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Papavasileiou A, Xenofondos A, Baudry S, Lapole T, Amiridis IG, Metaxiotis D, Tsatalas T, Patikas DA. Protocols Targeting Afferent Pathways via Neuromuscular Electrical Stimulation for the Plantar Flexors: A Systematic Review. SENSORS (BASEL, SWITZERLAND) 2023; 23:2347. [PMID: 36850945 PMCID: PMC9967278 DOI: 10.3390/s23042347] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/30/2022] [Revised: 02/02/2023] [Accepted: 02/17/2023] [Indexed: 06/18/2023]
Abstract
This systematic review documents the protocol characteristics of studies that used neuromuscular electrical stimulation protocols (NMES) on the plantar flexors [through triceps surae (TS) or tibial nerve (TN) stimulation] to stimulate afferent pathways. The review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) statement, was registered to PROSPERO (ID: CRD42022345194) and was funded by the Greek General Secretariat for Research and Technology (ERA-NET NEURON JTC 2020). Included were original research articles on healthy adults, with NMES interventions applied on TN or TS or both. Four databases (Cochrane Library, PubMed, Scopus, and Web of Science) were systematically searched, in addition to a manual search using the citations of included studies. Quality assessment was conducted on 32 eligible studies by estimating the risk of bias with the checklist of the Effective Public Health Practice Project Quality Assessment Tool. Eighty-seven protocols were analyzed, with descriptive statistics. Compared to TS, TN stimulation has been reported in a wider range of frequencies (5-100, vs. 20-200 Hz) and normalization methods for the contraction intensity. The pulse duration ranged from 0.2 to 1 ms for both TS and TN protocols. It is concluded that with increasing popularity of NMES protocols in intervention and rehabilitation, future studies may use a wider range of stimulation attributes, to stimulate motor neurons via afferent pathways, but, on the other hand, additional studies may explore new protocols, targeting for more optimal effectiveness. Furthermore, future studies should consider methodological issues, such as stimulation efficacy (e.g., positioning over the motor point) and reporting of level of discomfort during the application of NMES protocols to reduce the inherent variability of the results.
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Affiliation(s)
- Anastasia Papavasileiou
- Laboratory of Neuromechanics, School of Physical Education and Sports Science at Serres, Aristotle University of Thessaloniki, 62110 Serres, Greece
| | - Anthi Xenofondos
- Physical Education and Sports Sciences, Frederick University, 1036 Nicosia, Cyprus
| | - Stéphane Baudry
- Laboratory of Applied Biology, Research Unit in Applied Neurophysiology (LABNeuro), Université Libre de Bruxelles, 1070 Brussels, Belgium
| | - Thomas Lapole
- Université Jean Monnet Saint-Etienne, Lyon 1, Université Savoie Mont-Blanc, Laboratoire Interuniversitaire de Biologie de la Motricité, F-42023 Saint-Etienne, France
| | - Ioannis G. Amiridis
- Laboratory of Neuromechanics, School of Physical Education and Sports Science at Serres, Aristotle University of Thessaloniki, 62110 Serres, Greece
| | | | - Themistoklis Tsatalas
- Department of Physical Education and Sport Science, University of Thessaly, 42100 Trikala, Greece
| | - Dimitrios A. Patikas
- Laboratory of Neuromechanics, School of Physical Education and Sports Science at Serres, Aristotle University of Thessaloniki, 62110 Serres, Greece
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Hadjizadeh Anvar S, Kordi MR, Alizadeh S, Ramsay E, Shabkhiz F, Behm DG. Lack of Evidence for Crossover Fatigue with Plantar Flexor Muscles. J Sports Sci Med 2022; 21:214-223. [PMID: 35719232 PMCID: PMC9157513 DOI: 10.52082/jssm.2022.214] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2022] [Accepted: 04/01/2022] [Indexed: 06/15/2023]
Abstract
The occurrence and mechanisms underlying non-local or crossover muscle fatigue is an ongoing issue. This study aimed to investigate crossover fatigue of the plantar flexor muscles. Sixteen recreationally active males (n = 6) and females (n = 10) visited the laboratory for four sessions and performed a single 5-s pre-test maximal voluntary isometric contraction (MVIC) with each plantar flexors muscle. Thereafter, the fatigue intervention involved two 100-s MVICs (60-s recovery) with their dominant plantar flexors or rested for 260-s (control). Subsequently, in two separate sessions, Hoffman reflexes (H-reflex) were evoked in the non-dominant, non-exercised, leg before and following the dominant leg fatigue or control intervention (Fatigue-Reflex and Control-Reflex conditions). MVIC forces and volitional (V)-waves were monitored in the non-dominant leg in the other two sessions (Fatigue-MVIC and Control-MVIC) before and after the intervention (fatigue or control) as well as during 12 repeated MVICs and immediately thereafter. Despite the force reduction in the dominant leg (42.4%, p = 0.002), no crossover force deficit with single (F(1,9) = 0.02, p = 0.88, pƞ2 = 0.003) or repeated (F(1,9) = 0.006, p = 0.93, pƞ2 = 0.001) MVIC testing were observed. The H-reflex did not change after the fatigue (F(1,7) = 0.51; p = 0.49; pƞ2 = 0.06) or repeated MVICs (F(1,8) = 0.27; p = 0.61; pƞ2 = 0.03). There were also no crossover effects of fatigue on the V-wave with single (F(1,8) = 3.71, p = 0.09, pƞ2 = 0.31) or repeated MVICs (F(1,6) = 1.45, p = 0.27, pƞ2 = 0.19). Crossover fatigue was not evident with the plantar flexors nor any significant changes in H-reflex and V-waves in the soleus muscle. This finding suggests that crossover fatigue may not necessarily occur in slow-twitch predominant muscle groups.
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Affiliation(s)
- Saman Hadjizadeh Anvar
- School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John's Newfoundland and Labrador (NL), Canada
- Faculty of Physical Education & Sport Sciences, University of Tehran, Tehran, Iran
| | - Mohammad Reza Kordi
- Faculty of Physical Education & Sport Sciences, University of Tehran, Tehran, Iran
| | - Shahab Alizadeh
- School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John's Newfoundland and Labrador (NL), Canada
| | - Emma Ramsay
- School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John's Newfoundland and Labrador (NL), Canada
| | - Fatemeh Shabkhiz
- Faculty of Physical Education & Sport Sciences, University of Tehran, Tehran, Iran
| | - David G Behm
- School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John's Newfoundland and Labrador (NL), Canada
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Kobak KA, Lawrence MM, Pharaoh G, Borowik AK, Peelor FF, Shipman PD, Griffin TM, Van Remmen H, Miller BF. Determining the contributions of protein synthesis and breakdown to muscle atrophy requires non-steady-state equations. J Cachexia Sarcopenia Muscle 2021; 12:1764-1775. [PMID: 34418329 PMCID: PMC8718081 DOI: 10.1002/jcsm.12772] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/10/2021] [Revised: 06/17/2021] [Accepted: 07/10/2021] [Indexed: 01/29/2023] Open
Abstract
BACKGROUND Ageing and cachexia cause a loss of muscle mass over time, indicating that protein breakdown exceeds protein synthesis. Deuterium oxide (D2 O) is used for studies of protein turnover because of the advantages of long-term labelling, but these methods introduce considerations that have been largely overlooked when studying conditions of protein gain or loss. The purpose of this study was to demonstrate the importance of accounting for a change in protein mass, a non-steady state, during D2 O labelling studies while also exploring the contribution of protein synthesis and breakdown to denervation-induced muscle atrophy. METHODS Adult (6 months) male C57BL/6 mice (n = 14) were labelled with D2 O for a total of 7 days following unilateral sciatic nerve transection to induce denervation of hindlimb muscles. The contralateral sham limb and nonsurgical mice (n = 5) were used as two different controls to account for potential crossover effects of denervation. We calculated gastrocnemius myofibrillar and collagen protein synthesis and breakdown assuming steady-state or using non-steady-state modelling. We measured RNA synthesis rates to further understand ribosomal turnover during atrophy. RESULTS Gastrocnemius mass was less in denervated muscle (137 ± 9 mg) compared with sham (174 ± 15 mg; P < 0.0001) or nonsurgical control (162 ± 5 mg; P < 0.0001). With steady-state calculations, fractional synthesis and breakdown rates (FSR and FBR) were lower in the denervated muscle (1.49 ± 0.06%/day) compared with sham (1.81 ± 0.09%/day; P < 0.0001) or nonsurgical control (2.27 ± 0.04%/day; P < 0.0001). When adjusting for change in protein mass, FSR was 4.21 ± 0.19%/day in denervated limb, whereas FBR was 4.09 ± 0.22%/day. When considering change in protein mass (ksyn ), myofibrillar synthesis was lower in denervated limb (2.44 ± 0.14 mg/day) compared with sham (3.43 ± 0.22 mg/day; P < 0.0001) and non-surgical control (3.74 ± 0.12 mg/day; P < 0.0001), whereas rate of protein breakdown (kdeg, 1/t) was greater in denervated limb (0.050 ± 0.003) compared with sham (0.019 ± 0.001; P < 0.0001) and nonsurgical control (0.023 ± 0.000; P < 0.0001). Muscle collagen breakdown was completely inhibited during denervation. There was a strong correlation (r = 0.83, P < 0.001) between RNA and myofibrillar protein synthesis in sham but not denervated muscle. CONCLUSIONS We show conflicting results between steady- and non-steady-state calculations on myofibrillar protein synthesis and breakdown during periods of muscle loss. We also found that collagen accumulation was largely from a decrease in collagen breakdown. Comparison between sham and non-surgical control demonstrated a crossover effect of denervation on myofibrillar protein synthesis and ribosomal biogenesis, which impacts study design for unilateral atrophy studies. These considerations are important because not accounting for them can mislead therapeutic attempts to maintain muscle mass.
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Affiliation(s)
- Kamil A Kobak
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK, USA.,Laboratory for Applied Research on Cardiovascular System, Department of Heart Diseases, Wroclaw Medical University, Wroclaw, Poland
| | - Marcus M Lawrence
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK, USA.,Department of Kinesiology and Outdoor Recreation, Southern Utah University, Cedar City, UT, USA
| | - Gavin Pharaoh
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK, USA
| | - Agnieszka K Borowik
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK, USA
| | - Frederick F Peelor
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK, USA
| | - Patrick D Shipman
- Department of Mathematics, Colorado State University, Fort Collins, CO, USA
| | - Timothy M Griffin
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK, USA.,Oklahoma City VA Medical Center, Oklahoma City, OK, USA
| | - Holly Van Remmen
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK, USA.,Oklahoma City VA Medical Center, Oklahoma City, OK, USA
| | - Benjamin F Miller
- Aging and Metabolism Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK, USA
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Enoka RM, Amiridis IG, Duchateau J. Electrical Stimulation of Muscle: Electrophysiology and Rehabilitation. Physiology (Bethesda) 2020; 35:40-56. [DOI: 10.1152/physiol.00015.2019] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The generation of action potentials in intramuscular motor and sensory axons in response to an imposed external current source can evoke muscle contractions and elicit widespread responses throughout the nervous system that impact sensorimotor function. The benefits experienced by individuals exposed to several weeks of treatment with electrical stimulation of muscle suggest that the underlying adaptations involve several physiological systems, but little is known about the specific changes elicited by such interventions.
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Affiliation(s)
- Roger M. Enoka
- Department of Integrative Physiology, University of Colorado Boulder, Colorado
| | - Ioannis G. Amiridis
- Department of Physical Education and Sport Sciences at Serres, Aristotle University of Thessaloniki, Thessaloniki, Greece
| | - Jacques Duchateau
- Laboratory of Applied Biology and Neurophysiology, ULB Neuroscience Institute, Université Libre de Bruxelles, Brussels, Belgium
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Liu H, Thompson LV. Skeletal muscle denervation investigations: selecting an experimental control wisely. Am J Physiol Cell Physiol 2019; 316:C456-C461. [PMID: 30624984 PMCID: PMC6457105 DOI: 10.1152/ajpcell.00441.2018] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Unilateral denervation is widely used for studies investigating mechanisms of muscle atrophy. The “contralateral-innervated muscle” is a commonly used experimental control in denervation studies. It is not clear whether denervation unilaterally alters the proteolytic system in the contralateral-innervated muscles. Therefore, the objectives of this rapid report are 1) to determine whether unilateral denervation has an effect on the proteolytic system in contralateral-innervated control muscles and 2) to identify the changes in proteasome properties in denervated muscles after 7- and 14-day tibial nerve transection with either the contralateral-innervated muscles or intact muscles from nonsurgical mice used as the experimental control. In the contralateral-innervated muscles after 7 and 14 days of nerve transection, the proteasome activities and content are significantly increased compared with muscles from nonsurgical mice. When the nonsurgical mice are used as the experimental control, a robust increase in proteasome properties is found in the denervated muscles. This robust increase in proteasome properties is eliminated when the contralateral-innervated muscles are the experimental control. In conclusion, there is a crossover effect from unilateral denervation on proteolytic parameters. As a result, the crossover effect on contralateral-innervated muscles must be considered when an experimental control is selected in a denervation study.
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Affiliation(s)
- Haiming Liu
- Division of Gerontology and Geriatric Medicine, Department of Medicine, School of Medicine, University of Washington, and Geriatric Research, Education, and Clinical Center, Veterans Affairs Puget Sound Healthcare System, Seattle, Washington
| | - LaDora V Thompson
- Department of Physical Therapy and Athletic Training, Boston University , Boston, Massachusetts
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Hamilton LD, Mani D, Almuklass AM, Davis LA, Vieira T, Botter A, Enoka RM. Electrical nerve stimulation modulates motor unit activity in contralateral biceps brachii during steady isometric contractions. J Neurophysiol 2018; 120:2603-2613. [PMID: 30156959 DOI: 10.1152/jn.00235.2018] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The purpose of our study was to compare the influence of five types of electrical nerve stimulation delivered through electrodes placed over the right biceps brachii on motor unit activity in the left biceps brachii during an ongoing steady isometric contraction. The electrical stimulation protocols comprised different combinations of pulse duration (0.2 and 1.0 ms), stimulus frequency (50 and 90 Hz), and stimulus current (greater or less than motor threshold). The electrical nerve stimulation protocols were applied over the muscle of the right elbow flexors of 13 participants (26 ± 3 yr) while they performed voluntary contractions with the left elbow flexors to match a target force set at 10% of maximum. All five types of electrical nerve stimulation increased the absolute amplitude of the electromyographic (EMG) signal recorded from the left biceps brachii with high-density electrodes. Moreover, one stimulation condition (1 ms, 90 Hz) had a consistent influence on the centroid location of the EMG amplitude distribution and the average force exerted by the left elbow flexors. Another stimulation condition (0.2 ms, 90 Hz) reduced the coefficient of variation for force during the voluntary contraction, and both low-frequency conditions (50 Hz) increased the duration of the mean interspike interval of motor unit action potentials after the stimulation had ended. The findings indicate that the contralateral effects of electrical nerve stimulation on the motor neuron pool innervating the homologous muscle can be influenced by both stimulus pulse duration and stimulus frequency. NEW & NOTEWORTHY Different types of electrical nerve stimulation delivered through electrodes placed over the right biceps brachii modulated the ongoing motor unit activity in the left biceps brachii. Although the effects varied with stimulus pulse duration, frequency, and current, all five types of electrical nerve stimulation increased the amplitude of the electromyographic activity in the left biceps brachii. Moreover, most of the effects in the left arm occurred after the electrical nerve stimulation of the right arm had been terminated.
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Affiliation(s)
- Landon D Hamilton
- Department of Integrative Physiology, University of Colorado , Boulder, Colorado
| | - Diba Mani
- Department of Integrative Physiology, University of Colorado , Boulder, Colorado
| | - Awad M Almuklass
- Department of Integrative Physiology, University of Colorado , Boulder, Colorado.,College of Medicine, King Saud bin Abdulaziz University for Health Sciences , Riyadh , Saudi Arabia
| | - Leah A Davis
- Department of Integrative Physiology, University of Colorado , Boulder, Colorado
| | - Taian Vieira
- LISiN, Department of Electronics and Telecommunications, Politecnico di Torino, Torino , Italy
| | - Alberto Botter
- LISiN, Department of Electronics and Telecommunications, Politecnico di Torino, Torino , Italy
| | - Roger M Enoka
- Department of Integrative Physiology, University of Colorado , Boulder, Colorado
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Miller BF, Hamilton KL, Majeed ZR, Abshire SM, Confides AL, Hayek AM, Hunt ER, Shipman P, Peelor FF, Butterfield TA, Dupont‐Versteegden EE. Enhanced skeletal muscle regrowth and remodelling in massaged and contralateral non-massaged hindlimb. J Physiol 2018; 596:83-103. [PMID: 29090454 PMCID: PMC5746529 DOI: 10.1113/jp275089] [Citation(s) in RCA: 49] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Accepted: 10/16/2017] [Indexed: 12/21/2022] Open
Abstract
KEY POINTS Muscle fibre cross sectional area is enhanced with massage in the form of cyclic compressive loading during regrowth after atrophy. Massage enhances protein synthesis of the myofibrillar and cytosolic, but not the mitochondrial fraction, in muscle during regrowth. Focal adhesion kinase activation and satellite cell number are elevated in muscles undergoing massage during regrowth. Muscle fibre cross sectional area and protein synthesis of the myofibrillar fraction, but not DNA synthesis, are elevated in muscle of the contralateral non-massaged limb. Massage in the form of cyclic compressive loading is a potential anabolic intervention during muscle regrowth after atrophy. ABSTRACT Massage, in the form of cyclic compressive loading (CCL), is associated with multiple health benefits, but its potential anabolic effect on atrophied muscle has not been investigated. We hypothesized that the mechanical activity associated with CCL induces an anabolic effect in skeletal muscle undergoing regrowth after a period of atrophy. Fischer-Brown Norway rats at 10 months of age were hindlimb unloaded for a period of 2 weeks. The rats were then allowed reambulation with CCL applied at a 4.5 N load at 0.5 Hz frequency for 30 min every other day for four bouts during a regrowth period of 8 days. Muscle fibre cross sectional area was enhanced by 18% with massage during regrowth compared to reloading alone, and this was accompanied by elevated myofibrillar and cytosolic protein as well as DNA synthesis. Focal adhesion kinase phosphorylation indicated that CCL increased mechanical stimulation, while a higher number of Pax7+ cells likely explains the elevated DNA synthesis. Surprisingly, the contralateral non-massaged limb exhibited a comparable 17% higher muscle fibre size compared to reloading alone, and myofibrillar protein synthesis, but not DNA synthesis, was also elevated. We conclude that massage in the form of CCL induces an anabolic response in muscles regrowing after an atrophy-inducing event. We suggest that massage can be used as an intervention to aid in the regrowth of muscle lost during immobilization.
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Affiliation(s)
- Benjamin F. Miller
- Health and Exercise ScienceColorado State UniversityFort CollinsCO80523‐1582USA
| | - Karyn L. Hamilton
- Health and Exercise ScienceColorado State UniversityFort CollinsCO80523‐1582USA
| | - Zana R. Majeed
- Department of Rehabilitation Sciences, College of Health SciencesUniversity of KentuckyLexingtonKY40536‐0200USA
| | - Sarah M. Abshire
- Department of Rehabilitation Sciences, College of Health SciencesUniversity of KentuckyLexingtonKY40536‐0200USA
- Center for Muscle BiologyUniversity of KentuckyLexingtonKY40536‐0200USA
| | - Amy L. Confides
- Department of Rehabilitation Sciences, College of Health SciencesUniversity of KentuckyLexingtonKY40536‐0200USA
- Center for Muscle BiologyUniversity of KentuckyLexingtonKY40536‐0200USA
| | - Amanda M. Hayek
- Department of Rehabilitation Sciences, College of Health SciencesUniversity of KentuckyLexingtonKY40536‐0200USA
| | - Emily R. Hunt
- Department of Rehabilitation Sciences, College of Health SciencesUniversity of KentuckyLexingtonKY40536‐0200USA
| | - Patrick Shipman
- Department of MathematicsColorado State UniversityFort CollinsCO80523‐1582USA
| | - Frederick F. Peelor
- Health and Exercise ScienceColorado State UniversityFort CollinsCO80523‐1582USA
| | - Timothy A. Butterfield
- Department of Rehabilitation Sciences, College of Health SciencesUniversity of KentuckyLexingtonKY40536‐0200USA
- Center for Muscle BiologyUniversity of KentuckyLexingtonKY40536‐0200USA
| | - Esther E. Dupont‐Versteegden
- Department of Rehabilitation Sciences, College of Health SciencesUniversity of KentuckyLexingtonKY40536‐0200USA
- Center for Muscle BiologyUniversity of KentuckyLexingtonKY40536‐0200USA
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Amiridis IG, Mani D, Almuklass A, Matkowski B, Gould JR, Enoka RM. Modulation of motor unit activity in biceps brachii by neuromuscular electrical stimulation applied to the contralateral arm. J Appl Physiol (1985) 2015; 118:1544-52. [PMID: 25930023 PMCID: PMC4469921 DOI: 10.1152/japplphysiol.00031.2015] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2015] [Accepted: 04/22/2015] [Indexed: 01/06/2023] Open
Abstract
The purpose of the study was to determine the influence of neuromuscular electrical stimulation (NMES) current intensity and pulse width applied to the right elbow flexors on the discharge characteristics of motor units in the left biceps brachii. Three NMES current intensities were applied for 5 s with either narrow (0.2 ms) or wide (1 ms) stimulus pulses: one at 80% of motor threshold and two that evoked contractions at either ∼10% or ∼20% of maximal voluntary contraction (MVC) force. The discharge times of 28 low-threshold (0.4-21.6% MVC force) and 16 high-threshold (31.7-56.3% MVC force) motor units in the short head of biceps brachii were determined before, during, and after NMES. NMES elicited two main effects: one involved transient deflections in the left-arm force at the onset and offset of NMES and the other consisted of nonuniform modulation of motor unit activity. The force deflections, which were influenced by NMES current intensity and pulse width, were observed only when low-threshold motor units were tracked. NMES did not significantly influence the discharge characteristics of tracked single-threshold motor units. However, a qualitative analysis indicated that there was an increase in the number of unique waveforms detected during and after NMES. The findings indicate that activity of motor units in the left elbow flexors can be modulated by NMES current and pulse width applied to right elbow flexors, but the effects are not distributed uniformly to the involved motor units.
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Affiliation(s)
- Ioannis G Amiridis
- Department of Physical Education and Sport Sciences at Serres, Aristotle University of Thessaloniki, Thessaloniki, Greece;
| | - Diba Mani
- Department of Integrative Physiology, University of Colorado, Boulder, Colorado; and
| | - Awad Almuklass
- Department of Integrative Physiology, University of Colorado, Boulder, Colorado; and Department of Basic Medical Sciences, King Saud bin Abdulaziz University for Health Sciences, Riyadh, Saudi Arabia
| | - Boris Matkowski
- Department of Integrative Physiology, University of Colorado, Boulder, Colorado; and
| | - Jeffrey R Gould
- Department of Integrative Physiology, University of Colorado, Boulder, Colorado; and
| | - Roger M Enoka
- Department of Integrative Physiology, University of Colorado, Boulder, Colorado; and
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