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Lecce E, Conti A, Nuccio S, Felici F, Bazzucchi I. Characterising sex-related differences in lower- and higher-threshold motor unit behaviour through high-density surface electromyography. Exp Physiol 2024; 109:1317-1329. [PMID: 38888901 PMCID: PMC11291872 DOI: 10.1113/ep091823] [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: 02/14/2024] [Accepted: 05/28/2024] [Indexed: 06/20/2024]
Abstract
Emerging questions in neuromuscular physiology revolve around whether males and females share similar neural control in diverse tasks across a broad range of intensities. In order to explore these features, high-density electromyography was used to record the myoelectrical activity of biceps brachii during trapezoidal isometric contractions at 35% and 70% of maximal voluntary force (MVF) on 11 male and 13 female participants. Identified motor units were then classified as lower-threshold (recruited at ≤30%MVF) and higher-threshold (recruited at >30%MVF). The discharge rate, interspike interval variability, recruitment and derecruitment thresholds, and estimates of neural drive to motor neurons were assessed. Female lower-threshold motor units showed higher neural drive (P < 0.001), accompanied by higher discharge rate at recruitment (P = 0.006), plateau (P = 0.001) and derecruitment (P = 0.001). On the other hand, male higher-threshold motor units showed greater neural drive (P = 0.04), accompanied by higher discharge rate at recruitment (P = 0.005), plateau (P = 0.04) and derecruitment (P = 0.01). Motor unit discharge rate normalised by the recruitment threshold was significantly higher in female lower-threshold motor units (P < 0.001), while no differences were observed in higher-threshold motor units. Recruitment and derecruitment thresholds are higher in males across all intensities (P < 0.01). However, males and females have similar activation and deactivation strategies, as evidenced by similar recruitment-to-derecruitment ratios (P > 0.05). This study encompasses a broad intensity range to analyse motor unit sex-related differences, highlighting higher neural drive and discharge rates in female lower-threshold motor units, elevated recruitment and derecruitment thresholds in males, and convergences in activation and deactivation strategies. HIGHLIGHTS: What is the central question of the study? Do male and female motor units behave similarly in low- and high-intensity contractions? What is the main finding and its importance? Female motor units show higher discharge rates in low-intensity tasks and lower discharge rates in high-intensity tasks, with no differences in recruitment behaviour. A broader inter-spike interval variability was also observed in females. These findings underline that there are sex-specific differences concern the firing strategies based on task intensity.
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Affiliation(s)
- Edoardo Lecce
- Department of Movement, Human and Health Sciences, Laboratory of Exercise PhysiologyUniversity of Rome ‘Foro Italico’RomeItaly
| | - Alessandra Conti
- Department of Movement, Human and Health Sciences, Laboratory of Exercise PhysiologyUniversity of Rome ‘Foro Italico’RomeItaly
| | - Stefano Nuccio
- Department of Movement, Human and Health Sciences, Laboratory of Exercise PhysiologyUniversity of Rome ‘Foro Italico’RomeItaly
| | - Francesco Felici
- Department of Movement, Human and Health Sciences, Laboratory of Exercise PhysiologyUniversity of Rome ‘Foro Italico’RomeItaly
| | - Ilenia Bazzucchi
- Department of Movement, Human and Health Sciences, Laboratory of Exercise PhysiologyUniversity of Rome ‘Foro Italico’RomeItaly
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Nishikawa Y, Watanabe K, Holobar A, Kitamura R, Maeda N, Hyngstrom AS. Sex differences in laterality of motor unit firing behavior of the first dorsal interosseous muscle in strength-matched healthy young males and females. Eur J Appl Physiol 2024; 124:1979-1990. [PMID: 38366213 PMCID: PMC11199256 DOI: 10.1007/s00421-024-05420-7] [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: 04/28/2023] [Accepted: 01/11/2024] [Indexed: 02/18/2024]
Abstract
PURPOSE The purpose of this study was to compare laterality in motor unit firing behavior between females and males. METHODS Twenty-seven subjects (14 females) were recruited for this study. The participants performed ramp up and hold isometric index finger abduction at 10, 30, and 60% of their maximum voluntary contraction (MVC). High-density surface electromyography (HD-sEMG) signals were recorded in the first dorsal interosseous (FDI) muscle and decomposed into individual motor unit (MU) firing behavior using a convolution blind source separation method. RESULTS In total, 769 MUs were detected (females, n = 318 and males, n = 451). Females had a significantly higher discharge rate than males at each relative torque level (10%: male dominant hand, 13.4 ± 2.7 pps vs. female dominant hand, 16.3 ± 3.4 pps; 30%: male dominant hand, 16.1 ± 3.9 pps vs. female dominant hand, 20.0 ± 5.0 pps; and 60%: male dominant hand, 19.3 ± 3.8 vs. female dominant hand, 25.3 ± 4.8 pps; p < 0.0001). The recruitment threshold was also significantly higher in females than in males at 30 and 60% MVC. Furthermore, males exhibited asymmetrical discharge rates at 30 and 60% MVC and recruitment thresholds at 30 and 60% MVC, whereas no asymmetry was observed in females. CONCLUSION In the FDI muscle, compared to males, females exhibited different neuromuscular strategies with higher discharge rates and recruitment thresholds and no asymmetrical MU firing behavior. Notably, the findings that sex differences in neuromuscular activity also occur in healthy individuals provide important information for understanding the pathogenesis of various diseases.
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Affiliation(s)
- Yuichi Nishikawa
- Faculty of Frontier Engineering, Institute of Science & Engineering, Kanazawa University, Kakuma-machi, Kanazawa, 920-1192, Japan.
| | - Kohei Watanabe
- Laboratory of Neuromuscular Biomechanics, School of Health and Sport Sciences, Chukyo University, Nagoya, Japan
| | - Aleš Holobar
- Faculty of Electrical Engineering and Computer Science, University of Maribor, Maribor, Slovenia
| | - Ryoka Kitamura
- Graduate School of Frontier Engineering, Kanazawa University, Kanazawa, Japan
| | - Noriaki Maeda
- Division of Sports Rehabilitation, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan
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Marsala MJ, Gabriel DA, Greig Inglis J, Christie AD. How many motor units is enough? An assessment of the influence of the number of motor units on firing rate calculations. J Electromyogr Kinesiol 2024; 75:102872. [PMID: 38458102 DOI: 10.1016/j.jelekin.2024.102872] [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: 09/15/2023] [Revised: 02/25/2024] [Accepted: 03/02/2024] [Indexed: 03/10/2024] Open
Abstract
The number of motor units included in calculations of mean firing rates varies widely in the literature. It is unknown how the number of decomposed motor units included in the calculation of firing rate per participant compares to the total number of active motor units in the muscle, and if this is different for males and females. Bootstrapped distributions and confidence intervals (CI) of mean motor unit firing rates decomposed from the tibialis anterior were used to represent the total number of active motor units for individual participants in trials from 20 to 100 % of maximal voluntary contraction. Bootstrapped distributions of mean firing rates were constructed using different numbers of motor units, from one to the maximum number for each participant, and compared to the CIs. A probability measure for each number of motor units involved in firing rate was calculated and then averaged across all individuals. Motor unit numbers required for similar levels of probability increased as contraction intensity increased (p < 0.001). Increased levels of probability also required higher numbers of motor units (p < 0.001). There was no effect of sex (p ≥ 0.97) for any comparison. This methodology should be repeated in other muscles, and aged populations.
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Affiliation(s)
- Michael J Marsala
- School of Kinesiology, University of Western Ontario, 1151 Richmond St., London, Ontario N6A 3K7, Canada
| | - David A Gabriel
- Department of Kinesiology, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, ON L2S 3A1, Canada
| | - J Greig Inglis
- Department of Kinesiology, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, ON L2S 3A1, Canada
| | - Anita D Christie
- School of Kinesiology, University of Western Ontario, 1151 Richmond St., London, Ontario N6A 3K7, Canada.
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Giuriato G, Romanelli MG, Bartolini D, Vernillo G, Pedrinolla A, Moro T, Franchi M, Locatelli E, Andani ME, Laginestra FG, Barbi C, Aloisi GF, Cavedon V, Milanese C, Orlandi E, De Simone T, Fochi S, Patuzzo C, Malerba G, Fabene P, Donadelli M, Stabile AM, Pistilli A, Rende M, Galli F, Schena F, Venturelli M. Sex differences in neuromuscular and biological determinants of isometric maximal force. Acta Physiol (Oxf) 2024; 240:e14118. [PMID: 38385696 DOI: 10.1111/apha.14118] [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: 11/21/2023] [Revised: 01/29/2024] [Accepted: 02/09/2024] [Indexed: 02/23/2024]
Abstract
AIM Force expression is characterized by an interplay of biological and molecular determinants that are expected to differentiate males and females in terms of maximal performance. These include muscle characteristics (muscle size, fiber type, contractility), neuromuscular regulation (central and peripheral factors of force expression), and individual genetic factors (miRNAs and gene/protein expression). This research aims to comprehensively assess these physiological variables and their role as determinants of maximal force difference between sexes. METHODS Experimental evaluations include neuromuscular components of isometric contraction, intrinsic muscle characteristics (proteins and fiber type), and some biomarkers associated with muscle function (circulating miRNAs and gut microbiome) in 12 young and healthy males and 12 females. RESULTS Male strength superiority appears to stem primarily from muscle size while muscle fiber-type distribution plays a crucial role in contractile properties. Moderate-to-strong pooled correlations between these muscle parameters were established with specific circulating miRNAs, as well as muscle and plasma proteins. CONCLUSION Muscle size is crucial in explaining the differences in maximal voluntary isometric force generation between males and females with similar fiber type distribution. Potential physiological mechanisms are seen from associations between maximal force, skeletal muscle contractile properties, and biological markers.
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Affiliation(s)
- Gaia Giuriato
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
- Surgical, Medical and Dental Department of Morphological Sciences Related to Transplant, Oncology and Regenerative Medicine, University of Modena and Reggio Emilia, Modena, Italy
| | - Maria Grazia Romanelli
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
| | - Desirée Bartolini
- Department of Pharmaceutical Sciences, University of Perugia, Perugia, Italy
| | - Gianluca Vernillo
- Department of Biomedical Sciences for Health, Università degli Studi di Milano, Milan, Italy
- Department of Social Sciences, University of Alberta - Augustana Campus, Camrose, Alberta, Canada
| | - Anna Pedrinolla
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
- Department of Cellular, Computational and Integrative Biology (CIBIO), University of Trento, Trento, Italy
| | - Tatiana Moro
- Department of Biomedical Sciences, University of Padova, Padova, Italy
| | - Martino Franchi
- Department of Biomedical Sciences, University of Padova, Padova, Italy
| | - Elena Locatelli
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
| | - Mehran Emadi Andani
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
| | - Fabio Giuseppe Laginestra
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
- Department of Anesthesiology, University of Utah, Utah, USA
| | - Chiara Barbi
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
| | - Gloria Fiorini Aloisi
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
| | - Valentina Cavedon
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
| | - Chiara Milanese
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
| | - Elisa Orlandi
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
| | - Tonia De Simone
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
| | - Stefania Fochi
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
| | - Cristina Patuzzo
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
| | - Giovanni Malerba
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
| | - Paolo Fabene
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
| | - Massimo Donadelli
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
| | - Anna Maria Stabile
- Department of Medicine and Surgery, Section of Human Anatomy, Clinical and Forensic, School of Medicine, University of Perugia, Perugia, Italy
| | - Alessandra Pistilli
- Department of Medicine and Surgery, Section of Human Anatomy, Clinical and Forensic, School of Medicine, University of Perugia, Perugia, Italy
| | - Mario Rende
- Department of Medicine and Surgery, Section of Human Anatomy, Clinical and Forensic, School of Medicine, University of Perugia, Perugia, Italy
| | - Francesco Galli
- Department of Pharmaceutical Sciences, University of Perugia, Perugia, Italy
| | - Federico Schena
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
| | - Massimo Venturelli
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
- Department of Internal Medicine, University of Utah, Utah, USA
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Marsala MJ, Christie AD. Neuromuscular behaviour in the first dorsal interosseus following mental fatigue. Exp Physiol 2024; 109:416-426. [PMID: 38130030 PMCID: PMC10988746 DOI: 10.1113/ep091349] [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: 06/13/2023] [Accepted: 11/28/2023] [Indexed: 12/23/2023]
Abstract
We examined sex-specific changes to neuromuscular function in response to mental fatigue. Twenty-five young, healthy adults (13 F, 12 M) performed a mentally fatiguing task and control condition for 30 min on two separate days. Neuromuscular function was assessed in the first dorsal interosseous before and after each condition. Reaction time decreased after the mentally fatiguing task (P < 0.001, η2 = 0.47). Males and females reported higher levels of subjective fatigue after the mentally fatiguing task (P < 0.02, η2 = 0.07). Motor unit firing rate increased over time at 10% maximal voluntary contraction (MVC; P < 0.04, η2 = 0.16), and decreased over time at 50% MVC (P < 0.01, η2 = 0.14); however, this was not unique to either sex. During a variable force contraction, error decreased in females over time and increased in males (P < 0.05, η2 = 0.13), although changes were not unique to mental fatigue. Physiological function of the neuromuscular system was not specifically affected by mental fatigue in males or females.
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Affiliation(s)
- Michael J. Marsala
- School of Kinesiology, Faculty of Health SciencesThe University of Western OntarioOntarioCanada
| | - Anita D. Christie
- School of Kinesiology, Faculty of Health SciencesThe University of Western OntarioOntarioCanada
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Carr JC, King AC. Sex differences in the fractal dynamics of force control during maximal handgrip. Neurosci Lett 2024; 820:137588. [PMID: 38086520 DOI: 10.1016/j.neulet.2023.137588] [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: 07/01/2023] [Revised: 12/04/2023] [Accepted: 12/06/2023] [Indexed: 12/17/2023]
Abstract
This work examines the temporal structure of force fluctuations during maximal handgrip with detrended fluctuation analysis (DFA α). Here, we assess the influence of fatigue and sex on force complexity during unimanual handgrip for the fatigued and the contralateral, non-fatigued hand. Participants randomly completed experimental sessions requiring fatiguing handgrip contractions or control measurements only. Maximal unimanual forces of both hands were measured before and after the fatigue trial or a time-matched control visit. DFA revealed substantially lower alpha values for females (PRE = 1.15, POST = 1.25) compared to males (PRE = 1.30, POST = 1.33) regardless of fatigue (p < 0.01, d = 0.738) for the dominant hand with a similar pattern observed for the contralateral, non-fatigued hand (p = 0.045, d = 0.561). Females also showed greater alpha changes (Δ = 0.09) versus males (Δ = 0.01) following fatigue (p = 0.028, ηp2 = 0.151). The data provide evidence of reduced force complexity during successive maximal handgrip contractions for females, but not males. Our findings highlight task-specific factors involving force control and demonstrate the utility of complexity analyses to provide insights regarding the influence of sex on motor control strategies.
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Affiliation(s)
- Joshua C Carr
- Texas Christian University, Department of Kinesiology, Fort Worth, TX, United States; Anne Burnett Marion School of Medicine at Texas Christian University, Department of Medical Education, Fort Worth, TX, United States.
| | - Adam C King
- Texas Christian University, Department of Kinesiology, Fort Worth, TX, United States; Anne Burnett Marion School of Medicine at Texas Christian University, Department of Medical Education, Fort Worth, TX, United States.
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Olmos AA, Sterczala AJ, Parra ME, Dimmick HL, Miller JD, Deckert JA, Sontag SA, Gallagher PM, Fry AC, Herda TJ, Trevino MA. Sex-related differences in motor unit behavior are influenced by myosin heavy chain during high- but not moderate-intensity contractions. Acta Physiol (Oxf) 2023; 239:e14024. [PMID: 37551144 DOI: 10.1111/apha.14024] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2022] [Revised: 07/18/2023] [Accepted: 07/19/2023] [Indexed: 08/09/2023]
Abstract
AIMS Motor unit recruitment and firing rate patterns of the vastus lateralis (VL) have not been compared between sexes during moderate- and high-intensity contraction intensities. Additionally, the influence of fiber composition on potential sex-related differences remains unquantified. METHODS Eleven males and 11 females performed 40% and 70% maximal voluntary contractions (MVCs). Surface electromyographic (EMG) signals recorded from the VL were decomposed. Recruitment thresholds (RTs), MU action potential amplitudes (MUAPAMP ), initial firing rates (IFRs), mean firing rates (MFRs), and normalized EMG amplitude (N-EMGRMS ) at steady torque were analyzed. Y-intercepts and slopes were calculated for MUAPAMP , IFR, and MFR versus RT relationships. Type I myosin heavy chain isoform (MHC) was determined with muscle biopsies. RESULTS There were no sex-related differences in MU characteristics at 40% MVC. At 70% MVC, males exhibited greater slopes (p = 0.002) for the MUAPAMP , whereas females displayed greater slopes (p = 0.001-0.007) for the IFR and MFR versus RT relationships. N-EMGRMS at 70% MVC was greater for females (p < 0.001). Type I %MHC was greater for females (p = 0.006), and was correlated (p = 0.018-0.031) with the slopes for the MUAPAMP , IFR, and MFR versus RT relationships at 70% MVC (r = -0.599-0.585). CONCLUSION Both sexes exhibited an inverse relationship between MU firing rates and recruitment thresholds. However, the sex-related differences in MU recruitment and firing rate patterns and N-EMGRMS at 70% MVC were likely due to greater type I% MHC and smaller twitch forces of the higher threshold MUs for the females. Evidence is provided that muscle fiber composition may explain divergent MU behavior between sexes.
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Affiliation(s)
- Alex A Olmos
- Applied Neuromuscular Physiology Lab, Department of Kinesiology, Applied Health, and Recreation, Oklahoma State University, Stillwater, Oklahoma, USA
| | - Adam J Sterczala
- Neuromuscular Research Laboratory, Department of Sports Medicine and Nutrition, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Mandy E Parra
- School of Exercise and Sport Science, University of Mary Hardin-Baylor, Belton, Texas, USA
| | - Hannah L Dimmick
- Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada
| | - Jonathan D Miller
- Department of Chemical and Petroleum Engineering, University of Kansas, Lawrence, Kansas, USA
| | - Jake A Deckert
- Department of Human Physiology, Gonzaga University, Spokane, Washington, USA
| | - Stephanie A Sontag
- Applied Neuromuscular Physiology Lab, Department of Kinesiology, Applied Health, and Recreation, Oklahoma State University, Stillwater, Oklahoma, USA
| | - Philip M Gallagher
- Applied Physiology Laboratory, Department of Health, Sport, and Exercise Sciences, University of Kansas, Lawrence, Kansas, USA
| | - Andrew C Fry
- Jayhawk Athletic Performance Laboratory - Wu Tsai Human Performance Alliance, University of Kansas, Lawrence, Kansas, USA
| | - Trent J Herda
- Neuromechanics Laboratory, Department of Health, Sport, and Exercise Sciences, University of Kansas, Lawrence, Kansas, USA
| | - Michael A Trevino
- Applied Neuromuscular Physiology Lab, Department of Kinesiology, Applied Health, and Recreation, Oklahoma State University, Stillwater, Oklahoma, USA
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Jenz ST, Beauchamp JA, Gomes MM, Negro F, Heckman CJ, Pearcey GEP. Estimates of persistent inward currents in lower limb motoneurons are larger in females than in males. J Neurophysiol 2023; 129:1322-1333. [PMID: 37096909 PMCID: PMC10202474 DOI: 10.1152/jn.00043.2023] [Citation(s) in RCA: 13] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2023] [Revised: 04/02/2023] [Accepted: 04/19/2023] [Indexed: 04/26/2023] Open
Abstract
Noninvasive recordings of motor unit (MU) spike trains help us understand how the nervous system controls movement and how it adapts to various physiological conditions. The majority of participants in human and nonhuman animal physiology studies are male, and it is assumed that mechanisms uncovered in these studies are shared between males and females. However, sex differences in neurological impairment and physical performance warrant the study of sex as a biological variable in human physiology and performance. To begin addressing this gap in the study of biophysical properties of human motoneurons, we quantified MU discharge rates and estimates of persistent inward current (PIC) magnitude in both sexes. We decomposed MU spike trains from the tibialis anterior (TA), medial gastrocnemius (MG), and soleus (SOL) using high-density surface electromyography and blind source separation algorithms. Ten participants of each sex performed slow triangular (10 s up and down) isometric contractions to a peak of 30% of their maximum voluntary contraction. We then used linear mixed-effects models to determine if peak discharge rate and estimates of PICs were predicted by the fixed effects of sex, muscle, and their interaction. Despite a lack of sex-differences in peak discharge rates across all muscles, estimates of PICs were larger [χ2(1) = 6.26, P = 0.012] in females [4.73 ± 0.242 pulses per second (pps)] than in males (3.81 ± 0.240 pps). These findings suggest that neuromodulatory drive, inhibitory input, and/or biophysical properties of motoneurons differ between the sexes and may contribute to differences in MU discharge patterns.NEW & NOTEWORTHY Sex-related differences in motoneuron analyses have emerged with greater inclusion of female participants, however, mechanisms for these differences remain unclear. Estimates of persistent inward currents (i.e., ΔF) in motoneurons of the lower limb muscles were larger in females than in males. This suggests neuromodulatory drive, monoaminergic signaling, intrinsic motoneuron properties, and/or descending motor commands may differ between the sexes, which provides a potential mechanism underlying previously reported sex-related differences in motoneuron discharge patterns.
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Affiliation(s)
- Sophia T Jenz
- Department of Physical Therapy and Human Movement Sciences, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, United States
- Department of Neuroscience, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, United States
| | - James A Beauchamp
- Department of Physical Therapy and Human Movement Sciences, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, United States
- Department of Biomedical Engineering, McCormick School of Engineering, Northwestern University, Evanston, Illinois, United States
| | - Matheus M Gomes
- School of Physical Education and Sport of Ribeirão Preto, University of São Paulo, Ribeirão Preto, Brazil
| | - Francesco Negro
- Department of Clinical and Experimental Sciences, Universita degli Studi di Brescia, Brescia, Italy
| | - C J Heckman
- Department of Physical Therapy and Human Movement Sciences, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, United States
- Department of Neuroscience, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, United States
- Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, United States
- Shirley Ryan AbilityLab, Chicago, Illinois, United States
| | - Gregory E P Pearcey
- Department of Physical Therapy and Human Movement Sciences, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, United States
- School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada
- Division of BioMedical Sciences, Faculty of Medicine, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada
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Gray SM, Cuomo AM, Proppe CE, Traylor MK, Hill EC, Keller JL. Effects of Sex and Cuff Pressure on Physiological Responses during Blood Flow Restriction Resistance Exercise in Young Adults. Med Sci Sports Exerc 2023; 55:920-931. [PMID: 36729632 DOI: 10.1249/mss.0000000000003103] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
PURPOSE The purpose of this study was to examine the physiological responses resulting from an acute blood flow restriction resistance exercise bout with two different cuff pressures in young, healthy men and women. METHODS Thirty adults (18-30 yr) completed a bilateral leg extension blood flow restriction bout consisting of four sets (30-15-15-15 repetitions), with cuffs applied at pressures corresponding to 40% and 60% of the minimum arterial occlusion pressure (AOP) needed to completely collapse the femoral arteries. During each of these conditions (40% and 60% AOP), physiological measures of near-infrared spectroscopy (NIRS) and EMG amplitude (EMG AMP) were collected from the dominant or nondominant vastus lateralis. After each set, ratings of perceived exertion (RPE) were collected, whereas only at baseline and at the end of the bout, mean arterial pressure (MAP) was assessed. Separate mixed-factorial ANOVA models were used to examine mean differences in the change in EMG AMP and NIRS parameters during each set. The absolute RPE and MAP values were also examined with separate ANOVAs. A P value ≤0.05 was considered statistically significant. RESULTS Regardless of sex or cuff pressure, the change in EMG AMP was lower in set 1 (14.8%) compared with the remaining sets (22.6%-27.0%). The 40% AOP condition elicited the greatest changes in oxy[heme] and deoxy[heme], while also providing lower RPEs. For MAP, there was an effect for time such that MAP increased from preexercise (87.5 ± 4.3 mm Hg) to postexercise (104.5 ± 4.1 mm Hg). CONCLUSIONS The major findings suggested that the 40% AOP condition permitted the greatest amount of recovery during the interset rest. In addition, there did not seem to be any meaningful sex-related difference in this sample of young healthy adults.
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Affiliation(s)
- Sylvie M Gray
- Integrated Laboratory of Exercise and Applied Physiology (iLEAP), Department of Health, Kinesiology and Sport, College of Education and Professional Studies, University of South Alabama, Mobile, AL
| | | | - Christopher E Proppe
- Division of Kinesiology, School of Kinesiology and Physical Therapy, University of Central Florida, Orlando, FL
| | - Miranda K Traylor
- Integrated Laboratory of Exercise and Applied Physiology (iLEAP), Department of Health, Kinesiology and Sport, College of Education and Professional Studies, University of South Alabama, Mobile, AL
| | | | - Joshua L Keller
- Integrated Laboratory of Exercise and Applied Physiology (iLEAP), Department of Health, Kinesiology and Sport, College of Education and Professional Studies, University of South Alabama, Mobile, AL
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Lulic-Kuryllo T, Greig Inglis J. Sex differences in motor unit behaviour: A review. J Electromyogr Kinesiol 2022; 66:102689. [DOI: 10.1016/j.jelekin.2022.102689] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2021] [Revised: 07/28/2022] [Accepted: 07/29/2022] [Indexed: 10/15/2022] Open
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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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Keller JL, Anders JPV, Neltner TJ, Housh TJ, Schmidt RJ, Johnson GO. Sex differences in muscle excitation and oxygenation, but not in force fluctuations or active hyperemia resulting from a fatiguing, bilateral isometric task. Physiol Meas 2021; 42. [PMID: 34847546 DOI: 10.1088/1361-6579/ac3e86] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2021] [Accepted: 11/30/2021] [Indexed: 01/25/2023]
Abstract
It remains to be fully elucidated if there are sex-specific physiological adjustments within the human neuromuscular and vascular systems that contribute to symptoms of fatigue during a sustained bilateral task. This, in part, is likely due to various limitations in experimental design such as an inability to independently record force fluctuations from each limb.Objective. Therefore, the purpose of the current study was to examine the fatigue-induced changes in muscle excitation, force fluctuations, skeletal muscle tissue saturation (StO2), and muscle blood flow resulting from a sustained, bilateral task.Approach. Thirty healthy, college-aged adults (15 males, 15 females) performed a bilateral leg task at 25% of maximum voluntary isometric (MVIC). Before and after the task, MVICs were completed. Resting and post-task femoral artery blood flow (FABF) were determined. Muscle excitation was quantified as electromyographic amplitude (EMG AMP) from the right and left vastus lateralis. During the task, force fluctuations were determined independently from each leg. The StO2signal was collected with a near-infrared spectroscopy device attached to the right vastus lateralis. The rate of change in these variables was calculated via simple linear regression. The exercise-induced magnitude of change in MVIC (i.e. performance fatigability) and FABF (i.e. active hyperemia) was determined.Main Results. There was no sex difference in the percent decline in MVIC (20.5 ± 20.1% versus 16.4 ± 3.5%;p> 0.05). There were no inter-leg differences in EMG AMP or force fluctuations. The males exhibited a faster rate of increase in EMG AMP (b= 0.13 versusb= 0.08;p< 0.001), whereas the females exhibited a slower rate of decline in StO2(b= -0.049 versusb= -0.080). There was no sex difference in force fluctuations or change in FABF.Significance. Males and females likely have different neuromuscular strategies and muscle characteristics, but these did not elicit a sex difference in performance fatigability.
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Affiliation(s)
- Joshua L Keller
- Integrative Laboratory of Exercise and Applied Physiology (iLEAP), Department of Health, Kinesiology, and Sport, College of Education and Professional Studies, University of South Alabama, Mobile, AL 36606, United States of America
| | - John Paul V Anders
- Exercise Physiology Laboratory, Department of Nutrition and Health Sciences, College of Education, University of Nebraska-Lincoln, Lincoln, NE 68588, United States of America
| | - Tyler J Neltner
- Exercise Physiology Laboratory, Department of Nutrition and Health Sciences, College of Education, University of Nebraska-Lincoln, Lincoln, NE 68588, United States of America
| | - Terry J Housh
- Exercise Physiology Laboratory, Department of Nutrition and Health Sciences, College of Education, University of Nebraska-Lincoln, Lincoln, NE 68588, United States of America
| | - Richard J Schmidt
- Exercise Physiology Laboratory, Department of Nutrition and Health Sciences, College of Education, University of Nebraska-Lincoln, Lincoln, NE 68588, United States of America
| | - Glen O Johnson
- Exercise Physiology Laboratory, Department of Nutrition and Health Sciences, College of Education, University of Nebraska-Lincoln, Lincoln, NE 68588, United States of America
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Men exhibit faster skeletal muscle tissue desaturation than women before and after a fatiguing handgrip. Eur J Appl Physiol 2021; 121:3473-3483. [PMID: 34515868 PMCID: PMC8436195 DOI: 10.1007/s00421-021-04810-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2021] [Accepted: 09/07/2021] [Indexed: 11/22/2022]
Abstract
Purpose The purpose was to test the hypothesis that sex and fatigue effect of the early phase of skeletal muscle tissue oxygenation (StO2, %) desaturation rate as well as that strength matched adults may exhibit similar responses. Methods Twenty-four adults visited the laboratory twice to quantify this early phase of desaturation during vascular occlusion tests (VOT) while in a rested state. The second visit included a sustained handgrip task at 25% of maximal muscular strength until task failure. At failure, a post-task VOT was initiated. Muscle desaturation was defined as StO2 and collected by a near-infrared spectroscopy device. The muscle size and adipose thickness were determined via ultrasonography. Linear regression was used to quantify the rates of desaturation during the VOTs as well as during the fatiguing handgrip. Results There were sex differences in the rate of desaturation pre- and post-handgrip, such that independent of fatigue, the men (p < 0.001) desaturated more rapidly than the women (pre: b = − 0.208 vs. − 0.123%∙s−1; post: − 0.079 vs. − 0.070%∙s−1). During the fatiguing handgrip, the transformed StO2 values indicated that the males desaturated more rapidly than the females (b = − 0.070 vs. − 0.015). The matched pairs exhibited the same responses as the total sample. Conclusion Overall, muscle size and strength as well as adipose tissue were likely not the primary cause of the differences in rates of muscle desaturation. We hypothesized that differences in fiber type and mitochondria were the principle mechanisms provoking the differences in muscle oxygenation.
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The relationship of agonist muscle single motor unit firing rates and elbow extension limb movement kinematics. Exp Brain Res 2021; 239:2755-2766. [PMID: 34240233 DOI: 10.1007/s00221-021-06168-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2021] [Accepted: 06/26/2021] [Indexed: 10/20/2022]
Abstract
This study explored the relationship between single motor unit (MU) firing rates (FRs) and limb movement velocity during voluntary shortening contractions when accounting for the effects of time course variability between different kinematic comparisons. Single MU trains recorded by intramuscular electromyography in agonist muscles of the anconeus (n = 15 participants) and lateral head of the triceps brachii (n = 6) were measured during each voluntary shortening contraction. Elbow extension movements consisted of a targeted velocity occurring along the sagittal plane at 25, 50, 75 and 100% of maximum velocity. To account for the effect of differences in contraction time course between parameters, each MU potential was time locked throughout the shortening muscle contraction and linked with separated kinematic parameters of the elbow joint. Across targeted movement velocities, instantaneous FRs were significantly correlated with elbow extension rate of torque development (r = 0.45) and torque (r = 0.40), but FRs were not correlated with velocity (r = 0.03, p = n.s.). Instead, FRs had a weak indirect relationship with limb movement velocity and position assessed through multiple correlation of the stepwise kinematic progression. Results show that voluntary descending synaptic inputs correspond to a more direct relationship between agonist muscle FRs and torque during shortening contractions, but not velocity. Instead, FRs were indirectly correlated to preparing the magnitude of imminent movement velocity of the lagging limb through torque.
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Reece TM, Herda TJ. An examination of a potential organized motor unit firing rate and recruitment scheme of an antagonist muscle during isometric contractions. J Neurophysiol 2021; 125:2094-2106. [PMID: 33909509 DOI: 10.1152/jn.00034.2021] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The primary purpose of the present study is to determine if an organized control scheme exists for the antagonist muscle during steady isometric torque. A secondary focus is to better understand how firing rates of the antagonist muscle change from a moderate- to higher-contraction intensity. Fourteen subjects performed two submaximal isometric trapezoid muscle actions of the forearm flexors that included a linearly increasing, steady force at both 40% and 70% maximum voluntary contraction, and linearly decreasing segments. Surface electromyographic signals of the biceps and triceps brachii were collected and decomposed into constituent motor unit action potential trains. Motor unit firing rate versus recruitment threshold, motor unit action potential amplitude versus recruitment threshold, and motor unit firing rate versus action potential amplitude relationships of the biceps brachii (agonist) and triceps brachii (antagonist) muscles were analyzed. Moderate- to-strong relationships (|r| ≥ 0.69) were present for the agonist and antagonist muscles for each relationship with no differences between muscles (P = 0.716, 0.428, 0.182). The y-intercepts of the motor unit firing rate versus recruitment threshold relationship of the antagonist did not increase from 40% to 70% maximal voluntary contractions (P = 0.96), unlike for the agonist (P = 0.009). The antagonist muscle exhibits a similar motor unit control scheme to the agonist. Unlike the agonist, however, the firing rates of the antagonist did not increase with increasing intensity. Future research should investigate how antagonist firing rates adapt to resistance training and changes in antagonist firing rates in the absence of peripheral feedback.NEW & NOTEWORTHY This is the first study to explore a potential motor unit control scheme and quantify changes in firing rates with increasing intensity of an antagonist muscle during isometric contractions. We demonstrate that the antagonist muscle possesses an organized motor unit firing rate and recruitment scheme similar to the agonist muscle during isometric forearm flexion, but unlike the agonist muscle, there was no significant increase in firing rates from a moderate- to higher-intensity isometric contraction.
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Affiliation(s)
- Tanner M Reece
- Neuromechanics Laboratory, Department of Health, Sport and Exercise Sciences, University of Kansas, Lawrence, Kansas
| | - Trent J Herda
- Neuromechanics Laboratory, Department of Health, Sport and Exercise Sciences, University of Kansas, Lawrence, Kansas
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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] [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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