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Pereira HM, Keenan KG, Hunter SK. Influence of visual feedback and cognitive challenge on the age-related changes in force steadiness. Exp Brain Res 2024; 242:1411-1419. [PMID: 38613669 DOI: 10.1007/s00221-024-06831-w] [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: 11/19/2023] [Accepted: 04/05/2024] [Indexed: 04/15/2024]
Abstract
Force steadiness can be influenced by visual feedback as well as presence of a cognitive tasks and potentially differs with age and sex. This study determined the impact of altered visual feedback on force steadiness in the presence of a difficult cognitive challenge in young and older men and women. Forty-nine young (19-30 yr; 25 women, 24 men) and 25 older (60-85 yr; 15 women; 10 men) performed low force (5% of maximum) static contractions with the elbow flexor muscles in the presence and absence of a cognitive challenge (counting backwards by 13) either with low or high visual feedback gain. The cognitive challenge reduced force steadiness (increased force fluctuation amplitude) particularly in women (cognitive challenge × sex: P < 0.05) and older individuals (cognitive challenge × age: P < 0.05). Force steadiness improved with high-gain visual feedback compared with low-gain visual feedback (P < 0.01) for all groups (all interactions: P > 0.05). Manipulation of visual feedback had no influence on the reduced force steadiness in presence of the cognitive challenge for all groups (all P > 0.05). These findings indicate that older individuals and women have greater risk of impaired motor performance of the upper extremity if steadiness is required during a low-force static contraction. Manipulation of visual feedback had minimal effects on the reduced force steadiness in presence of a difficult cognitive challenge.
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Affiliation(s)
- Hugo M Pereira
- Department of Health and Exercise Science, University of Oklahoma, Norman, OK, USA.
| | - Kevin G Keenan
- Joseph J. Zilber College of Public Health, University of Wisconsin-Milwaukee, Milwaukee, USA
| | - Sandra K Hunter
- Exercise Science Program, Department of Physical Therapy, Marquette University, Milwaukee, USA
- Athletic and Human Performance Research Center, Marquette University, Milwaukee, USA
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Cohen JW, Vieira TM, Ivanova TD, Garland SJ. Regional recruitment and differential behavior of motor units during postural control in older adults. J Neurophysiol 2023; 130:1321-1333. [PMID: 37877159 DOI: 10.1152/jn.00068.2023] [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: 02/13/2023] [Revised: 10/23/2023] [Accepted: 10/23/2023] [Indexed: 10/26/2023] Open
Abstract
Aging is associated with neuromuscular system changes that may have implications for the recruitment and firing behaviors of motor units (MUs). In previous studies, we observed that young adults recruit subpopulations of triceps surae MUs during tasks that involved leaning in five directions: common units that were active during different leaning directions and unique units that were active in only one leaning direction. Furthermore, the MU subpopulation firing behaviors [average firing rate (AFR), coefficient of variation (CoVISI), and intermittent firing] modulated with leaning direction. The purpose of this study was to examine whether older adults exhibited this regional recruitment of MUs and firing behaviors. Seventeen older adults (aged 74.8 ± 5.3 yr) stood on a force platform and maintained their center of pressure leaning in five directions. High-density surface electromyography recordings from the triceps surae were decomposed into single MU action potentials. A MU tracking analysis identified groups of MUs as being common or unique across the leaning directions. Although leaning in different directions did not affect the AFR and CoVISI of common units (P > 0.05), the unique units responded to the leaning directions by increasing AFR and CoVISI, albeit modestly (F = 18.51, P < 0.001). The unique units increased their intermittency with forward leaning (F = 9.22, P = 0.003). The mediolateral barycenter positions of MU activity in both subpopulations were found in similar locations for all leaning directions (P > 0.05). These neuromuscular changes may contribute to the reduced balance performance seen in older adults.NEW & NOTEWORTHY In this study, we observed differences in motor unit recruitment and firing behaviors of distinct subpopulations of motor units in the older adult triceps surae muscle from those observed in the young adult. Our results suggest that the older adult central nervous system may partially lose the ability to regionally recruit and differentially control motor units. This finding may be an underlying cause of balance difficulties in older adults during directionally challenging leaning tasks.
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Affiliation(s)
- Joshua W Cohen
- School of Kinesiology, Western University, London, Ontario, Canada
- Faculty of Health Sciences, School of Physical Therapy, Western University, London, Ontario, Canada
| | - Taian M Vieira
- Department of Physiology and Pharmacology, Schulich School of Medicine & Dentistry, Western University, London, Ontario, Canada
| | - Tanya D Ivanova
- Faculty of Health Sciences, School of Physical Therapy, Western University, London, Ontario, Canada
| | - S Jayne Garland
- Faculty of Health Sciences, School of Physical Therapy, Western University, London, Ontario, Canada
- Collaborative Specialization in Musculoskeletal Health Research, Bone and Joint Institute, Western University, London, Ontario, Canada
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Pethick J, Taylor MJD, Harridge SDR. Ageing and skeletal muscle force control: current perspectives and future directions. Scand J Med Sci Sports 2022; 32:1430-1443. [PMID: 35815914 PMCID: PMC9541459 DOI: 10.1111/sms.14207] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2022] [Revised: 05/23/2022] [Accepted: 06/22/2022] [Indexed: 11/29/2022]
Abstract
During voluntary muscle contractions, force output is characterized by constant inherent fluctuations, which can be quantified either according to their magnitude or temporal structure, that is, complexity. The presence of such fluctuations when targeting a set force indicates that control of force is not perfectly accurate, which can have significant implications for task performance. Compared to young adults, older adults demonstrate a greater magnitude and lower complexity in force fluctuations, indicative of decreased steadiness, and adaptability of force output, respectively. The nature of this loss‐of‐force control depends not only on the age of the individual but also on the muscle group performing the task, the intensity and type of contraction and whether the task is performed with additional cognitive load. Importantly, this age‐associated loss‐of‐force control is correlated with decreased performance in a range of activities of daily living and is speculated to be of greater importance for functional capacity than age‐associated decreases in maximal strength. Fortunately, there is evidence that acute physical activity interventions can reverse the loss‐of‐force control in older individuals, though whether this translates to improved functional performance and whether lifelong physical activity can protect against the changes have yet to be established. A number of mechanisms, related to both motor unit properties and the behavior of motor unit populations, have been proposed for the age‐associated changes in force fluctuations. It is likely, though, that age‐associated changes in force control are related to increased common fluctuations in the discharge times of motor units.
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Affiliation(s)
- Jamie Pethick
- School of Sport, Rehabilitation and Exercise Sciences, University of Essex, Essex, UK
| | - Matthew J D Taylor
- School of Sport, Rehabilitation and Exercise Sciences, University of Essex, Essex, UK
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Hirono T, Ikezoe T, Taniguchi M, Yamagata M, Umehara J, Ichihashi N. Acute effects of ankle plantar flexor force-matching exercises on postural strategy during single leg standing in healthy adults. Gait Posture 2022; 92:428-434. [PMID: 34979429 DOI: 10.1016/j.gaitpost.2021.12.021] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/16/2020] [Revised: 12/23/2021] [Accepted: 12/28/2021] [Indexed: 02/02/2023]
Abstract
BACKGROUND Ankle plantar flexor force steadiness, assessed by measuring the fluctuation of the force around the submaximal target torque, has been associated with postural stability. RESEARCH QUESTION To investigate whether a force-matching exercise, where submaximal steady torque is maintained at the target torque, can modulate postural strategy immediately. METHODS Twenty-eight healthy young adults performed ankle plantar flexor force-matching exercises at target torques of 5%, 20%, and 50% of maximum voluntary contraction (MVC), in a randomized crossover trial. Participants with their ankle in a neutral position were instructed to maintain isometric contraction at each target torque, as measured by a dynamometer, for 20 s with 3 sets of 5 contractions. Before and after the force-matching exercises, the anterior-posterior velocities and standard deviation of the center of pressure (COP) on the stable platform and the tilt angle of the unstable platform during 20-seconds single-leg standing were measured. The velocities and standard deviations of the COP and tilt angle before and after the exercises were compared using paired t-tests. RESULTS The tilt angle velocity of an unstable platform significantly decreased after the force-matching exercise at a target torque of 5% MVC (p = 0.029), whereas it was unchanged after the exercises at target torques of 20% and 50% MVC. The standard deviations of the tilt angle of unstable platform test did not change significantly after any exercise. Furthermore, no significant differences were observed in the COP velocities or standard deviations on the stable platform test after any exercise. SIGNIFICANCE Our findings suggest that repeated exertion training at low-intensity contractions can affect postural stability in an unstable condition. Particularly, force-matching exercise at very low-intensity torque, such as 5% of MVC, may be an effective method to improve postural control in the unstable condition, but not in a stable condition.
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Affiliation(s)
- Tetsuya Hirono
- Human Health Sciences, Graduate School of Medicine, Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan; Research Fellow of the Japan Society for the Promotion of Science, 5-3-1 Kojimachi, Chiyoda-ku, Tokyo 102-0083, Japan; School of Health and Sport Sciences, Chukyo University, 101 Tokodachi, Kaizu-cho, Toyota, Aichi 470-0393 Japan.
| | - Tome Ikezoe
- Human Health Sciences, Graduate School of Medicine, Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan; Department of Physical Medicine and Rehabilitation, Kansai Medical University, 2-5-1 Shin-machi, Hirakata, Osaka 573-1010, Japan
| | - Masashi Taniguchi
- Human Health Sciences, Graduate School of Medicine, Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan
| | - Momoko Yamagata
- Human Health Sciences, Graduate School of Medicine, Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan; Research Fellow of the Japan Society for the Promotion of Science, 5-3-1 Kojimachi, Chiyoda-ku, Tokyo 102-0083, Japan; Department of Human Development, Graduate School of Human Development and Environment, Kobe University, 3-11 Tsurukabuto, Nada-ku, Kobe, Hyogo 657-0011, Japan
| | - Jun Umehara
- Human Health Sciences, Graduate School of Medicine, Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan; Research Fellow of the Japan Society for the Promotion of Science, 5-3-1 Kojimachi, Chiyoda-ku, Tokyo 102-0083, Japan; Center for Information and Neural Networks (CiNet), National Institute of Information and Communications Technology, 1-4, Yamadaoka, Suita, Osaka 565-0871, Japan
| | - Noriaki Ichihashi
- Human Health Sciences, Graduate School of Medicine, Kyoto University, 53 Shogoin-Kawahara-cho, Sakyo-ku, Kyoto 606-8507, Japan
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Enoka RM, Farina D. Force Steadiness: From Motor Units to Voluntary Actions. Physiology (Bethesda) 2021; 36:114-130. [DOI: 10.1152/physiol.00027.2020] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Voluntary actions are controlled by the synaptic inputs that are shared by pools of spinal motor neurons. The slow common oscillations in the discharge times of motor units due to these synaptic inputs are strongly correlated with the fluctuations in force during submaximal isometric contractions (force steadiness) and moderately associated with performance scores on some tests of motor function. However, there are key gaps in knowledge that limit the interpretation of differences in force steadiness.
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Affiliation(s)
- Roger M. Enoka
- Department of Integrative Physiology, University of Colorado Boulder, Colorado
| | - Dario Farina
- Department of Bioengineering, Faculty of Engineering, Imperial College London, London, United Kingdom
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Hirono T, Ikezoe T, Taniguchi M, Yamagata M, Miyakoshi K, Umehara J, Ichihashi N. Relationship between ankle plantar flexor force steadiness and postural stability on stable and unstable platforms. Eur J Appl Physiol 2020; 120:1075-1082. [DOI: 10.1007/s00421-020-04346-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2019] [Accepted: 03/10/2020] [Indexed: 01/06/2023]
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Davis LA, Allen SP, Hamilton LD, Grabowski AM, Enoka RM. Differences in postural sway among healthy adults are associated with the ability to perform steady contractions with leg muscles. Exp Brain Res 2020; 238:487-497. [PMID: 31960103 DOI: 10.1007/s00221-019-05719-4] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2019] [Accepted: 12/30/2019] [Indexed: 12/13/2022]
Abstract
Upright standing involves small displacements of the center of mass about the base of support. These displacements are often quantified by measuring various kinematic features of the center-of-pressure trajectory. The plantar flexors have often been identified as the key muscles for the control of these displacements; however, studies have suggested that the hip abductor and adductors may also be important. The purpose of our study was to determine the association between the force capabilities of selected leg muscles and sway-area rate across four balance conditions in young (25 ± 4 years; 12/19 women) and older adults (71 ± 5 years; 5/19 women). Due to the marked overlap in sway-area rate between the two age groups, the data were collapsed, and individuals were assigned to groups of low- and high-sway area rates based on a k-medoid cluster analysis. The number of participants assigned to each group varied across balance conditions and a subset of older adults was always included in the low-sway group for each balance condition. The most consistent explanatory variable for the variance in sway-area rate was force control of the hip abductors and ankle dorsiflexors as indicated by the magnitude of the normalized force fluctuations (force steadiness) during a submaximal isometric contraction. The explanatory power of the regression models varied across conditions, thereby identifying specific balance conditions that should be examined further in future studies of postural control.
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Affiliation(s)
- Leah A Davis
- Department of Integrative Physiology, University of Colorado Boulder, Campus Box 354, Boulder, CO, 80309, USA.
| | - Stephen P Allen
- Department of Integrative Physiology, University of Colorado Boulder, Campus Box 354, Boulder, CO, 80309, USA
| | - Landon D Hamilton
- Center for Orthopedic Biomechanics, Ritchie School of Mechanical Engineering and Computer Science, University of Denver, 2155 E. Wesley Ave., Denver, CO, 80210, USA
| | - Alena M Grabowski
- Department of Integrative Physiology, University of Colorado Boulder, Campus Box 354, Boulder, CO, 80309, USA
| | - Roger M Enoka
- Department of Integrative Physiology, University of Colorado Boulder, Campus Box 354, Boulder, CO, 80309, 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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