largely attenuated with relative RT normalization. Conclusions These results suggest that persistent strength deficits following ACLR may be attributable to a diminished quadriceps motor neuron pool and inability to upregulate the firing rate of recruited MUs.
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Affiliation(s)
- David A. Sherman
- Live4 Physical Therapy and Wellness, Acton, Massachusetts, United States of America
- Chobanian & Avedisian School of Medicine, Boston University, Boston, Massachusetts, United States of America
- Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States of America
| | - Justin Rush
- Division of Physical Therapy, School of Rehabilitation and Communication Sciences, College of Health Sciences and Professions, Ohio University, Athens, Ohio, United States of America
| | - Matt S. Stock
- Cognition, Neuroplasticity, & Sarcopenia (CNS) Lab, Institute of Exercise Physiology and Rehabilitation Science, University of Central Florida, Orlando, FL, United States of America
| | - Christopher D. Ingersoll
- College of Health Professions and Sciences, School of Kinesiology and Rehabilitation Sciences, University of Central Florida, Orlando, Florida, United States of America
| | - Grant E. Norte
- Cognition, Neuroplasticity, & Sarcopenia (CNS) Lab, Institute of Exercise Physiology and Rehabilitation Science, University of Central Florida, Orlando, FL, United States of America
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Wilson MT, Hunter AM, Fairweather M, Kerr S, Hamilton DL, Macgregor LJ. Enhanced skeletal muscle contractile function and corticospinal excitability precede strength and architectural adaptations during lower-limb resistance training. Eur J Appl Physiol 2023; 123:1911-1928. [PMID: 37185932 PMCID: PMC10460716 DOI: 10.1007/s00421-023-05201-8] [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: 10/28/2022] [Accepted: 04/06/2023] [Indexed: 05/17/2023]
Abstract
PURPOSE Evolving investigative techniques are providing greater understanding about the early neuromuscular responses to resistance training among novice exercisers. The aim of this study was to investigate the time-course of changes in muscle contractile mechanics, architecture, neuromuscular, and strength adaptation during the first 6-weeks of lower-limb resistance training. METHODS Forty participants: 22 intervention (10 males/12 females; 173.48 ± 5.20 cm; 74.01 ± 13.13 kg) completed 6-week resistance training, and 18 control (10 males/8 females; 175.52 ± 7.64 cm; 70.92 ± 12.73 kg) performed no resistance training and maintained their habitual activity. Radial muscle displacement (Dm) assessed via tensiomyography, knee extension maximal voluntary contraction (MVC), voluntary activation (VA), corticospinal excitability and inhibition via transcranial magnetic stimulation, motor unit (MU) firing rate, and muscle thickness and pennation angle via ultrasonography were assessed before and after 2, 4, and 6-weeks of dynamic lower-limb resistance training or control. RESULTS After 2-weeks training, Dm reduced by 19-25% in the intervention group; this was before any changes in neural or morphological measures. After 4-weeks training, MVC increased by 15% along with corticospinal excitability by 16%; however, there was no change in VA, corticospinal inhibition, or MU firing rate. After 6-weeks training there was further MVC increase by 6% along with muscle thickness by 13-16% and pennation angle by 13-14%. CONCLUSION Enhanced contractile properties and corticospinal excitability occurred before any muscle architecture, neural, and strength adaptation. Later increases in muscular strength can be accounted for by architectural adaptation.
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Affiliation(s)
- Matthew T Wilson
- Physiology, Exercise, and Nutrition Research Group, Faculty of Health Sciences and Sport, University of Stirling, Stirling, UK
| | - Angus M Hunter
- Physiology, Exercise, and Nutrition Research Group, Faculty of Health Sciences and Sport, University of Stirling, Stirling, UK.
- Department of Sports Sciences, School of Science and Technology, Nottingham Trent University, Nottingham, NG11 8NS, UK.
| | | | - Stewart Kerr
- Life Fit Wellness, Healthcare & Exercise Centre, Falkirk, Scotland, UK
| | - D Lee Hamilton
- Faculty of Health, School of Exercise and Nutrition Sciences, Institute for Physical Activity and Nutrition (IPAN), Deakin University, Geelong, Australia
| | - Lewis J Macgregor
- Physiology, Exercise, and Nutrition Research Group, Faculty of Health Sciences and Sport, University of Stirling, Stirling, UK
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Orantes-Gonzalez E, Heredia-Jimenez J, Lindley SB, Richards JD, Chapman GJ. An exploration of the motor unit behaviour during the concentric and eccentric phases of a squat task performed at different speeds. Sports Biomech 2023:1-12. [PMID: 37339268 DOI: 10.1080/14763141.2023.2221682] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/17/2022] [Accepted: 05/31/2023] [Indexed: 06/22/2023]
Abstract
Despite squatting being important in strength training and rehabilitation, few studies have investigated motor unit (MU) behaviour. This study explored the MU behaviour of vastus medialis (VM) and vastus lateralis (VL) during the concentric and eccentric phases of a squat exercise performed at two speeds. Twenty-two participants had surface dEMG sensors attached over VM and VL, and IMUs recorded thigh and shank angular velocities. Participants performed squats at 15 and 25 repetitions per minute in a randomised order, and EMG signals were decomposed into their MU action potential trains. A four factor (muscle × speed × contraction phase × sexes) mixed methods ANOVA revealed significant main effects for MU firing rates between speeds, between muscles and between sexes, but not contraction phases. Post hoc analysis showed significantly greater MU firing rates and amplitudes in VM. A significant interaction was seen between speed and the contraction phases. Further analysis revealed significantly greater firing rates during the concentric compared to the eccentric phases, and between speeds during the eccentric phase only. VM and VL respond differently during squatting depending on speed and contraction phase. These new insights in VM and VL MU behvaviour may be useful when designing training and rehabilitation protocols.
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Affiliation(s)
- Eva Orantes-Gonzalez
- Department of Sports and Computer Science, Faculty of Sports, University of Pablo de Olavide, Seville, Spain
| | - Jose Heredia-Jimenez
- Department of Physical Education and Sport, Faculty of Education, Economy and Technology, University of Granada, Ceuta, Spain
| | | | - Jim D Richards
- Allied Health Research Unit, University of Central Lancashire, Preston, UK
| | - Graham J Chapman
- Allied Health Research Unit, University of Central Lancashire, Preston, UK
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Schilaty ND, McPherson AL, Nagai T, Bates NA. Arthrogenic muscle inhibition manifests in thigh musculature motor unit characteristics after anterior cruciate ligament injury. Eur J Sport Sci 2023; 23:840-850. [PMID: 35306977 PMCID: PMC9626399 DOI: 10.1080/17461391.2022.2056520] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Joint trauma induces a presynaptic reflex inhibition termed arthrogenic muscle inhibition (AMI) that prevents complete activation of muscles. Reduced motor unit (MU) output is a hypothesised mechanism for persistent strength deficits. The objective of this study was to determine MU characteristics of thigh musculature and determine how they change with anterior cruciate ligament (ACL) injury compared to healthy controls. A randomised protocol of knee flexion/extension isometric contractions (10-50% maximal voluntary isometric contraction) was performed for each leg with surface EMG 5-pin array electrodes placed on the vastus medialis, vastus lateralis, semitendinosus and biceps femoris. Longitudinal assessments for average rate coding, recruitment thresholds and MU action potentials were acquired at 6-month intervals. With exception of the vastus medialis, all thigh musculature of ACL-injured demonstrated smaller MU action potential peak-to-peak amplitude. For average rate coding, ACL-injured demonstrated lower coding rates than Controls for the quadriceps (p < .05) and higher rates than Controls for the hamstrings (p < .05). These MU characteristics were different from Controls after ACL reconstruction up to 12 months post-surgery, yet maximal strength increased during this time frame. As thigh MU characteristics are known across phases of ACL rehabilitation, future studies can assess these patterns of motor control and their potential to determine risk of re-injury. Further, future rehabilitation can target specific intervention programmes to restore motor control.HighlightsMotor unit strategies of arthrogenic muscle inhibition are characterised for the first time via decomposed EMG.Motor unit deficits of thigh musculature persist throughout all phases of ACL rehabilitation, even after return-to-sport.After ACL injury, motor unit sizes at similar recruitment thresholds were smaller than those of healthy controls.
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Affiliation(s)
- Nathan D. Schilaty
- Department of Neurosurgery & Brain Repair, University of South Florida, Tampa, FL, USA
- Center for Neuromusculoskeletal Research, University of South Florida, Tampa, FL, USA
- Department of Orthopedics, Mayo Clinic, Rochester, MN, USA
| | - April L. McPherson
- Department of Orthopedics, Mayo Clinic, Rochester, MN, USA
- United States Olympic & Paralympic Committee, Colorado Springs, CO, USA
| | - Takashi Nagai
- Department of Orthopedics, Mayo Clinic, Rochester, MN, USA
- United States Army Research Institute of Environmental Medicine, Natick, MA, USA
| | - Nathaniel A. Bates
- Department of Orthopedics, Mayo Clinic, Rochester, MN, USA
- Department of Orthopaedics, The Ohio State University, Columbus, OH, 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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MacLennan RJ, Mota JA, Thompson BJ, Stock MS. Effects of Strength and Conditioning on Maximal Isometric Strength, Motor Unit Behavior, and Concentric Isokinetic Peak Torque in Middle-School Boys'. J Strength Cond Res 2022; 36:1318-1326. [PMID: 33780394 DOI: 10.1519/jsc.0000000000003643] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
ABSTRACT MacLennan, RJ, Mota, JA, Thompson, BJ, and Stock, MS. Effects of strength and conditioning on maximal isometric strength, motor unit behavior, and concentric isokinetic peak torque in middle-school boys. J Strength Cond Res 36(5): 1318-1326, 2022-It has long been theorized that improvements in muscle strength in young athletes are mediated by motor unit adaptations. The ability to decompose surface electromyographic signals obtained during isometric contractions now allow for such research questions to be answered. We examined changes in isometric and concentric isokinetic strength, as well as vastus lateralis motor unit behavior, after 16 weeks of strength training and conditioning in middle-school aged boys. Nine boys (mean ± SD age = 12 ± 1 years) participated in training. Five boys (age = 13 ± 1 years) served as control subjects. The training subjects performed 90 minutes of high-intensity, multi-joint exercise twice per week. Assessments of unilateral maximal voluntary isometric contraction (MVIC) force of the knee extensors, concentric peak torque at velocities of 60, 180, and 300°·s-1, and vastus lateralis motor unit data during 50 and 80% MVIC tests were performed. Strength training and conditioning did not improve MVIC force. Greater training-induced strength increases were observed at faster isokinetic velocities, with a large effect size at 300°·s-1 (d = 0.813). The slopes and y-intercepts of the mean firing rate vs. recruitment threshold relationship and the action potential amplitude vs. recruitment threshold relationship were unaffected by training. Sixteen weeks of middle-school strength and conditioning did not enhance maximal isometric strength or vastus lateralis motor unit control, but improvements were observed during rapid isokinetic muscle actions. Given the lack of training (multi-joint) vs. testing (single-joint) specificity, we propose that motor unit adaptations in youth are task specific.
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Affiliation(s)
- Rob J MacLennan
- School of Kinesiology and Physical Therapy, University of Central Florida, Orlando, Florida
| | - Jacob A Mota
- Department of Exercise and Sport Science, University of North Carolina-Chapel Hill, Chapel Hill, North Carolina
| | | | - Matt S Stock
- School of Kinesiology and Physical Therapy, University of Central Florida, Orlando, Florida
- Institute of Exercise Physiology and Rehabilitation Science, University of Central Florida, Orlando, Florida
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Schilaty ND, Savoldi F, Nasr Z, Weinshenker BG. Neuromotor control associates with muscle weakness observed with McArdle sign of multiple sclerosis. Ann Clin Transl Neurol 2022; 9:515-528. [PMID: 35289110 PMCID: PMC8994990 DOI: 10.1002/acn3.51526] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2021] [Revised: 01/20/2022] [Accepted: 02/05/2022] [Indexed: 11/07/2022] Open
Abstract
OBJECTIVE Multiple Sclerosis (MS) is often accompanied by myelopathy, which may be associated with progressive worsening. A specific finding of MS-associated myelopathy is McArdle sign, wherein neck flexion is associated with prominent increased limb weakness relative to that detected with neck extension. In this study, we characterized neuromotor control properties of finger extensors in association with the McArdle sign. METHODS A custom-built device was utilized to monitor torque production of the wrist extensors with simultaneous recording of surface electromyography of the extensor digitorum. The electromyography was decomposed and analyzed via both linear and nominal regressions. RESULTS Linear regressions demonstrated a strong difference between groups for MS from healthy controls and other myelopathies for motor unit action potential amplitude and average firing rate (p < 0.001). Further, linear regression demonstrated good correlations of neuromotor variables to mechanical torque output (0.24 ≤ R2 ≤ 0.76). Nominal regression distinguished MS from healthy controls with an AUC of 0.87, specificity of 0.97, and sensitivity of 0.64. Nominal regression of MS from other myelopathies demonstrated an AUC of 0.88, specificity of 0.85, and sensitivity of 0.79. INTERPRETATION These data demonstrate the neuromotor control factors that largely determine muscle force production change with the observation of McArdle sign; these neuromotor control factors can differentiate MS from both healthy controls and other myelopathy conditions.
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Affiliation(s)
- Nathan D Schilaty
- Department of Neurosurgery & Brain Repair, University of South Florida, Tampa, Florida, USA.,Center for Neuromusculoskeletal Research, University of South Florida, Tampa, Florida, USA
| | - Filippo Savoldi
- Department of Neurology, Mayo Clinic, Rochester, Minnesota, USA
| | - Zahra Nasr
- Department of Neurology, Mayo Clinic, Rochester, Minnesota, USA
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Elgueta-Cancino E, Evans E, Martinez-Valdes E, Falla D. The Effect of Resistance Training on Motor Unit Firing Properties: A Systematic Review and Meta-Analysis. Front Physiol 2022; 13:817631. [PMID: 35295567 PMCID: PMC8918924 DOI: 10.3389/fphys.2022.817631] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2021] [Accepted: 01/24/2022] [Indexed: 11/13/2022] Open
Abstract
While neural changes are thought to be responsible for early increases in strength following resistance training (RT), the exact changes in motor unit (MU) firing properties remain unclear. This review aims to synthesize the available evidence on the effect of RT on MU firing properties. MEDLINE (OVID interface), EMBASE (OVID interface), Web of Science (all databases), Cochrane Library, EBSCO CINAHL Plus, PubMed, and EBSCO SportDiscus were searched from inception until June 2021. Randomized controlled trials and non-randomized studies of interventions that compared RT to no intervention (control) were included. Two reviewers independently extracted data from each trial, assessed the risk of bias and rated the cumulative quality of evidence. Motor unit discharge rate (MUDR), motor unit recruitment threshold (MURT), motor unit discharge rate variability (MUDRV), MU discharge rate at recruitment vs. recruitment threshold relationship, and MU discharge rate vs. recruitment threshold relationship were assessed. Seven trials including 167 participants met the inclusion criteria. Meta-analysis (four studies) revealed that MUDR did not change significantly (P = 0.43), but with considerable heterogeneity likely to be present (I 2 = 91). Low to moderate evidence supports changes in MUDRV, MUDR at recruitment vs. recruitment threshold relationship, and the MUDR vs. recruitment threshold relationship. Overall, this systematic review revealed that there is a lack of high-quality evidence for the effect of RT on MU firing properties. Heterogeneity across studies undermines the quality of the evidence for multiple outcomes and affects the conclusions that can be drawn.
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Affiliation(s)
| | | | | | - Deborah Falla
- Centre of Precision Rehabilitation for Spinal Pain (CPR Spine), School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, United Kingdom
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Dimmick HL, Trevino MA, Miller JD, Parra ME, Sterczala AJ, Herda TJ. Method of analysis influences interpretations of sex-related differences in firing rates during prolonged submaximal isometric contractions. JOURNAL OF MUSCULOSKELETAL & NEURONAL INTERACTIONS 2022; 22:27-36. [PMID: 35234156 PMCID: PMC8919653] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
OBJECTIVE This study examined motor unit (MU) firing rates during a prolonged isometric contraction of the vastus lateralis (VL) for females and males. METHODS Surface electromyographic (sEMG) signals were recorded from the VL for eleven females and twelve males during a 45-second isometric trapezoid muscle actions at 40% of maximal voluntary contraction (MVC). For each MU, mean firing rate (MFR) was calculated for the initial and final 10-second epochs of the steady torque segment and regressed against recruitment threshold (RT, expressed as %MVC), as well as time at recruitment (TREC, seconds). MFR was also averaged for each subject. RESULTS Significant differences existed across epochs for the y-intercepts (P=0.009) of the MFR vs. TREC relationship, as well as the grouped MFR analysis (P<0.001); no differences were observed between epochs for the MFR vs. RT relationship. Significant differences existed between sexes for the grouped MFR analysis (P=0.049), but no differences were observed for the MFR vs. TREC or MFR vs. RT relationships. CONCLUSION Analysis method may impact interpretation of firing rate behavior; increases in MU firing rates across a prolonged isometric contraction were observed in the MFR vs. TREC relationship and the grouped MFR analysis.
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Affiliation(s)
- Hannah L. Dimmick
- Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Calgary, AB, Canada
| | - Michael A. Trevino
- Applied Neuromuscular Physiology Laboratory Department of Health and Human Performance, Oklahoma State University, Stillwater, OK, USA
| | - Jonathan D. Miller
- Neuromechanics Laboratory, Department of Health, Sport and Exercise Sciences, University of Kansas, Lawrence, KS, USA
| | - Mandy E. Parra
- Mayborn College of Health Sciences, University of Mary Hardin-Baylor, Belton, TX, USA
| | - Adam J. Sterczala
- Neuromuscular Research Laboratory, Department of Sports Medicine and Nutrition, University of Pittsburg, Pittsburgh, PA, USA
| | - Trent J. Herda
- Neuromechanics Laboratory, Department of Health, Sport and Exercise Sciences, University of Kansas, Lawrence, KS, USA,Corresponding author: Trent J. Herda, Associate Professor, Neuromechanics Laboratory, Department of Health, Sport and Exercise Sciences, University of Kansas, 1301 Sunnyside Avenue, Room 101BE, Lawrence, KS 66045 E-mail:
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12
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Aagaard P, Bojsen-Møller J, Lundbye-Jensen J. Assessment of Neuroplasticity With Strength Training. Exerc Sport Sci Rev 2020; 48:151-162. [DOI: 10.1249/jes.0000000000000229] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
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13
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Sterczala AJ, Miller JD, Dimmick HL, Wray ME, Trevino MA, Herda TJ. Eight weeks of resistance training increases strength, muscle cross-sectional area and motor unit size, but does not alter firing rates in the vastus lateralis. Eur J Appl Physiol 2019; 120:281-294. [DOI: 10.1007/s00421-019-04273-9] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2019] [Accepted: 11/23/2019] [Indexed: 12/11/2022]
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Harmon KK, Girts RM, MacLennan RJ, Stock MS. Is the motor unit mean firing rate versus recruitment threshold relationship linear? Physiol Meas 2019; 40:095002. [PMID: 31470424 DOI: 10.1088/1361-6579/ab4025] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Advances in surface electromyographic (EMG) signal decomposition allow researchers to analyze data for 20-50 motor units per contraction. To simplify interpretation, some investigators rely on group mean analysis of the mean firing rate versus recruitment threshold relationship, but it is unclear if this association is linear. OBJECTIVE To determine whether this relationship is strongest when analyzed via linear, quadratic, or cubic regression. APPROACH Twenty-one men (mean ± SD age = 24 ± 4 years) and 16 women (21 ± 2 years) performed isometric contractions of the knee extensors at 50% of maximal force while bipolar surface EMG signals were recorded from the vastus lateralis. A decomposition algorithm was used to calculate the mean firing rate and recruitment threshold of each motor unit at accuracy levels ranging from 90.0%-93.0%. Polynominal regression was used to determine if each relationship was best fit with a linear, quadratic, or cubic model. We examined individual contractions and grouped data. MAIN RESULTS Overall, 80% of the relationships were best fit with a linear model. Quadratic and cubic relationships were more appropriate for 16% and 2% of the contractions, respectively. Selecting varying accuracy levels within a range of 90.0%-93.0% had little influence on whether a given dataset was best fit with a linear, quadratic, or cubic model. Grouping of data provided different relationships than otherwise found on a contraction-by-contraction basis. SIGNIFICANCE The mean firing rate versus recruitment threshold relationship is typically best fit with a linear model. These relationships should be examined on an individual contraction basis.
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Affiliation(s)
- Kylie K Harmon
- Neuromuscular Plasticity Laboratory, School of Kinesiology and Physical Therapy, University of Central Florida, 12354 Research Parkway, Orlando, FL, 32826, United States of America
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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: 176] [Impact Index Per Article: 35.2] [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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Sterczala AJ, Miller JD, Trevino MA, Dimmick HL, Herda TJ. Differences in the motor unit firing rates and amplitudes in relation to recruitment thresholds during submaximal contractions of the first dorsal interosseous between chronically resistance-trained and physically active men. Appl Physiol Nutr Metab 2018; 43:759-768. [PMID: 29481763 DOI: 10.1139/apnm-2017-0646] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Previous investigations report no changes in motor unit (MU) firing rates during submaximal contractions following resistance training. These investigations did not account for MU recruitment or examine firing rates as a function of recruitment threshold (REC). Therefore, MU recruitment and firing rates in chronically resistance-trained (RT) and physically active controls (CON) were examined. Surface electromyography signals were collected from the first dorsal interosseous during isometric muscle actions at 40% and 70% maximal voluntary contraction (MVC). For each MU, force at REC, mean firing rate (MFR) during the steady force, and MU action potential amplitude (MUAPAMP) were analyzed. For each individual and contraction, the MFRs were linearly regressed against REC, whereas, exponential models were applied to the MFR versus MUAPAMP and MUAPAMP versus REC relationships with the y-intercepts and slopes (linear) and A and B terms (exponential) calculated. For the 40% MVC, the RT had less negative slopes (p = 0.001) and lower y-intercepts (p = 0.006) of the MFR versus REC relationships and lower B terms (p = 0.011) of the MUAPAMP versus REC relationships. There were no differences in either relationship between groups for the 70% MVC. During the 40% MVC, the RT had a smaller range of MFRs and MUAPAMPS in comparison with the CON, likely because of reduced MU recruitment. The RT had lower MFRs and recruitment during the 40% MVC, which may indicate a leftward shift in the force-frequency relationship, and thus require less excitation to the motoneuron pool to match the same relative force.
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Affiliation(s)
- Adam J Sterczala
- a Neuromechanics Laboratory, Department of Health, Sport and Exercise Sciences, University of Kansas, Lawrence, KS 66045, USA
| | - Jonathan D Miller
- a Neuromechanics Laboratory, Department of Health, Sport and Exercise Sciences, University of Kansas, Lawrence, KS 66045, USA
| | - Michael A Trevino
- b Department of Health Sciences, Armstrong State University, Savannah, GA 31419, USA
| | - Hannah L Dimmick
- a Neuromechanics Laboratory, Department of Health, Sport and Exercise Sciences, University of Kansas, Lawrence, KS 66045, USA
| | - Trent J Herda
- a Neuromechanics Laboratory, Department of Health, Sport and Exercise Sciences, University of Kansas, Lawrence, KS 66045, USA
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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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18
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Interplay between body stabilisation and quadriceps muscle activation capacity. J Electromyogr Kinesiol 2017; 34:44-49. [DOI: 10.1016/j.jelekin.2017.03.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2016] [Revised: 10/30/2016] [Accepted: 03/10/2017] [Indexed: 11/22/2022] Open
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Herda TJ, Miller JD, Trevino MA, Mosier EM, Gallagher PM, Fry AC, Vardiman JP. The change in motor unit firing rates at de-recruitment relative to recruitment is correlated with type I myosin heavy chain isoform content of the vastus lateralis in vivo. Acta Physiol (Oxf) 2016; 216:454-63. [PMID: 26513624 DOI: 10.1111/apha.12624] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2015] [Revised: 08/26/2015] [Accepted: 10/28/2015] [Indexed: 11/30/2022]
Abstract
AIM To investigate the change in motor unit (MU) firing rates (FR) at de-recruitment relative to recruitment and the relation to % type I myosin heavy chain isoform content (type I %MHC) of the vastus lateralis (VL) in vivo. METHODS Ten subjects performed a 22-s submaximal isometric trapezoid muscle action that included a linearly increasing, steady force at 50% maximal voluntary contraction, and linearly decreasing segments. Surface electromyographic signals were collected from the VL and were decomposed into constituent MU action potentials trains. A tissue sample from the VL was taken to calculate type I %MHC. The y-intercepts and slopes were calculated for the changes (Δ) in FR at de-recruitment (FRDEREC ) relative to FR at recruitment (FRREC ) vs. FRREC relationship for each subject. Correlations were performed between the y-intercepts and slopes with type I %MHC. RESULTS The majority of MUs had greater FRDEREC than FRREC . The y-intercepts (r = -0.600, P = 0.067) were not significantly correlated, but the slopes (r = -0.793, P = 0.006) were significantly correlated with type I %MHC. CONCLUSION The majority of the motoneuron pool had greater FRDEREC than FRREC , however, individuals with higher type I %MHC had a greater propensity to have MUs with FRREC > FRDEREC as indicated by the slope values. Overall, the contractile properties of the muscle (MHC) could partially explain the differences in MU firing rates at de-recruitment relative to recruitment. Thus, suggesting the fatigability of the muscle influences the alterations in MU firing rates from recruitment to de-recruitment.
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Affiliation(s)
- T. J. Herda
- Neuromechanics Laboratory; Department of Health, Sport and Exercise Sciences; University of Kansas; Lawrence KS USA
| | - J. D. Miller
- Neuromechanics Laboratory; Department of Health, Sport and Exercise Sciences; University of Kansas; Lawrence KS USA
| | - M. A. Trevino
- Neuromechanics Laboratory; Department of Health, Sport and Exercise Sciences; University of Kansas; Lawrence KS USA
| | - E. M. Mosier
- Neuromechanics Laboratory; Department of Health, Sport and Exercise Sciences; University of Kansas; Lawrence KS USA
| | - P. M. Gallagher
- Applied Physiology Laboratory; Department of Health Sport and Exercise Sciences; University of Kansas; Lawrence KS USA
| | - A. C. Fry
- Neuromechanics Laboratory; Department of Health, Sport and Exercise Sciences; University of Kansas; Lawrence KS USA
| | - J. P. Vardiman
- Applied Physiology Laboratory; Department of Health Sport and Exercise Sciences; University of Kansas; Lawrence KS USA
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Ye X, Beck TW, Wages NP. Influence of prolonged static stretching on motor unit firing properties. Muscle Nerve 2016; 53:808-17. [DOI: 10.1002/mus.24913] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/15/2015] [Indexed: 11/09/2022]
Affiliation(s)
- Xin Ye
- Biophysics Laboratory, Department of Health and Exercise Science; University of Oklahoma; 1401 Asp Avenue. Room 104 Norman Oklahoma USA 73019
| | - Travis W. Beck
- Biophysics Laboratory, Department of Health and Exercise Science; University of Oklahoma; 1401 Asp Avenue. Room 104 Norman Oklahoma USA 73019
| | - Nathan P. Wages
- Biophysics Laboratory, Department of Health and Exercise Science; University of Oklahoma; 1401 Asp Avenue. Room 104 Norman Oklahoma USA 73019
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