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Danielson TL, Gould LA, DeFreitas JM, MacLennan RJ, Ekstrand C, Borowsky R, Farthing JP, Andrushko JW. Activity in the pontine reticular nuclei scales with handgrip force in humans. J Neurophysiol 2024; 131:807-814. [PMID: 38505916 DOI: 10.1152/jn.00407.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2023] [Revised: 02/21/2024] [Accepted: 03/14/2024] [Indexed: 03/21/2024] Open
Abstract
The neural pathways that contribute to force production in humans are currently poorly understood, as the relative roles of the corticospinal tract and brainstem pathways, such as the reticulospinal tract (RST), vary substantially across species. Using functional magnetic resonance imaging (fMRI), we aimed to measure activation in the pontine reticular nuclei (PRN) during different submaximal handgrip contractions to determine the potential role of the PRN in force modulation. Thirteen neurologically intact participants (age: 28 ± 6 yr) performed unilateral handgrip contractions at 25%, 50%, 75% of maximum voluntary contraction during brain scans. We quantified the magnitude of PRN activation from the contralateral and ipsilateral sides during each of the three contraction intensities. A repeated-measures ANOVA demonstrated a significant main effect of force (P = 0.012, [Formula: see text] = 0.307) for PRN activation, independent of side (i.e., activation increased with force for both contralateral and ipsilateral nuclei). Further analyses of these data involved calculating the linear slope between the magnitude of activation and handgrip force for each region of interest (ROI) at the individual-level. One-sample t tests on the slopes revealed significant group-level scaling for the PRN bilaterally, but only the ipsilateral PRN remained significant after correcting for multiple comparisons. We show evidence of task-dependent activation in the PRN that was positively related to handgrip force. These data build on a growing body of literature that highlights the RST as a functionally relevant motor pathway for force modulation in humans.NEW & NOTEWORTHY In this study, we used a task-based functional magnetic resonance imaging (fMRI) paradigm to show that activity in the pontine reticular nuclei scales linearly with increasing force during a handgrip task. These findings directly support recently proposed hypotheses that the reticulospinal tract may play an important role in modulating force production in humans.
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Affiliation(s)
- Tyler L Danielson
- Applied Neuromuscular Physiology Laboratory, College of Education and Human Sciences, Oklahoma State University, Stillwater, Oklahoma, United States
| | - Layla A Gould
- Division of Neurosurgery, Department of Surgery, College of Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Jason M DeFreitas
- Department of Exercise Science, Falk College of Sport and Human Dynamics, Syracuse University, Syracuse, New York, United States
| | - Rob J MacLennan
- Department of Neurology, College of Medicine, University of Florida, Gainesville, Florida, United States
- Brain Rehabilitation Research Center, Malcom Randall VA Medical Center, Gainesville, Florida, United States
| | - Chelsea Ekstrand
- Department of Neuroscience, Faculty of Arts and Science, University of Lethbridge, Lethbridge, Alberta, Canada
| | - Ron Borowsky
- Department of Psychology and Health Studies, College of Arts and Science, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Jonathan P Farthing
- College of Kinesiology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Justin W Andrushko
- Department of Sport, Exercise and Rehabilitation, Faculty of Health and Life Sciences, Northumbria University, Newcastle upon Tyne, United Kingdom
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MacLennan RJ, Renshaw DW, Danielson TL, Gruber AD, Harper L, Reese SM, Mattern K, Winesett SP. Applications of cortico-cortical paired associative stimulation for age-related declines of hand function. J Physiol 2023; 601:5597-5599. [PMID: 37983194 DOI: 10.1113/jp285692] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2023] [Accepted: 11/01/2023] [Indexed: 11/22/2023] Open
Affiliation(s)
- Rob J MacLennan
- Department of Neurology, College of Medicine, University of Florida, Gainesville, Florida, USA
- Brain Rehabilitation Research Center, Malcom Randall VA Medical Center, Gainesville, Florida, USA
| | - Doug W Renshaw
- Department of Kinesiology, Sul Ross State University, Alpine, Texas, USA
| | - Tyler L Danielson
- School of Kinesiology, Applied Health, and Recreation, Oklahoma State University, Stillwater, Oklahoma, USA
| | - Anthony D Gruber
- Brain Rehabilitation Research Center, Malcom Randall VA Medical Center, Gainesville, Florida, USA
| | - Lacey Harper
- Department of Exercise Science and Sport Management, Kennesaw State University, Kennesaw, Georgia, USA
| | - Shawn M Reese
- School of Kinesiology, Applied Health, and Recreation, Oklahoma State University, Stillwater, Oklahoma, USA
| | - Kirk Mattern
- Department of Health Science, Stetson University, DeLand, Florida, USA
| | - Steven P Winesett
- Brain Rehabilitation Research Center, Malcom Randall VA Medical Center, Gainesville, Florida, USA
- Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida, USA
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Pagan JI, Harmon KK, Girts RM, MacLennan RJ, Beausejour JP, Hernandez-Sarabia JA, Coker NA, Carr JC, Ye X, DeFreitas JM, Stock MS. Sex-Specific Reliability of Lower-Limb Corticospinal Excitability and Silent Periods. J Strength Cond Res 2023; 37:1882-1887. [PMID: 37267320 DOI: 10.1519/jsc.0000000000004525] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
ABSTRACT Pagan, JI, Harmon, KK, Girts, RM, MacLennan, RJ, Beausejour, JP, Hernandez-Sarabia, JA, Coker, NA, Carr, JC, Ye, X, DeFreitas, JM, and Stock, MS. Sex-specific reliability of lower-limb corticospinal excitability and silent periods. J Strength Cond Res 37(9): 1882-1887, 2023-Transcranial magnetic stimulation (TMS) is a research tool that has potential to provide new insights into strength training-induced adaptations. However, using TMS to study the lower limbs is challenging, and sex-specific reliability has yet to be reported. We examined the reliability of corticospinal excitability and silent periods for the rectus femoris, vastus lateralis, and biceps femoris in both sexes. Thirteen males and 14 females reported to the laboratory twice. During both trials, a double cone coil was used to deliver 20 pulses to the rectus femoris hotspot with a stimulator output of 130% of active motor threshold. Motor-evoked potential peak-to-peak amplitude, which reflects corticospinal excitability, and silent period duration were quantified. Our results offer 4 novel findings. First, corticospinal excitability and silent period demonstrated higher reliability for the females. Second, regardless of sex and muscle, the silent period was more reliable than corticospinal excitability. Third, reliability was highest for our target muscle (rectus femoris), with lower reliability for the vastus lateralis and biceps femoris, suggesting that these methods cannot be used to study coactivation. Fourth, active motor threshold showed less variability than corticospinal excitability and silent period but increased at trial 2 in females. Many of the intraclass correlation coefficients were excellent (≥0.90), although we attribute this finding to variability between subjects. Reliability of lower-limb TMS measures may be sex, muscle, and variable dependent. Our findings suggest that both males and females should be included in lower-limb TMS research, although combining data between sexes should be approached cautiously.
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Affiliation(s)
- Jason I Pagan
- Neuromuscular Plasticity Laboratory, Institute of Exercise Physiology and Rehabilitation Science, University of Central Florida, Orlando, Florida
| | - Kylie K Harmon
- Department of Exercise Science, Syracuse University, Syracuse, New York
| | - Ryan M Girts
- Department of Natural and Health Sciences, Pfeiffer University, Misenheimer, North Carolina
| | - Rob J MacLennan
- Applied Neuromuscular Physiology Laboratory, Oklahoma State University, Stillwater, Oklahoma
| | - Jonathan P Beausejour
- Neuromuscular Plasticity Laboratory, Institute of Exercise Physiology and Rehabilitation Science, University of Central Florida, Orlando, Florida
| | - Jesus A Hernandez-Sarabia
- Posture and Gait Neuromechanics Laboratory, California State University, Bakersfield, Bakersfield, California
| | - Nicholas A Coker
- Department of Exercise Science and Athletic Training, Springfield College, Springfield, Massachusetts
| | - Joshua C Carr
- Department of Kinesiology, Texas Christian University, Fort Worth, Texas
- Department of Medical Education, Texas Christian University School of Medicine, Fort Worth, Texas; and
| | - Xin Ye
- Doctor of Physical Therapy Program, Department of Rehabilitation Sciences, University of Hartford, West Hartford, Connecticut
| | - Jason M DeFreitas
- Applied Neuromuscular Physiology Laboratory, Oklahoma State University, Stillwater, Oklahoma
| | - Matt S Stock
- Neuromuscular Plasticity Laboratory, Institute of Exercise Physiology and Rehabilitation Science, University of Central Florida, Orlando, Florida
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MacLennan DL, Plahovinsak JL, MacLennan RJ, Jones CT. Clinical Trial Site Perspectives and Practices on Study Participant Diversity and Inclusion. Clin Pharmacol Ther 2023; 113:670-679. [PMID: 36495475 DOI: 10.1002/cpt.2817] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2022] [Accepted: 12/08/2022] [Indexed: 12/14/2022]
Abstract
Clinical trial participant populations fail to adequately represent target populations that drugs are intended to serve. Improving racial and ethnic diversity of clinical trial participants is essential for generalizable, quality clinical research results and ensuring social and medical equity. Site-level clinical research professionals (CRPs) have unique insights on diversity improvement strategies for clinical trial enrollment. A survey was distributed to current CRPs working at clinical research sites in the United States to describe current practices and perceptions of the impact these practices have on participant diversity. Subsequently, descriptive quantitative analysis and inductive content analysis were performed. For the practices surveyed, there are discrepancies between frequency of use and perceived impact on diversity enrollment. Common current practices include phone-based or telemedicine study visits, electronic/digital data collection, and participant compensation. However, we report travel reimbursement and services, translated documents and translator services, and adequate participant compensation as most impactful on diverse enrollment. A multistakeholder approach is necessary to enhance diversity and inclusion (D&I) of study participants. Besides large-scale solutions such as countering community distrust, actionable steps are needed by sponsors and study sites to improve D&I of trial participants. Study leadership at the sponsor, contract research organization (CRO), and site-level should create diversity plans prior to study start, and CRO and sponsor budgets should consider D&I strategies during study planning. Planning should incorporate strategies to improve D&I including adequate participant compensation, translated documents and translator services, and travel reimbursements.
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Affiliation(s)
- Demi L MacLennan
- College of Pharmacy, The Ohio State University, Columbus, Ohio, USA
| | | | - Rob J MacLennan
- Applied Neuromuscular Physiology Laboratory, Oklahoma State University, Stillwater, Oklahoma, USA
| | - Carolynn T Jones
- College of Nursing and Center for Clinical Translational Research, The Ohio State University, Columbus, Ohio, USA
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MacLennan RJ, Hernandez-Sarabia JA, Pagan JI, Girts RM, Harmon KK, Stute K, Coker NA, Carr JC, Ye X, Stock MS, DeFreitas JM. Sensitivity Of Fnirs Brain Imaging To Determine Hemispheric Laterality During Lower-body Motor Tasks. Med Sci Sports Exerc 2022. [DOI: 10.1249/01.mss.0000882148.77052.04] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Chavez L, Barrera-Curiel A, Shields J, Hernandez-Sarabia JA, Danielson T, MacLennan RJ, DeFreitas JM. Is There A Relationship Between Antagonist Coactivation And Reaction Time During Dual-tasks? Med Sci Sports Exerc 2022. [DOI: 10.1249/01.mss.0000882156.47410.1b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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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] [What about the content of this article? (0)] [Affiliation(s)] [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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Logeson ZS, MacLennan RJ, Abad GKB, Methven JM, Gradl MR, Pinto MD, Pinto RS, Stock MS. The impact of skeletal muscle disuse on distinct echo intensity bands: A retrospective analysis. PLoS One 2022; 17:e0262553. [PMID: 35015790 PMCID: PMC8752001 DOI: 10.1371/journal.pone.0262553] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2021] [Accepted: 12/28/2021] [Indexed: 11/18/2022] Open
Abstract
Echo intensity (EI) is a novel tool for assessing muscle quality. EI has traditionally been reported as the mean of the pixel histogram, with 0 and 255 arbitrary units (A.U.) representing excellent and poor muscle quality, respectively. Recent work conducted in youth and younger and older adults suggested that analyzing specific EI bands, rather than the mean, may provide unique insights into the effectiveness of exercise and rehabilitation interventions. As our previous work showed deterioration of muscle quality after knee joint immobilization, we sought to investigate whether the increase in EI following disuse was limited to specific EI bands. Thirteen females (age = 21 yrs) underwent two weeks of left knee immobilization and ambulated via crutches. B-mode ultrasonography was utilized to obtain images of the immobilized vastus lateralis. The percentage of the total number of pixels within bands of 0–50, 51–100, 101–150, 151–200, and 201–255 A.U. was examined before and after immobilization. We also sought to determine if further subdividing the histogram into 25 A.U. bands (i.e., 0–25, 26–50, etc.) would be a more sensitive methodological approach. Immobilization resulted in a decrease in the percentage of pixels within the 0–50 A.U. band (-3.11 ± 3.98%), but an increase in the 101–150 A.U. (2.94 ± 2.64%) and 151–200 A.U. (0.93 ± 1.42%) bands. Analyses of variance on the change scores indicated that these differences were large and significant (%EI0-50 vs. %EI101-150: p < .001, d = 1.243); %EI0-50 vs. %EI151-200: p = .043, d = 0.831). The effect size for the %EI51-100 versus %EI101-150 comparison was medium/large (d = 0.762), but not statistically significant (p = .085). Further analysis of the 25 A.U. bands indicated that the percentage of pixels within the 25–50 A.U. band decreased (-2.97 ± 3.64%), whereas the 101–125 (1.62 ± 1.47%) and 126–150 A.U. (1.18 ± 1.07%) bands increased. Comparison of the 50 A.U. and 25 A.U. band methods found that 25 A.U. bands offer little additional insight. Though studies are needed to ascertain the factors that may influence specific bands, changes in EI during muscle disuse are not homogeneous across the pixel histogram. We encourage investigators to think critically about the robustness of data obtained from EI histograms, rather than simply reporting the EImean value, in muscle quality research.
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Affiliation(s)
- Zachary S. Logeson
- Neuromuscular Plasticity Laboratory, Institute of Exercise Physiology and Rehabilitation Science, University of Central Florida, Orlando, Florida, United States of America
| | - Rob J. MacLennan
- Applied Neuromuscular Physiology Laboratory, Oklahoma State University, Stillwater, Oklahoma, United States of America
| | - Gerard-Kyle B. Abad
- Neuromuscular Plasticity Laboratory, Institute of Exercise Physiology and Rehabilitation Science, University of Central Florida, Orlando, Florida, United States of America
| | - Johnathon M. Methven
- Neuromuscular Plasticity Laboratory, Institute of Exercise Physiology and Rehabilitation Science, University of Central Florida, Orlando, Florida, United States of America
| | - Molly R. Gradl
- Neuromuscular Plasticity Laboratory, Institute of Exercise Physiology and Rehabilitation Science, University of Central Florida, Orlando, Florida, United States of America
| | - Matheus D. Pinto
- Centre for Exercise and Sport Science Research (CESSR), School of Medical and Health Sciences, Edith Cowan University, Joondalup, Australia
| | - Ronei S. Pinto
- Exercise Research Laboratory, Physical Education, Physiotherapy and Dance School, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil
| | - Matt S. Stock
- Neuromuscular Plasticity Laboratory, Institute of Exercise Physiology and Rehabilitation Science, University of Central Florida, Orlando, Florida, United States of America
- * E-mail:
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Girts RM, MacLennan RJ, Harmon KK, Stock MS. Is skeletal muscle echo intensity more indicative of voluntary or involuntary strength in young women? Transl Sports Med 2021. [DOI: 10.1002/tsm2.234] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- Ryan M. Girts
- Neuromuscular Plasticity Laboratory School of Kinesiology and Physical Therapy University of Central Florida Orlando FL USA
- Institute of Exercise Physiology and Rehabilitation Science University of Central Florida Orlando FL USA
| | - Rob J. MacLennan
- Applied Neuromuscular Physiology Laboratory Oklahoma State University Stillwater OK USA
| | - Kylie K. Harmon
- Neuromuscular Plasticity Laboratory School of Kinesiology and Physical Therapy University of Central Florida Orlando FL USA
- Institute of Exercise Physiology and Rehabilitation Science University of Central Florida Orlando FL USA
| | - Matt S. Stock
- Neuromuscular Plasticity Laboratory School of Kinesiology and Physical Therapy University of Central Florida Orlando FL USA
- Institute of Exercise Physiology and Rehabilitation Science University of Central Florida Orlando FL USA
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MacLennan RJ, Ogilvie D, McDorman J, Vargas E, Grusky AR, Kim Y, Garcia JM, Stock MS. The time course of neuromuscular impairment during short-term disuse in young women. Physiol Rep 2021; 9:e14677. [PMID: 33426809 PMCID: PMC7797948 DOI: 10.14814/phy2.14677] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2020] [Accepted: 11/14/2020] [Indexed: 12/27/2022] Open
Abstract
Skeletal muscle disuse results in rapid functional declines. Previous studies have typically been at least 1 week in duration and focused on the responsiveness of men. Herein, we report the timeline of initial impairments in strength, voluntary activation (VA), and motor unit control during 2 weeks of knee joint immobilization. Thirteen women (mean age =21 years) underwent 2 weeks of left knee joint immobilization via ambulation on crutches and use of a brace. Participants visited the laboratory for testing on seven occasions (two familiarization visits, pretest, 48 and 72 h, 1 and 2 weeks). Knee extensor isometric and concentric isokinetic strength at two velocities (180 and 360 degrees⋅s-1 ), VA, and submaximal vastus lateralis motor unit activity were evaluated. Moderate-to-large decreases in isometric and concentric strength at 180 degrees⋅s-1 and VA were observed within 48 hours. Isometric strength continued to decline beyond 72 h, whereas other variables plateaued. The B-term of the motor unit mean firing rate versus action potential amplitude relationship demonstrated a moderate increase 1 week into immobilization, suggesting that greater firing rates were necessary to maintain pretest torque levels. Concentric strength at a velocity of 360 degrees s-1 was not affected. Decreases in knee extensor strength occur within a matter of days after immobilization, although the time course and magnitude vary among assessment methods. These changes are mediated by the nervous system's capacity to activate skeletal muscle. Clinically appropriate interventions which target nervous system plasticity should be implemented early to minimize the rapid functional impairments associated with disuse.
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Affiliation(s)
- Rob J MacLennan
- Applied Neuromuscular Physiology Laboratory, Oklahoma State University, Stillwater, OK, USA
| | - David Ogilvie
- School of Kinesiology & Physical Therapy, University of Central Florida, Orlando, FL, USA.,Neuromuscular Plasticity Laboratory, Institute of Exercise Physiology and Rehabilitation Science, University of Central Florida, Orlando, FL, USA
| | - John McDorman
- School of Kinesiology & Physical Therapy, University of Central Florida, Orlando, FL, USA.,Neuromuscular Plasticity Laboratory, Institute of Exercise Physiology and Rehabilitation Science, University of Central Florida, Orlando, FL, USA
| | - Ernest Vargas
- School of Kinesiology & Physical Therapy, University of Central Florida, Orlando, FL, USA.,Neuromuscular Plasticity Laboratory, Institute of Exercise Physiology and Rehabilitation Science, University of Central Florida, Orlando, FL, USA
| | - Arielle R Grusky
- School of Kinesiology & Physical Therapy, University of Central Florida, Orlando, FL, USA.,Neuromuscular Plasticity Laboratory, Institute of Exercise Physiology and Rehabilitation Science, University of Central Florida, Orlando, FL, USA
| | - Youngdeok Kim
- Department of Kinesiology and Health Sciences, Virginia Commonwealth University, Richmond, VA, USA
| | - Jeanette M Garcia
- Department of Health Sciences, University of Central Florida, Orlando, FL, USA
| | - Matt S Stock
- School of Kinesiology & Physical Therapy, University of Central Florida, Orlando, FL, USA.,Neuromuscular Plasticity Laboratory, Institute of Exercise Physiology and Rehabilitation Science, University of Central Florida, Orlando, FL, USA
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Girts RM, Mota JA, Harmon KK, MacLennan RJ, Stock MS. Vastus Lateralis Motor Unit Recruitment Thresholds Are Compressed towards Lower Forces in Older Men. J Frailty Aging 2020; 9:191-196. [PMID: 32996555 DOI: 10.14283/jfa.2020.19] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
BACKGROUND Aging results in adaptations which may affect the control of motor units. OBJECTIVE We sought to determine if younger and older men recruit motor units at similar force levels. DESIGN Cross-sectional, between-subjects design. SETTING Controlled laboratory setting. PARTICIPANTS Twelve younger (age = 25 ± 3 years) and twelve older (age = 75 ± 8 years) men. MEASUREMENTS Participants performed isometric contractions of the dominant knee extensors at a force level corresponding to 50% maximal voluntary contraction (MVC). Bipolar surface electromyographic (EMG) signals were detected from the vastus lateralis. A surface EMG signal decomposition algorithm was used to quantify the recruitment threshold of each motor unit, which was defined as the force level corresponding to the first firing. Recruitment thresholds were expressed in both relative (% MVC) and absolute (N) terms. To further understand age-related differences in motor unit control, we examined the mean firing rate versus recruitment threshold relationship at steady force. RESULTS MVC force was greater in younger men (p = 0.010, d = 1.15). Older men had lower median recruitment thresholds in both absolute (p = 0.005, d = 1.29) and relative (p = 0.001, d = 1.53) terms. The absolute recruitment threshold range was larger for younger men (p = 0.020; d = 1.02), though a smaller difference was noted in relative terms (p = 0.235, d = 0.50). These findings were complimented by a generally flatter slope (p = 0.070; d = 0.78) and lower y-intercept (p = 0.009; d = 1.17) of the mean firing rate versus recruitment threshold relationship in older men. CONCLUSION Older men tend to recruit more motor units at lower force levels. We speculate that recruitment threshold compression may be a neural adaptation serving to compensate for lower motor unit firing rates and/or denervation and subsequent re-innervation in aged muscle.
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Affiliation(s)
- R M Girts
- Matt S. Stock, Ph.D., School of Kinesiology and Physical Therapy, University of Central Florida, 12805 Pegasus Drive, HPA 1 - Room 258, Orlando, FL 32816-2205, Phone: (407) 823-0364, Fax: (407) 823-2596, E-mail:
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MacLennan RJ, Harmon KK, Shields JE, Andrushko JW, Girts RM, Danielson TL. Aspects of cortical area responsibilities while learning a visually cued spatiotemporal motor task. J Physiol 2020; 599:13-14. [PMID: 32965704 DOI: 10.1113/jp280647] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2020] [Accepted: 09/22/2020] [Indexed: 11/08/2022] Open
Affiliation(s)
- Rob J MacLennan
- Applied Neuromuscular Physiology Laboratory, Oklahoma State University, Stillwater, OK, USA
| | - Kylie K Harmon
- Neuromuscular Plasticity Laboratory, School of Kinesiology and Physical Therapy, University of Central Florida, Orlando, FL, USA
| | - JoCarol E Shields
- Applied Neuromuscular Physiology Laboratory, Oklahoma State University, Stillwater, OK, USA
| | - Justin W Andrushko
- College of Kinesiology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
| | - Ryan M Girts
- Neuromuscular Plasticity Laboratory, School of Kinesiology and Physical Therapy, University of Central Florida, Orlando, FL, USA
| | - Tyler L Danielson
- Applied Neuromuscular Physiology Laboratory, Oklahoma State University, Stillwater, OK, USA
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MacLennan RJ, Swafford AP, Kwon DP, DeFreitas JM, Stock MS. Do Decreases In Voluntary Activation Account For Fatigability Differently In Males And Females? Med Sci Sports Exerc 2020. [DOI: 10.1249/01.mss.0000685684.83393.3c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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MacLennan RJ, Sahebi M, Becker N, Davis E, Garcia JM, Stock MS. Declines in skeletal muscle quality vs. size following two weeks of knee joint immobilization. PeerJ 2020; 8:e8224. [PMID: 31976172 PMCID: PMC6964688 DOI: 10.7717/peerj.8224] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2019] [Accepted: 11/15/2019] [Indexed: 12/27/2022] Open
Abstract
Background Disuse of a muscle group, which occurs during bedrest, spaceflight, and limb immobilization, results in atrophy. It is unclear, however, if the magnitude of decline in skeletal muscle quality is similar to that for muscle size. The purpose of this study was to examine the effects of two weeks of knee joint immobilization on vastus lateralis and rectus femoris echo intensity and cross-sectional area. Methods Thirteen females (mean ± SD age = 21 ± 2 years) underwent two weeks of left knee joint immobilization via ambulating on crutches and use of a brace. B-mode ultrasonography was utilized to obtain transverse plane images of the immobilized and control vastus lateralis and rectus femoris at pretest and following immobilization. Effect size statistics and two-way repeated measures analyses of variance were used to interpret the data. Results No meaningful changes were demonstrated for the control limb and the rectus femoris of the immobilized limb. Analyses showed a large increase in vastus lateralis echo intensity (i.e., decreased muscle quality) for the immobilized limb (p = .006, Cohen’s d = .918). For vastus lateralis cross-sectional area, no time × limb interaction was observed (p = .103), but the effect size was moderate (d = .570). There was a significant association between the increase in vastus lateralis echo intensity and the decrease in cross-sectional area (r = − .649, p = .016). Conclusion In female participants, two weeks of knee joint immobilization resulted in greater deterioration of muscle quality than muscle size. Echo intensity appears to be an attractive clinical tool for monitoring muscle quality during disuse.
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Affiliation(s)
- Rob J MacLennan
- School of Kinesiology and Physical Therapy, University of Central Florida, Orlando, FL, United States of America
| | - Michael Sahebi
- School of Kinesiology and Physical Therapy, University of Central Florida, Orlando, FL, United States of America
| | - Nathan Becker
- School of Kinesiology and Physical Therapy, University of Central Florida, Orlando, FL, United States of America
| | - Ethan Davis
- School of Kinesiology and Physical Therapy, University of Central Florida, Orlando, FL, United States of America
| | - Jeanette M Garcia
- Department of Health Sciences, University of Central Florida, Orlando, FL, United States of America
| | - Matt S Stock
- School of Kinesiology and Physical Therapy, University of Central Florida, Orlando, FL, United States of America
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15
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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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16
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Swafford AP, Kwon DP, MacLennan RJ, Fukuda DH, Stout JR, Stock MS. No acute effects of placebo or open-label placebo treatments on strength, voluntary activation, and neuromuscular fatigue. Eur J Appl Physiol 2019; 119:2327-2338. [PMID: 31468171 DOI: 10.1007/s00421-019-04219-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2019] [Accepted: 08/25/2019] [Indexed: 12/17/2022]
Abstract
PURPOSE Recent evidence suggests that deception may not be necessary for placebos to improve clinical outcomes. We tested the hypothesis that placebo and open-label placebo (OLP) treatments would acutely improve strength and voluntary activation, as well as minimize neuromuscular fatigue, in untrained participants. METHODS Twenty-one males (n = 11) and females (n = 10) visited the laboratory on three occasions (placebo, OLP, control) to receive each treatment in a randomized, counter-balanced manner. Trials involved a pretest, a 15-min intervention, and posttests. For the placebo trial, participants were informed that they would be ingesting a capsule that would improve their performance and make them feel more energetic. For the OLP intervention, participants were told that the capsules would have no effects. In "Experiment #1", knee extensor maximal voluntary contraction (MVC) peak torque and percent voluntary activation were evaluated. In "Experiment #2", participants performed 20 consecutive MVCs while surface electromyographic signals were detected from the vastus lateralis. Subjective assessments of energy and perceived exertion were examined. RESULTS The interventions had no effect on strength or voluntary activation, but energy levels increased following treatments (p = 0.016, η2 = 0.257). Neither treatment influenced neuromuscular fatigue. Though some variables showed moderate-to-large effect sizes, these results were consistent for individuals with lower voluntary activation. CONCLUSION Placebo and OLP treatments had minimal influence on strength, voluntary activation, and fatigue resistance. As these findings differ from recent reports, we speculate that placebos and OLPs are more likely to enhance muscle function in patient populations seeking medical care.
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Affiliation(s)
- Alina P Swafford
- School of Kinesiology and Physical Therapy, College of Health Professions and Sciences, University of Central Florida, 12805 Pegasus Drive, HPA 1, Room 258, Orlando, FL, 32816-2205, USA
| | - Dennis P Kwon
- School of Kinesiology and Physical Therapy, College of Health Professions and Sciences, University of Central Florida, 12805 Pegasus Drive, HPA 1, Room 258, Orlando, FL, 32816-2205, USA
| | - Rob J MacLennan
- School of Kinesiology and Physical Therapy, College of Health Professions and Sciences, University of Central Florida, 12805 Pegasus Drive, HPA 1, Room 258, Orlando, FL, 32816-2205, USA
| | - David H Fukuda
- School of Kinesiology and Physical Therapy, College of Health Professions and Sciences, University of Central Florida, 12805 Pegasus Drive, HPA 1, Room 258, Orlando, FL, 32816-2205, USA
| | - Jeffrey R Stout
- School of Kinesiology and Physical Therapy, College of Health Professions and Sciences, University of Central Florida, 12805 Pegasus Drive, HPA 1, Room 258, Orlando, FL, 32816-2205, USA
| | - Matt S Stock
- School of Kinesiology and Physical Therapy, College of Health Professions and Sciences, University of Central Florida, 12805 Pegasus Drive, HPA 1, Room 258, Orlando, FL, 32816-2205, USA.
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MacLennan RJ, Ogilvie D, McDorman J, Vargas E, Becker N, Davis E, Sahebi M, Stock MS. The Motor Unit Mean Firing Rate versus Recruitment Threshold Relationship is Unaffected by Short-Term Disuse. Med Sci Sports Exerc 2019. [DOI: 10.1249/01.mss.0000561537.15094.0a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Girts R, Mota JA, Harmon KK, MacLennan RJ, Stock MS. Vastus Lateralis Motor Unit Recruitment Thresholds in Younger Versus Older Men. Med Sci Sports Exerc 2019. [DOI: 10.1249/01.mss.0000561541.81921.2f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Sahebi M, MacLennan RJ, Becker N, Davis E, Ogilvie D, McDorman J, Vargas E, Stock MS. Vastus Lateralis Muscle Quality Deteriorates More So Than Muscle Size During Knee Joint Immoblization. Med Sci Sports Exerc 2019. [DOI: 10.1249/01.mss.0000563203.65214.0a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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