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Magnuson JR, Dalton BH, McNeil CJ. Differential Modulation of Motor Unit Behavior When a Fatiguing Contraction Is Matched for Torque versus EMG. Med Sci Sports Exerc 2024; 56:1480-1487. [PMID: 38595197 DOI: 10.1249/mss.0000000000003434] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/11/2024]
Abstract
INTRODUCTION When an isometric contraction is sustained at a submaximal torque, activation of the motoneuron pool increases, making it difficult to interpret neural excitability alterations. Thus, more recently, isometric contractions with maintained electromyographic (EMG) activity (matched-EMG) are being used to induce fatigue; however, little is known about the neurophysiological adjustments that occur to satisfy the requirements of the task. METHODS For our study, 16 participants performed a 10-min sustained isometric elbow flexion contraction at 20% maximal voluntary contraction (MVC) torque or the level of integrated biceps brachii EMG recorded at 20% MVC torque. Surface EMG was used to assess global median frequency, and four fine-wire electrode pairs were used to obtain motor unit (MU) discharge rate from biceps brachii. Torque or EMG steadiness was also assessed throughout the fatiguing contractions. RESULTS MU discharge rate increased and torque steadiness decreased during the matched-torque contraction; however, MU discharge rate decreased during the matched-EMG contraction, and no changes occurred for EMG steadiness. Data pooled for the two contractions revealed a decrease in global median frequency. Lastly, a greater loss of MVC torque was observed immediately after the matched-torque compared with matched-EMG contraction. CONCLUSIONS These findings indicate that, during a matched-torque fatiguing contraction, the nervous system increases MU discharge rates at the cost of poorer steadiness to maintain the requisite torque. In contrast, during a matched-EMG fatiguing contraction, a reduction of MU discharge rates allows for maintenance of EMG steadiness.
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Affiliation(s)
- Justine R Magnuson
- School of Health and Exercise Sciences and Centre for Heart, Lung and Vascular Health, The University of British Columbia, Kelowna, BC, CANADA
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Akbulut AS, Akca Karpuzoglu AH. Evaluation of Temporomandibular Joint in Patients with Parkinson's Disease: A Comparative Study. Diagnostics (Basel) 2023; 13:2482. [PMID: 37568844 PMCID: PMC10416915 DOI: 10.3390/diagnostics13152482] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Revised: 07/11/2023] [Accepted: 07/19/2023] [Indexed: 08/13/2023] Open
Abstract
(1) The aim of this study was to perform an evaluation of the temporomandibular joint (TMJ) in patients with Parkinson's disease (PD) and present the morphological differences of the TMJ between healthy subjects and patients with PD. (2) A total of 102 Caucasian subjects were divided equally into two groups. The study group consisted of patients with PD, while the control group comprised healthy subjects. Ten parameters, including anterior joint space (AJS), superior joint space (SJS), posterior joint space (PJS), condyle head length (CHL), condylar neck width (CNW), minor axis of the condyle (MAC), long axis of the condyle (LAC), condylar axis inclination (CI), medial joint space (MJS), and lateral joint space (LJS), were measured using magnetic resonance images. The data were statistically analyzed using paired samples t-test and Student's t-test, with a significance level set at p < 0.05. (3) In the PD group, all TMJ parameters showed a statistically significant difference between both sides of the face (p < 0.05). However, in the control group, AJS, SJS, PJS, CHL, CNW, MAC, CI, MJS, and LJS did not show a statistically significant difference between both sides of the face (p > 0.05), except for LAC (p < 0.05). The asymmetry index values of AJS, SJS, PJS, CHL, CNW, MAC, CI, MJS, and LJS demonstrated a statistically significant difference between the study and control groups (p < 0.05), except for LAC (p > 0.05). (4) Within the limitations of this retrospective study, the findings suggest that TMJ morphology and asymmetry could be associated with PD.
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Association between Temporomandibular Joint Disorder and Parkinson's Disease. Brain Sci 2021; 11:brainsci11060747. [PMID: 34200085 PMCID: PMC8229075 DOI: 10.3390/brainsci11060747] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2021] [Revised: 05/31/2021] [Accepted: 06/03/2021] [Indexed: 01/07/2023] Open
Abstract
This study performed two different analyses using a large set of population data from the Korean National Health Insurance Service Health Screening Cohort to evaluate the interactional association between temporomandibular disorder (TMD) and Parkinson’s disease (PD). Two nested case–control population-based studies were conducted on 514,866 participants. In Study I, 4455 participants with TMD were matched with 17,820 control participants, with a ratio of 1:4. In Study II, 6076 participants with PD were matched with 24,304 control participants, with a ratio of 1:4. Obesity, smoking, alcohol consumption, systolic, diastolic blood pressure, fasting blood glucose level, and total cholesterol were adjusted. The adjusted odds ratio (OR) for TMD was 1.43 (95% confidence interval (CI) = 1.02–2.00) in PD patients compared to non-PD patients in Study I (p < 0.001). The adjusted OR for PD was 1.56 (95% CI = 1.13–2.15) in TMD patients compared to non-TMD patients in Study II (p = 0.007). This study demonstrated that patients with TMD have a significantly higher risk of developing PD and, conversely, those with PD have a significantly higher risk of developing TMD.
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Moreira LS, Elias LA, Germer CM, Palomari ET. Reliable measurement of incisal bite force for understanding the control of masticatory muscles. Arch Oral Biol 2020; 112:104683. [PMID: 32120053 DOI: 10.1016/j.archoralbio.2020.104683] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2019] [Revised: 01/12/2020] [Accepted: 02/17/2020] [Indexed: 11/16/2022]
Abstract
OBJECTIVE In the present study, we aimed at evaluating the steadiness of incisal bite force during isometric contractions of masticatory muscles. DESIGN Two separate experiments were carried out in 11 healthy young women. A first experiment was performed to test the reliability of our protocol for measurement of incisal bite force steadiness. The second experiment aimed to evaluate the steadiness of incisal bite force at four submaximal (i.e., percentage of maximum voluntary contraction, MVC) levels (5 %MVC, 10 %MVC, 15 %MVC, and 20 %MVC), along with the bilateral myoelectric activity of two masticatory muscles (temporalis and masseter). RESULTS The results from the first experiment showed that our protocol is substantially reliable (intraclass correlation coefficient, ICC > 0.80) for estimating force variability and moderate reliable (0.60 < ICC < 0.80) for estimating spectral properties of force signals. In the second experiment, we found that force standard deviation (SD) increased proportionally to the power of mean force, and coefficient of variation (CoV) was higher at low-intensity contractions and maintained at an approximately constant level for high-intensity contractions. The force-EMG relationships were linear for both muscles at the contraction intensities evaluated in the study (5 %MVC to 20 %MVC), and the median frequency did not change with contraction intensity. CONCLUSION Therefore, we presented a reliable method to estimate the incisal bite force, along with additional data on force control and myoelectric activity of jaw elevator muscles during isometric steady contractions.
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Affiliation(s)
- Luciana S Moreira
- Cellular and Structural Biology Graduate Program, Institute of Biology, University of Campinas, Campinas, SP, Brazil; EMG, Motor Control, and Experimental Electrothermotherapy Laboratory, Department of Structural and Functional Biology, Institute of Biology, University of Campinas, Campinas, SP, Brazil; Neural Engineering Research Laboratory, Department of Biomedical Engineering, School of Electrical and Computer Engineering, University of Campinas, Campinas, SP, Brazil.
| | - Leonardo A Elias
- Neural Engineering Research Laboratory, Department of Biomedical Engineering, School of Electrical and Computer Engineering, University of Campinas, Campinas, SP, Brazil; Center for Biomedical Engineering, University of Campinas, Campinas, SP, Brazil
| | - Carina M Germer
- Neural Engineering Research Laboratory, Department of Biomedical Engineering, School of Electrical and Computer Engineering, University of Campinas, Campinas, SP, Brazil
| | - Evanisi T Palomari
- Cellular and Structural Biology Graduate Program, Institute of Biology, University of Campinas, Campinas, SP, Brazil; EMG, Motor Control, and Experimental Electrothermotherapy Laboratory, Department of Structural and Functional Biology, Institute of Biology, University of Campinas, Campinas, SP, Brazil
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Yilmaz G, Laine CM, Tinastepe N, Özyurt MG, Türker KS. Periodontal mechanoreceptors and bruxism at low bite forces. Arch Oral Biol 2018; 98:87-91. [PMID: 30468992 DOI: 10.1016/j.archoralbio.2018.11.011] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2018] [Revised: 10/09/2018] [Accepted: 11/10/2018] [Indexed: 11/25/2022]
Abstract
OBJECTIVE In this study, we examined if 6-9 Hz jaw tremor, an indirect indicator of Periodontal Mechanoreceptor (PMR) activity, is different in bruxists compared to healthy participants during production of a low-level constant bite force. METHODS Bite force and surface EMG from the masseter muscle were recorded simultaneously as participants (13 patients, 15 controls) held a force transducer between the upper and lower incisors very gently. RESULTS Tremor in 6-9 Hz band for bruxists was greater on average compared to controls, but the difference was not significant, both for force recordings and EMG activity. CONCLUSIONS The low effect sizes measured with the current protocol contrast highly with those of our previous study, where larger, dynamic bite forces were used, and where jaw tremor was markedly different in bruxists compared with controls. SIGNIFICANCE We have now gained important insight into the conditions under which abnormal jaw tremor can be elicited in bruxism. From a scientific standpoint, this is critical for understanding the 'abnormality' of PMR feedback in bruxism. From a clinical perspective, our results represent progress towards the development of an optimal protocol in which jaw tremor can serve as a biological marker of bruxism.
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Affiliation(s)
- Gizem Yilmaz
- Koç University School of Medicine, Istanbul, Turkey
| | - Christopher M Laine
- Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, CA, United States
| | - Neslihan Tinastepe
- Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, CA, United States
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Jalaleddini K, Nagamori A, Laine CM, Golkar MA, Kearney RE, Valero-Cuevas FJ. Physiological tremor increases when skeletal muscle is shortened: implications for fusimotor control. J Physiol 2017; 595:7331-7346. [PMID: 29023731 DOI: 10.1113/jp274899] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2017] [Accepted: 09/25/2017] [Indexed: 01/11/2023] Open
Abstract
KEY POINTS In tonic, isometric, plantarflexion contractions, physiological tremor increases as the ankle joint becomes plantarflexed. Modulation of physiological tremor as a function of muscle stretch differs from that of the stretch reflex amplitude. Amplitude of physiological tremor may be altered as a function of reflex pathway gains. Healthy humans likely increase their γ-static fusimotor drive when muscles shorten. Quantification of physiological tremor by manipulation of joint angle may be a useful experimental probe of afferent gains and/or the integrity of automatic fusimotor control. ABSTRACT The involuntary force fluctuations associated with physiological (as distinct from pathological) tremor are an unavoidable component of human motor control. While the origins of physiological tremor are known to depend on muscle afferentation, it is possible that the mechanical properties of muscle-tendon systems also affect its generation, amplification and maintenance. In this paper, we investigated the dependence of physiological tremor on muscle length in healthy individuals. We measured physiological tremor during tonic, isometric plantarflexion torque at 30% of maximum at three ankle angles. The amplitude of physiological tremor increased as calf muscles shortened in contrast to the stretch reflex whose amplitude decreases as muscle shortens. We used a published closed-loop simulation model of afferented muscle to explore the mechanisms responsible for this behaviour. We demonstrate that changing muscle lengths does not suffice to explain our experimental findings. Rather, the model consistently required the modulation of γ-static fusimotor drive to produce increases in physiological tremor with muscle shortening - while successfully replicating the concomitant reduction in stretch reflex amplitude. This need to control γ-static fusimotor drive explicitly as a function of muscle length has important implications. First, it permits the amplitudes of physiological tremor and stretch reflex to be decoupled. Second, it postulates neuromechanical interactions that require length-dependent γ drive modulation to be independent from α drive to the parent muscle. Lastly, it suggests that physiological tremor can be used as a simple, non-invasive measure of the afferent mechanisms underlying healthy motor function, and their disruption in neurological conditions.
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Affiliation(s)
- Kian Jalaleddini
- Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, CA, USA
| | - Akira Nagamori
- Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, CA, USA
| | - Christopher M Laine
- Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, CA, USA
| | - Mahsa A Golkar
- Department of Biomedical Engineering, McGill University, Montréal, QC, Canada
| | - Robert E Kearney
- Department of Biomedical Engineering, McGill University, Montréal, QC, Canada
| | - Francisco J Valero-Cuevas
- Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, CA, USA.,Department of Biomedical Engineering, University of Southern California, Los Angeles, CA, USA
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Laine CM, Nagamori A, Valero-Cuevas FJ. The Dynamics of Voluntary Force Production in Afferented Muscle Influence Involuntary Tremor. Front Comput Neurosci 2016; 10:86. [PMID: 27594832 PMCID: PMC4990560 DOI: 10.3389/fncom.2016.00086] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2016] [Accepted: 08/02/2016] [Indexed: 11/28/2022] Open
Abstract
Voluntary control of force is always marked by some degree of error and unsteadiness. Both neural and mechanical factors contribute to these fluctuations, but how they interact to produce them is poorly understood. In this study, we identify and characterize a previously undescribed neuromechanical interaction where the dynamics of voluntary force production suffice to generate involuntary tremor. Specifically, participants were asked to produce isometric force with the index finger and use visual feedback to track a sinusoidal target spanning 5-9% of each individual's maximal voluntary force level. Force fluctuations and EMG activity over the flexor digitorum superficialis (FDS) muscle were recorded and their frequency content was analyzed as a function of target phase. Force variability in either the 1-5 or 6-15 Hz frequency ranges tended to be largest at the peaks and valleys of the target sinusoid. In those same periods, FDS EMG activity was synchronized with force fluctuations. We then constructed a physiologically-realistic computer simulation in which a muscle-tendon complex was set inside of a feedback-driven control loop. Surprisingly, the model sufficed to produce phase-dependent modulation of tremor similar to that observed in humans. Further, the gain of afferent feedback from muscle spindles was critical for appropriately amplifying and shaping this tremor. We suggest that the experimentally-induced tremor may represent the response of a viscoelastic muscle-tendon system to dynamic drive, and therefore does not fall into known categories of tremor generation, such as tremorogenic descending drive, stretch-reflex loop oscillations, motor unit behavior, or mechanical resonance. Our findings motivate future efforts to understand tremor from a perspective that considers neuromechanical coupling within the context of closed-loop control. The strategy of combining experimental recordings with physiologically-sound simulations will enable thorough exploration of neural and mechanical contributions to force control in health and disease.
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Affiliation(s)
- Christopher M. Laine
- Department of Biomedical Engineering, University of Southern CaliforniaLos Angeles, CA, USA
- Division of Biokinesiology and Physical Therapy, University of Southern CaliforniaLos Angeles, CA, USA
| | - Akira Nagamori
- Division of Biokinesiology and Physical Therapy, University of Southern CaliforniaLos Angeles, CA, USA
| | - Francisco J. Valero-Cuevas
- Department of Biomedical Engineering, University of Southern CaliforniaLos Angeles, CA, USA
- Division of Biokinesiology and Physical Therapy, University of Southern CaliforniaLos Angeles, CA, USA
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