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Murtola T, Richards C. The impact of age-related increase in passive muscle stiffness on simulated upper limb reaching. ROYAL SOCIETY OPEN SCIENCE 2023; 10:221453. [PMID: 36778951 PMCID: PMC9905985 DOI: 10.1098/rsos.221453] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/09/2022] [Accepted: 01/18/2023] [Indexed: 06/18/2023]
Abstract
Ageing changes the musculoskeletal and neural systems, potentially affecting a person's ability to perform daily living activities. One of these changes is increased passive stiffness of muscles, but its contribution to performance is difficult to separate experimentally from other ageing effects such as loss of muscle strength or cognitive function. A computational upper limb model was used to study the effects of increasing passive muscle stiffness on reaching performance across the model's workspace (all points reachable with a given model geometry). The simulations indicated that increased muscle stiffness alone caused deterioration of reaching accuracy, starting from the edges of the workspace. Re-tuning the model's control parameters to match the ageing muscle properties does not fully reverse ageing effects but can improve accuracy in selected regions of the workspace. The results suggest that age-related muscle stiffening, isolated from other ageing effects, impairs reaching performance. The model also exhibited oscillatory instability in a few simulations when the controller was tuned to the presence of passive muscle stiffness. This instability is not observed in humans, implying the presence of natural stabilizing strategies, thus pointing to the adaptive capacity of neural control systems as a potential area of future investigation in age-related muscle stiffening.
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Affiliation(s)
- Tiina Murtola
- Department of Comparative Biomedical Sciences, Royal Veterinary College, London, UK
| | - Christopher Richards
- Department of Comparative Biomedical Sciences, Royal Veterinary College, London, UK
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Loubrie S, Trotier A, Ribot E, Massot P, Lefrançois W, Thiaudière E, Dallaudière B, Miraux S, Bourdel-Marchasson I. New setup for multi-parametric MRI in young and old rat gastrocnemius at 4.7 and 7 T during muscle stimulation. NMR IN BIOMEDICINE 2022; 35:e4620. [PMID: 34585794 DOI: 10.1002/nbm.4620] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2020] [Revised: 08/27/2021] [Accepted: 08/30/2021] [Indexed: 06/13/2023]
Abstract
T1 and T2 relaxation times combined with 31 P spectroscopy have been proven efficient for muscular disease characterization as well as for pre- and post-muscle stimulation measurements. Even though 31 P spectroscopy can already be performed during muscle exercise, no method for T1 and T2 measurement enables this possibility. In this project, a complete setup and protocol for multi-parametrical MRI of the rat gastrocnemius before, during and after muscle stimulation at 4.7 and 7 T is presented. The setup is fully MRI compatible and is composed of a cradle, an electro-stimulator and an electronic card in order to synchronize MRI sequences with muscle stimulation. A 2D triggered radial-encoded Look-Locker sequence was developed, and enabled T1 measurements in less than 2 min on stimulated muscle. Also, a multi-slice multi-echo sequence was adapted and synchronized for T2 measurements as well as 31 P spectroscopy acquisitions in less than 4 min in both cases on stimulated muscle. Methods were validated on young rats using different stimulation paradigms. Then they were applied on older rats to compare quantification results, using the different stimulation paradigms, and allowed observation of metabolic changes related to aging with good reproducibility. The robustness of the whole setup shows wide application opportunities.
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Affiliation(s)
- Stéphane Loubrie
- Centre de Résonance Magnétique des Systèmes Biologiques (CRMSB)-UMR 5536 CNRS/Université de Bordeaux, Bordeaux, France
| | - Aurelien Trotier
- Centre de Résonance Magnétique des Systèmes Biologiques (CRMSB)-UMR 5536 CNRS/Université de Bordeaux, Bordeaux, France
| | - Emeline Ribot
- Centre de Résonance Magnétique des Systèmes Biologiques (CRMSB)-UMR 5536 CNRS/Université de Bordeaux, Bordeaux, France
| | - Philippe Massot
- Centre de Résonance Magnétique des Systèmes Biologiques (CRMSB)-UMR 5536 CNRS/Université de Bordeaux, Bordeaux, France
| | - William Lefrançois
- Centre de Résonance Magnétique des Systèmes Biologiques (CRMSB)-UMR 5536 CNRS/Université de Bordeaux, Bordeaux, France
| | - Eric Thiaudière
- Centre de Résonance Magnétique des Systèmes Biologiques (CRMSB)-UMR 5536 CNRS/Université de Bordeaux, Bordeaux, France
| | - Benjamin Dallaudière
- Centre de Résonance Magnétique des Systèmes Biologiques (CRMSB)-UMR 5536 CNRS/Université de Bordeaux, Bordeaux, France
- Centre d'Imagerie Ostéo-articulaire, Clinique du Sport de Bordeaux-Mérignac, Mérignac, France
| | - Sylvain Miraux
- Centre de Résonance Magnétique des Systèmes Biologiques (CRMSB)-UMR 5536 CNRS/Université de Bordeaux, Bordeaux, France
| | - Isabelle Bourdel-Marchasson
- Centre de Résonance Magnétique des Systèmes Biologiques (CRMSB)-UMR 5536 CNRS/Université de Bordeaux, Bordeaux, France
- Pôle de gérontologie clinique, CHU de Bordeaux, Bordeaux, France
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Combinational spectral band activation complexity: Uncovering hidden neuromuscular firing dynamics in EMG. Biomed Signal Process Control 2021. [DOI: 10.1016/j.bspc.2021.102891] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Afonso J, Rocha-Rodrigues S, Clemente FM, Aquino M, Nikolaidis PT, Sarmento H, Fílter A, Olivares-Jabalera J, Ramirez-Campillo R. The Hamstrings: Anatomic and Physiologic Variations and Their Potential Relationships With Injury Risk. Front Physiol 2021; 12:694604. [PMID: 34305648 PMCID: PMC8294189 DOI: 10.3389/fphys.2021.694604] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2021] [Accepted: 06/16/2021] [Indexed: 01/11/2023] Open
Abstract
The incidence and recurrence of hamstrings injuries are very high in sports, posing elevated performance and financial-related costs. Attempts to identify the risk factors involved in predicting vulnerability to hamstrings injury is important for designing exercise-based programs that aim to mitigate the rate and severity of hamstrings injuries and improve rehabilitation strategies. However, research has shown that non-modifiable risk factors may play a greater role than modifiable risk factors. Recognizing non-modifiable risk factors and understanding their implications will afford the prescription of better suited exercise programs, i.e., that are more respectful of the individual characteristics. In a nutshell, non-modifiable risk factors can still be acted upon, even if indirectly. In this context, an underexplored topic is how intra and inter- individual anatomic and physiologic variations in hamstrings (e.g., muscle bellies, fiber types, tendon length, aponeurosis width, attachment sites, sex- and age-related differences) concur to alter hamstrings injuries risk. Some anatomic and physiologic variations may be modifiable through exercise interventions (e.g., cross-sectional area), while others may not (e.g., supernumerary muscle bellies). This apparent dichotomy may hide a greater complexity, i.e., there may be risk factors that are partially modifiable. Therefore, we explored the available information on the anatomic variations of the hamstrings, providing a deeper insight into the individual risk factors for hamstrings injuries and contributing with better knowledge and potential applications toward a more individualized exercise prescription.
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Affiliation(s)
- José Afonso
- Centre for Research, Education, Innovation and Intervention in Sport, Faculty of Sport of the University of Porto, Porto, Portugal
| | - Sílvia Rocha-Rodrigues
- Escola Superior de Desporto e Lazer, Instituto Politécnico de Viana do Castelo, Viana do Castelo, Portugal
- Research Centre in Sports Sciences, Health Sciences and Human Development, Vila Real, Portugal
- Tumor & Microenvironment Interactions Group, Instituto de Investigação e Inovação em Saúde, Porto, Portugal
| | - Filipe M. Clemente
- Escola Superior de Desporto e Lazer, Instituto Politécnico de Viana do Castelo, Viana do Castelo, Portugal
- Instituto de Telecomunicações, Delegação da Covilhã, Covilhã, Portugal
| | - Michele Aquino
- Department of Health and Sport Sciences, Adelphi University, New York, NY, United States
| | | | - Hugo Sarmento
- Research Unit for Sport and Physical Activity, Faculty of Sport Sciences and Physical Education, University of Coimbra, Coimbra, Portugal
| | - Alberto Fílter
- FSI Sport Research Lab, Football Science Institute, Granada, Spain
- Research Group Physical Activity, Health and Sport CTS-948, University of Pablo de Olavide, Seville, Spain
| | - Jesús Olivares-Jabalera
- FSI Sport Research Lab, Football Science Institute, Granada, Spain
- Sport and Health University Research Institute, Department of Physical and Sports Education, University of Granada, Granada, Spain
| | - Rodrigo Ramirez-Campillo
- Department of Physical Activity Sciences, Universidad de Los Lagos, Santiago, Chile
- Centro de Investigación en Fisiología del Ejercicio, Facultad de Ciencias, Universidad Mayor, Santiago, Chile
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Green B, Bourne MN, van Dyk N, Pizzari T. Recalibrating the risk of hamstring strain injury (HSI): A 2020 systematic review and meta-analysis of risk factors for index and recurrent hamstring strain injury in sport. Br J Sports Med 2020; 54:1081-1088. [PMID: 32299793 DOI: 10.1136/bjsports-2019-100983] [Citation(s) in RCA: 128] [Impact Index Per Article: 32.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/28/2020] [Indexed: 01/26/2023]
Abstract
OBJECTIVE To systematically review risk factors for hamstring strain injury (HSI). DESIGN Systematic review update. DATA SOURCES Database searches: (1) inception to 2011 (original), and (2) 2011 to December 2018 (update). Citation tracking, manual reference and ahead of press searches. ELIGIBILITY CRITERIA FOR SELECTING STUDIES Studies presenting prospective data evaluating factors associated with the risk of index and/or recurrent HSI. METHOD Search result screening and risk of bias assessment. A best evidence synthesis for each factor and meta-analysis, where possible, to determine the association with risk of HSI. RESULTS The 78 studies captured 8,319 total HSIs, including 967 recurrences, in 71,324 athletes. Older age (standardised mean difference=1.6, p=0.002), any history of HSI (risk ratio (RR)=2.7, p<0.001), a recent HSI (RR=4.8, p<0.001), previous anterior cruciate ligament (ACL) injury (RR=1.7, p=0.002) and previous calf strain injury (RR=1.5, p<0.001) were significant risk factors for HSI. From the best evidence synthesis, factors relating to sports performance and match play, running and hamstring strength were most consistently associated with HSI risk. The risk of recurrent HSI is best evaluated using clinical data and not the MRI characteristics of the index injury. SUMMARY/CONCLUSION Older age and a history of HSI are the strongest risk factors for HSI. Future research may be directed towards exploring the interaction of risk factors and how these relationships fluctuate over time given the occurrence of index and recurrent HSI in sport is multifactorial.
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Affiliation(s)
- Brady Green
- La Trobe Sport and Exercise Medicine Research Centre, La Trobe University, Melbourne, Victoria, Australia
| | - Matthew N Bourne
- La Trobe Sport and Exercise Medicine Research Centre, La Trobe University, Melbourne, Victoria, Australia.,School of Allied Health Sciences, Griffith University, Gold Coast Campus, Queensland, Australia
| | - Nicol van Dyk
- High Performance Unit, Irish Rugby Football Union, Dublin, Ireland
| | - Tania Pizzari
- La Trobe Sport and Exercise Medicine Research Centre, La Trobe University, Melbourne, Victoria, Australia
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Kirk EA, Gilmore KJ, Stashuk DW, Doherty TJ, Rice CL. Human motor unit characteristics of the superior trapezius muscle with age-related comparisons. J Neurophysiol 2019; 122:823-832. [PMID: 31242057 DOI: 10.1152/jn.00138.2019] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Current understanding of human motor unit (MU) control and aging is mostly derived from hand and limb muscles that have spinal motor neuron innervations. The aim here was to characterize and test whether a muscle with a shared innervation supply from brainstem and spinal MU populations would demonstrate similar age-related adaptations as those reported for other muscles. In humans, the superior trapezius (ST) muscle acts to elevate and stabilize the scapula and has primary efferent supply from the spinal accessory nerve (cranial nerve XI) located in the brainstem. We compared electrophysiological properties obtained from intramuscular and surface recordings between 10 young (22-33 yr) and 10 old (77-88 yr) men at a range of voluntary isometric contraction intensities (from 15 to 100% of maximal efforts). The old group was 41% weaker with 43% lower MU discharge frequencies compared with the young (47.2 ± 9.6 Hz young and 26.7 ± 5.8 Hz old, P < 0.05) during maximal efforts. There was no difference in MU number estimation between age groups (228 ± 105 young and 209 ± 89 old, P = 0.33). Furthermore, there were no differences in needle detected near fiber (NF) stability parameters of jitter or jiggle. The old group had lower amplitude and smaller area of the stimulated compound muscle action potential and smaller NF MU potential area with higher NF counts. Thus, despite age-related ST weakness and lower MU discharge rates, there was minimal evidence of MU loss or compensatory reinnervation.NEW & NOTEWORTHY The human superior trapezius (ST) has shared spinal and brainstem motor neuron innervation providing a unique model to explore the impact of aging on motor unit (MU) properties. Although the ST showed higher MU discharge rates compared with most spinally innervated muscles, voluntary strength and mean MU rates were lower in old compared with young at all contraction intensities. There was no age-related difference in MU number estimates with minimal electrophysiological evidence of collateral reinnervation.
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Affiliation(s)
- Eric A Kirk
- School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, Ontario, Canada
| | - Kevin J Gilmore
- School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, Ontario, Canada
| | - Daniel W Stashuk
- Department of Systems Design Engineering, University of Waterloo, Ontario, Canada
| | - Timothy J Doherty
- Department of Clinical Neurological Sciences, The University of Western Ontario, London, Ontario, Canada.,Department of Physical Medicine and Rehabilitation, The University of Western Ontario, London, Ontario, Canada
| | - Charles L Rice
- School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, Ontario, Canada.,Department of Anatomy and Cell Biology, The University of Western Ontario, London, Ontario, Canada
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MacDonell CW, Gardiner PF. Mechanisms and functional implications of motoneuron adaptations to increased physical activity. Appl Physiol Nutr Metab 2018; 43:1186-1193. [DOI: 10.1139/apnm-2018-0185] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Motoneurons demonstrate adaptations in their physiological properties to alterations in chronic activity levels. The most consistent change that appears to result from endurance-type exercise training is the reduced excitatory current required to initiate and maintain rhythmic firing. While the precise mechanisms through which these neurons adapt to activity are currently unknown, evidence exists that adaptation may involve alterations in the expression of genes that code for membrane receptors, which can influence the responses of neurons to transmitters during activation. The influence of these adaptations may also extend to the resting condition, where ambient levels of neuroactive substances may influence ion conductances at rest, and thus result in the activation or inhibition of specific ion conductances that underlie the measurements of increased excitability that have been reported for motoneurons in the anesthetised state. We have applied motoneuron excitability and muscle unit contractile changes with endurance training to a mathematical computerized model of motor unit recruitment (Heckman and Binder 1991; J. Neurophysiol. 65(4):952–967). The results from the modelling exercise demonstrate increased task efficiency at relative levels of effort during a submaximal contraction. The physiological impact that nerve and muscle adaptations have on the neuromuscular system during standardized tasks seem to fit with reported changes in motor unit behaviour in trained human subjects.
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Affiliation(s)
- Christopher W. MacDonell
- Spinal Cord Research Center, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, MB R3E 0J9, Canada
- Spinal Cord Research Center, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, MB R3E 0J9, Canada
| | - Phillip F. Gardiner
- Spinal Cord Research Center, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, MB R3E 0J9, Canada
- Spinal Cord Research Center, Rady Faculty of Health Sciences, University of Manitoba, Winnipeg, MB R3E 0J9, Canada
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8
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Kirk EA, Gilmore KJ, Rice CL. Neuromuscular changes of the aged human hamstrings. J Neurophysiol 2018; 120:480-488. [PMID: 29668388 DOI: 10.1152/jn.00794.2017] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Despite the life-long importance for posture and locomotion, neuromuscular properties of the hamstrings muscle have not been explored with adult aging. The purpose of this study was to assess and compare age-related effects on contractile function, spinal motor neuron output expressed as motor unit (MU) discharge rates in the hamstrings of 11 young (26 ± 4 yr) and 10 old (80 ± 5 yr) men. Maximal voluntary isometric contractions (MVC), stimulated contractile properties, and surface and intramuscular electromyography (EMG) from submaximal to MVC were recorded in the biceps femoris (BF) and semimembranosus-semitendinosus (SS) muscles. MVC torque was ~50% less in the old with both age groups attaining ≥93% mean voluntary activation. Evoked twitches in the old were ~50% lower in amplitude and >150% longer in duration compared with those in the young. At successive voluntary contractions of 25, 50, and 100% MVC, MU discharge rates were up to 45% lower in old, with no differences in relative submaximal surface EMG between age groups. Furthermore, the old had significantly lower MU discharge rates in the SS at all contraction intensities compared with the BF muscle. Men in their 8th to 10th decades of life demonstrate substantially lower strength and MU discharge rates in this functionally important large lower limb muscle group, with greater age-related effect on discharge rates in the medial hamstrings. These findings, compared with those in other muscles studied, highlight that the neuromuscular properties of limb muscles, and indeed within functionally similar portions of a muscle group, are not all affected equally by the aging process. NEW & NOTEWORTHY In the hamstrings, we found that both contractile function and motor unit discharge rates across the range of voluntary intensities were lower in the old. The differences in discharge rates due to age were greater in the medial hamstrings muscle group compared with the lateral hamstrings. Compared with previous studies, these results highlight that not all muscles are affected equally by aging and there may be compartmental differences within functionally similar muscles.
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Affiliation(s)
- Eric A Kirk
- Neuromuscular Laboratory, School of Kinesiology, The University of Western Ontario, London, Ontario , Canada
| | - Kevin J Gilmore
- Neuromuscular Laboratory, School of Kinesiology, The University of Western Ontario, London, Ontario , Canada
| | - Charles L Rice
- Neuromuscular Laboratory, School of Kinesiology, The University of Western Ontario, London, Ontario , Canada.,Department of Anatomy and Cell Biology, Schulich School of Medicine and Dentistry, The University of Western Ontario , London, Ontario , Canada.,The Canadian Centre for Activity and Ageing, The University of Western Ontario , London, Ontario , Canada
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Siddiqi A, Poosapadi Arjunan S, Kumar DK. Computational model to investigate the relative contributions of different neuromuscular properties of tibialis anterior on force generated during ankle dorsiflexion. Med Biol Eng Comput 2018; 56:1413-1423. [PMID: 29335929 DOI: 10.1007/s11517-018-1788-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2017] [Accepted: 01/06/2018] [Indexed: 10/18/2022]
Abstract
This study describes a new model of the force generated by tibialis anterior muscle with three new features: single-fiber action potential, twitch force, and pennation angle. This model was used to investigate the relative effects and interaction of ten age-associated neuromuscular parameters. Regression analysis (significance level of 0.05) between the neuromuscular properties and corresponding simulated force produced at the footplate was performed. Standardized slope coefficients were computed to rank the effect of the parameters. The results show that reduction in the average firing rate is the reason for the sharp decline in the force and other factors, such as number of muscle fibers, specific force, pennation angle, and innervation ratio. The fast fiber ratio affects the simulated force through two significant interactions. This study has ranked the individual contributions of the neuromuscular factors to muscle strength decline of the TA and identified firing rate decline as the biggest cause followed by decrease in muscle fiber number and specific force. The strategy for strength preservation for the elderly should focus on improving firing rate. Graphical abstract Neuromuscular properties of Tibialis Anterior on force generated during ankle dorsiflexion.
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Affiliation(s)
- Ariba Siddiqi
- Biosignals Laboratory, School of Engineering, RMIT University, GPO Box 2476, Melbourne, VIC, Australia
| | - Sridhar Poosapadi Arjunan
- Biosignals Laboratory, School of Engineering, RMIT University, GPO Box 2476, Melbourne, VIC, Australia.
| | - Dinesh Kant Kumar
- Biosignals Laboratory, School of Engineering, RMIT University, GPO Box 2476, Melbourne, VIC, Australia
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Cowling BL, Harwood B, Copithorne DB, Rice CL. Rate modulation of human anconeus motor units during high-intensity dynamic elbow extensions. J Appl Physiol (1985) 2016; 121:475-82. [PMID: 27283910 DOI: 10.1152/japplphysiol.00131.2016] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2016] [Accepted: 06/06/2016] [Indexed: 11/22/2022] Open
Abstract
Investigations of high-intensity isometric fatiguing protocols report decreases in motor unit firing rates (MUFRs), but little is known regarding changes in MUFRs following fatigue induced by high-intensity dynamic contractions. Our purpose was to evaluate MUFRs of the anconeus (an accessory elbow extensor) and elbow extension power production as a function of time to task failure (TTF) during high-velocity fatiguing concentric contractions against a moderately heavy resistance. Fine-wire intramuscular electrode pairs were inserted into the anconeus to record MUs in 12 male participants (25 ± 3 yr), over repeated sessions on separate days. MUs were tracked throughout a three-stage, varying load dynamic elbow extension protocol designed to extend the task duration for >1 min thereby inducing substantial fatigue. Mean MUFRs and peak power were calculated for three relative time ranges: 0-15% TTF (beginning), 45-60% TTF (middle) and 85-100% TTF (end). Mean duration of the overall fatigue protocol was ∼80 s. Following the protocol, isometric maximum voluntary contraction (MVC), highest velocity at 35% MVC load, and peak power decreased 37, 60, and 64% compared with baseline, respectively. Data from 20 anconeus MUs tracked successfully throughout the protocol indicated a reduction in MUFRs in relation to power loss from 36 Hz/160 W (0-15% TTF) to 28 Hz/97 W (45-60% TTF) to 23 Hz/43 W (85-100% TTF). During these high-intensity maximal effort concentric contractions, anconeus MUFRs decreased substantially (>35%). Although the absolute MUFRs were higher in the present study than those reported previously for other muscles during sustained high-intensity isometric tasks, the relative decrease in MUFRs was similar between the two tasks.
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Affiliation(s)
- Brianna L Cowling
- School of Kinesiology, The University of Western Ontario, London, Ontario, Canada; and
| | - Brad Harwood
- School of Kinesiology, The University of Western Ontario, London, Ontario, Canada; and
| | - David B Copithorne
- School of Kinesiology, The University of Western Ontario, London, Ontario, Canada; and
| | - Charles L Rice
- School of Kinesiology, The University of Western Ontario, London, Ontario, Canada; and Department of Anatomy and Cell Biology, The University of Western Ontario, London, Ontario, Canada
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PINCIVERO DANNYM. Older Adults Underestimate RPE and Knee Extensor Torque as Compared with Young Adults. Med Sci Sports Exerc 2011; 43:171-80. [DOI: 10.1249/mss.0b013e3181e91e0d] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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12
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Harwood B, Davidson AW, Rice CL. Motor unit discharge rates of the anconeus muscle during high-velocity elbow extensions. Exp Brain Res 2010; 208:103-13. [PMID: 21107544 DOI: 10.1007/s00221-010-2463-4] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2010] [Accepted: 10/10/2010] [Indexed: 10/18/2022]
Abstract
Motor unit recruitment and motor unit discharge rate (MUDR) have been widely studied in isometric conditions but minimally during velocity-dependent contractions. For isometric contractions, surface electromyography (EMG) activity of the elbow extensors plateaus at near maximal torques (Le Bozec et al. 1980; Le Bozec and Maton 1982). One study (Maton and Bouisset 1975) recorded single motor unit (MU) activity at maximal velocities; however, only the rate of the first interspike interval (ISI) was reported and likely was not representative of the average MUDR of the MU train. The purpose was to calculate average MUDRs of the anconeus during loaded velocity-dependent contractions from zero velocity (isometric) up to maximal velocity (V(max25)) through a large range of motion. A Biodex dynamometer was used to record elbow extension torque, position, and velocity. Single MU potentials were collected from the anconeus with intramuscular EMG, and surface EMG was sampled from the lateral head of the triceps brachii during maximal voluntary isometric contractions (MVCs) and velocity-dependent contractions loaded at 25% MVC over 120° range of motion at five target velocities (0, 25, 50, 75, 100%V(max25)). Elbow extension velocities ranged from 93 to 494°/s and average MUDR ranged from 11.8 Hz at 25%MVC to 39.0 Hz at 100%V(max25.) Overall average MUDRs increased as a function of velocity, although the root mean square of triceps brachii surface EMG plateaued at 50%V(max25). Piecewise regression analysis revealed two distinct linear ranges each described by a unique equation, suggesting that MUDRs of the anconeus enter a secondary range of firing, characterized by a steeper slope as velocity approaches maximum.
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Affiliation(s)
- B Harwood
- Canadian Centre for Activity and Aging, Faculty of Health Sciences, School of Kinesiology, The University of Western Ontario, London, ON N6A 3K7, Canada
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