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Steven Morrison - One of the best experts on this subject based on the ideXlab platform.
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Differences in postural Tremor dynamics with age and neurological disease
Experimental Brain Research, 2017Co-Authors: Steven Morrison, Karl M Newell, Justin J. KavanaghAbstract:The overlap of dominant Tremor frequencies and similarly amplified Tremor observed for Parkinson’s disease (PD) and essential Tremor (ET) means differentiating between these pathologies is often difficult. As Tremor exhibits non-linear properties, employing both linear and non-linear analyses may help distinguish between the Tremor dynamics of aging, PD and ET. This study was designed to examine postural Tremor in healthy older adults, PD and ET using standard linear and non-linear metrics. Hand and Finger postural Tremor was recorded in 15 healthy older adults (64 ± 6 years), 15 older individuals with PD (63 ± 6 years), and 10 persons with ET (68 ± 7 years). Linear measures of amplitude, frequency, and between-limb coupling (coherence) were performed. Non-linear measures of regularity (ApEn) and coupling (Cross-ApEn) were also used. Additionally, receiver operating characteristic analyses were performed for those measures that were significantly different between all groups. The results revealed that the linear measures only showed significant differences between the healthy adults and ET/PD persons, but no differences between the two neurological groups. Coherence showed higher bilateral coupling for ET but no differences in inter-limb coupling between PD and healthy subjects. However, ApEn values for Finger Tremor revealed significant differences between all groups, with Tremor for ET persons being more regular (lower ApEn) overall. Similarly, Cross-ApEn results also showed differences between all groups, with ET persons showing strongest inter-limb coupling followed by PD and elderly. Overall, our findings point to the diagnostic potential for non-linear measures of coupling and Tremor structure as biomarkers for discriminating between ET, PD and healthy persons.
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Differences in Multiple Segment Tremor Dynamics Between Young and Elderly Persons
2014Co-Authors: Steven Morrison, Peter Mills, Rod BarrettAbstract:Background. Physiological Tremor is an intrinsic and highly variable motor output that is sensitive to alteration in both neuromuscular function and/or changing task demands. Given that any Tremor increase can severely influence fine motor performance, there is a requirement to clarify what factors lead to increased Tremor. Identification of those factors that alter Tremor may be particularly pertinent for elderly persons, who often exhibit a decline in postural control and amplified Tremor. The aim of this study was to examine the effect of whole body posture (seated vs standing) on multiple segment Tremor and forearm electromyogram (EMG) activity of younger and older individuals. Methods. Fourteen older and 12 young participants performed a bilateral pointing task. Tremor data were collected using accelerometers attached to the forearm, hand, and Finger segments of each arm. Surface EMG data were also collected from the extensor digitorum muscle of each arm. Results. Although the pattern of Tremor was similar between age groups, older participants exhibited increased hand and Finger Tremor amplitude and increased EMG activity across all postural conditions. For older individuals, Tremor increases were greatest when the participant performed the task in a standing position. All age-related increases in hand and/or Finger Tremor were confined to increases in peak power between 8 Hz and 12 Hz. Conclusions. From a clinical perspective, these findings illustrate that using multiple segment Tremor analyses can provide additional insight into potential age-related Tremor differences. Additionally, the fact that postural position ha
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load induced changes in older individual s hand Finger Tremor are ameliorated with targeting
Journal of the Neurological Sciences, 2014Co-Authors: Justin J. Kavanagh, Karl M Newell, Troy J Cross, Steven MorrisonAbstract:Abstract The purpose of this study was to investigate hand–Finger Tremor dynamics when a load was applied to the Finger in a group of healthy older adults. Moreover, we sought to determine if projecting a representation of the subject's Finger Tremor on a target was capable of overcoming the effects of loading so that hand–Finger interactions returned to a state that was similar to normal Tremor. Eight healthy older males (67 ± 1 year) performed a postural pointing task, where Tremor was assessed using lightweight accelerometers attached to the hand and Finger. Tremor was then assessed when a laser pointer was attached to the Finger and switched off (the load), and then with the laser pointer attached and switched on pointing at targets of 40 mm and 20 mm in diameter. The main findings of this study were that 1) loading the Finger resulted in a reduction in Finger Tremor amplitude and increased Finger Tremor regularity, but no change in hand Tremor, 2) loading caused increased hand–Finger 8–12 Hz cross wavelet coherence and phase synchrony, and 3) pointing at different targets while the Finger was loaded resulted in an increase in Finger Tremor amplitude, and changes in inter-segmental coupling to the extent that hand–Finger dynamics reflected normal unloaded conditions. Overall, these results illustrate that the damping effects of limb loading can be offset, in part, by altering the accuracy demands of the task to make the pointing action more challenging.
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strength and coordination training are both effective in reducing the postural Tremor amplitude of older adults
Journal of Aging and Physical Activity, 2010Co-Authors: Justin W.l. Keogh, Steven Morrison, Rod BarrettAbstract:The current study investigated the effect of 2 different types of unilateral resistance training on the postural Tremor output of 19 neurologically healthy men age 70–80 yr. The strength- (n = 7) and coordination-training (n = 7) groups trained twice a week for 6 wk, performing dumbbell biceps curls, wrist flexions, and wrist extensions, while the control group (n = 5) maintained their normal activities. Changes in index-Finger Tremor (RMS amplitude, peak, and proportional power) and upper limb muscle coactivation were assessed during 4 postural conditions that were performed separately with the trained and untrained limbs. The 2 training groups experienced significantly greater reductions in mean RMS Tremor amplitude, peak, and proportional Tremor power 8–12 Hz and upper limb muscle coactivation, as well as greater increases in strength, than the control group. These results further demonstrate the benefits of resistance training for improving function in older adults.
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Differential time- and frequency-dependent structure of postural sway and Finger Tremor in Parkinson's disease
Neuroscience letters, 2008Co-Authors: Steven Morrison, Karl M Newell, Graham K. Kerr, Peter A. SilburnAbstract:The time- and frequency-dependent patterns of standing balance centre of pressure (COP) and Finger postural/resting Tremor of 12 older individuals and eight age-matched Parkinsonian (PD) participants (on/off medication) were investigated. Tremor and COP data were analysed using measures of signal amplitude (RMS), time-dependent structure (approximate entropy, ApEn), time–frequency analysis and synchrony (Cross ApEn). Results showed that the PD individuals had significantly greater Tremor amplitude and COP excursions in comparison to controls. Differences in the time-dependent structure were also observed between groups. In comparison to the elderly, the resting/postural Tremor output of the PD subjects was more regular (lower ApEn). However, for the postural measures, a reciprocal pattern was observed with the COP being more complex (higher ApEn). All group differences were magnified when the PD individuals were off their medication. There was also greater synchrony between Tremor and postural sway for the PD individuals, indicating a high degree of association between these motor outputs. These results are consistent with the view that the neural signal driving the enhanced limb Tremor in PD is propagated throughout the motor system, consequently emerging within the postural sway dynamics. This commonality of motor output may be a contributing factor in the differential pattern in the dynamics of effector signal structure in PD as a function of task.
Karl M Newell - One of the best experts on this subject based on the ideXlab platform.
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Differences in postural Tremor dynamics with age and neurological disease
Experimental Brain Research, 2017Co-Authors: Steven Morrison, Karl M Newell, Justin J. KavanaghAbstract:The overlap of dominant Tremor frequencies and similarly amplified Tremor observed for Parkinson’s disease (PD) and essential Tremor (ET) means differentiating between these pathologies is often difficult. As Tremor exhibits non-linear properties, employing both linear and non-linear analyses may help distinguish between the Tremor dynamics of aging, PD and ET. This study was designed to examine postural Tremor in healthy older adults, PD and ET using standard linear and non-linear metrics. Hand and Finger postural Tremor was recorded in 15 healthy older adults (64 ± 6 years), 15 older individuals with PD (63 ± 6 years), and 10 persons with ET (68 ± 7 years). Linear measures of amplitude, frequency, and between-limb coupling (coherence) were performed. Non-linear measures of regularity (ApEn) and coupling (Cross-ApEn) were also used. Additionally, receiver operating characteristic analyses were performed for those measures that were significantly different between all groups. The results revealed that the linear measures only showed significant differences between the healthy adults and ET/PD persons, but no differences between the two neurological groups. Coherence showed higher bilateral coupling for ET but no differences in inter-limb coupling between PD and healthy subjects. However, ApEn values for Finger Tremor revealed significant differences between all groups, with Tremor for ET persons being more regular (lower ApEn) overall. Similarly, Cross-ApEn results also showed differences between all groups, with ET persons showing strongest inter-limb coupling followed by PD and elderly. Overall, our findings point to the diagnostic potential for non-linear measures of coupling and Tremor structure as biomarkers for discriminating between ET, PD and healthy persons.
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load induced changes in older individual s hand Finger Tremor are ameliorated with targeting
Journal of the Neurological Sciences, 2014Co-Authors: Justin J. Kavanagh, Karl M Newell, Troy J Cross, Steven MorrisonAbstract:Abstract The purpose of this study was to investigate hand–Finger Tremor dynamics when a load was applied to the Finger in a group of healthy older adults. Moreover, we sought to determine if projecting a representation of the subject's Finger Tremor on a target was capable of overcoming the effects of loading so that hand–Finger interactions returned to a state that was similar to normal Tremor. Eight healthy older males (67 ± 1 year) performed a postural pointing task, where Tremor was assessed using lightweight accelerometers attached to the hand and Finger. Tremor was then assessed when a laser pointer was attached to the Finger and switched off (the load), and then with the laser pointer attached and switched on pointing at targets of 40 mm and 20 mm in diameter. The main findings of this study were that 1) loading the Finger resulted in a reduction in Finger Tremor amplitude and increased Finger Tremor regularity, but no change in hand Tremor, 2) loading caused increased hand–Finger 8–12 Hz cross wavelet coherence and phase synchrony, and 3) pointing at different targets while the Finger was loaded resulted in an increase in Finger Tremor amplitude, and changes in inter-segmental coupling to the extent that hand–Finger dynamics reflected normal unloaded conditions. Overall, these results illustrate that the damping effects of limb loading can be offset, in part, by altering the accuracy demands of the task to make the pointing action more challenging.
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Differential time- and frequency-dependent structure of postural sway and Finger Tremor in Parkinson's disease
Neuroscience letters, 2008Co-Authors: Steven Morrison, Karl M Newell, Graham K. Kerr, Peter A. SilburnAbstract:The time- and frequency-dependent patterns of standing balance centre of pressure (COP) and Finger postural/resting Tremor of 12 older individuals and eight age-matched Parkinsonian (PD) participants (on/off medication) were investigated. Tremor and COP data were analysed using measures of signal amplitude (RMS), time-dependent structure (approximate entropy, ApEn), time–frequency analysis and synchrony (Cross ApEn). Results showed that the PD individuals had significantly greater Tremor amplitude and COP excursions in comparison to controls. Differences in the time-dependent structure were also observed between groups. In comparison to the elderly, the resting/postural Tremor output of the PD subjects was more regular (lower ApEn). However, for the postural measures, a reciprocal pattern was observed with the COP being more complex (higher ApEn). All group differences were magnified when the PD individuals were off their medication. There was also greater synchrony between Tremor and postural sway for the PD individuals, indicating a high degree of association between these motor outputs. These results are consistent with the view that the neural signal driving the enhanced limb Tremor in PD is propagated throughout the motor system, consequently emerging within the postural sway dynamics. This commonality of motor output may be a contributing factor in the differential pattern in the dynamics of effector signal structure in PD as a function of task.
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limb stiffness and postural Tremor in the arm
Motor Control, 2000Co-Authors: Steven Morrison, Karl M NewellAbstract:The relation between limb stiffness and postural Tremor in the upper arm was investigated during a pointing task. The task goal was to minimize the amount of motion (Tremor) at the index Finger under levels of increasing limb stiffness. This study investigated the influence of increasing limb stiffness on the pattern of intra- and interlimb dynamics. The frequency profile of the Tremor for all limb segments across all conditions displayed two peaks, one between 2-4 Hz and another between 8-12 Hz. A third, higher frequency component (20-22 Hz) was present in the index Finger. Increasing limb stiffness through voluntary co-contraction of antagonistic muscle pairs effectively constrained the segments of the upper limb to increasingly operate as a single biomechanical degree of freedom. Higher levels of limb stiffness typically led to an increase in the frequency and power of the 2-4 and 8-12 Hz peaks. There was also a decrease in the frequency of the 20-22 Hz component of Finger Tremor. The act of reducing t...
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postural and resting Tremor in the upper limb
Clinical Neurophysiology, 2000Co-Authors: Steven Morrison, Karl M NewellAbstract:Abstract Objective : Tremor from multiple segments of the upper limb was recorded under postural and resting conditions. The aims of this study were to examine the nature of Tremor within a single limb segment, intra- and inter-limb co-ordination of Tremor, and the influence of cardiac mechanical events on physiological Tremor. Methods : Tremor was recorded from eight healthy adult subjects during a postural pointing task where the level of support for the upper limb segments was successively increased. The dynamics of Tremor within a single segment were examined using power spectral, ApEn and amplitude analyses. Inter-segment Tremor relations were determined using coherence and Cross-correlation analyses. Results : Single segment analysis demonstrated that each (unsupported) limb segment contained two major frequency peaks (at 1–4 Hz and 8–12 Hz). Both peaks were still evident in the distal segments when the proximal segments were supported. External support of the more proximal limb segments also resulted in decreased Finger Tremor, but these changes were not simply additive over segments within a limb or equal across Fingers. There were significant relations between adjacent proximal and distal limb segment pairs but no correlations between contralateral limb segments or between heart rate and limb Tremor. Conclusions : These findings imply that: the low frequency component (1–4 Hz) of physiological Tremor in the hand and Finger could not be attributed to passive transmission of oscillations from the upper arm and forearm; and the contribution of proximal segments on Tremor in the index Finger Tremor could not be predicted from mechanical principles alone. The minimization of Finger Tremor involved compensatory coupling of segments of the upper arm with particular emphasis upon active control of the wrist joint.
Brian J Lipworth - One of the best experts on this subject based on the ideXlab platform.
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pharmacokinetics and systemic β2 adrenoceptor mediated responses to inhaled salbutamol
British Journal of Clinical Pharmacology, 2002Co-Authors: Stephen J Fowler, Brian J LipworthAbstract:AIMS: To examine whether systemic beta2-adrenoceptor responses, such as tachycardia, Tremor and hypokalaemia, can be used as a surrogate for the 20 min pharmacokinetic profile of inhaled salbutamol. METHODS: A retrospective analysis of eight separate published studies in healthy volunteers was performed, each with an identical protocol evaluating the early lung absorption profile of a nominal 1200 microg dose of salbutamol given by different inhaler devices. Peak postural Finger Tremor, plasma potassium and heart rate were assessed. RESULTS: We found the maximum (Cmax) and average (Cav) plasma concentrations of salbutamol to be correlated (P < 0.0001) to change in plasma potassium (Cmax r = 0.904; Cav r = 0.899) and Tremor (Cmax r = 0.875; Cav r = 0.857). No significant correlations existed between change in heart rate and Cmax (r = 0.425) or Cav (r = 0.415). CONCLUSIONS: Systemic beta2-adrenoceptor responses, in particular hypokalaemia and Tremor, but not heart rate, appear to be good surrogates for evaluating the lung delivery of inhaled salbutamol. Consequently it is suggested that potassium or Tremor responses may be used to evaluate the relative lung delivery of salbutamol from different inhaler devices.
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evaluation of in vivo partial beta 1 beta 2 agonist activity a dose ranging study with carteolol
British Journal of Clinical Pharmacology, 1992Co-Authors: N M Wheeldon, D G Mcdevitt, Brian J LipworthAbstract:Abstract 1. The aims of this study were to investigate the partial agonist profile of carteolol and evaluate methodology for differentiating relative beta 1 and beta 2 partial agonist activity (PAA) in vivo. 2. Eight normal subjects received single oral doses of carteolol 10 mg, 30 mg and 60 mg; nadolol 40 mg; pindolol 30 mg and placebo, given in a single-blind, randomised crossover design. 3. beta 1-PAA was demonstrated with carteolol by dose-related increases in resting heart rate and systolic blood pressure, and a plateau in the dose-response curve for attenuation of exercise tachycardia. beta 2-PAA with carteolol was evidenced by a dose-related increase in resting Finger Tremor and progressive attenuation of exercise-induced hyperkalaemia. beta 2-adrenoceptor antagonism was shown by attenuation of terbutaline induced hypokalaemic, chronotropic and Finger Tremor responses. 4. Carteolol behaved as a non-selective beta-adrenoceptor antagonist with both beta 1 and beta 2-PAA components. In the standard clinical dose range of 10-30 mg, its in vivo PAA effects were relatively beta 1-selective. Thus at low doses, there appeared to be a dissociation between selectivity of antagonist and partial agonist activity. 5. Attenuation of exercise hyperkalaemia appears to be a novel and sensitive method for the evaluation of beta 2-PAA in vivo.
Christian Duval - One of the best experts on this subject based on the ideXlab platform.
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the organization of upper limb physiological Tremor
European Journal of Applied Physiology, 2012Co-Authors: Benoit Carignan, Jeanfrancois Daneault, Christian DuvalAbstract:The objectives of this study are (1) to assess the relationship between Tremor displacement of different segments of the upper limb, (2) to assess whether an attempt to voluntarily reduce Tremor amplitude affects this relationship. Twenty-five young healthy participants were tested. Tremor of the Finger, hand, arm and shoulder was assessed using laser displacement sensors while the upper limb was in a postural position. Results show strong correlations (r > 0.90), high coherence (>0.9) and in-phase movement between Tremor displacement oscillations of different segments. The majority of Finger Tremor amplitude can be predicted by angular movement generated at the shoulder joint (r 2 > 0.86). Participants were able to voluntarily reduce Tremor amplitude, but no change in the relationship between segments was observed. Tremor of all segments of the upper limb was mechanically driven by the angular movement generated at the shoulder joint. This study provides evidence that there is no compensatory organization of physiological Tremor. This lays the groundwork to evaluate whether pathological Tremors also lack this organization.
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Assessment of the amplitude of oscillations associated with high-frequency components of physiological Tremor: impact of loading and signal differentiation
Experimental Brain Research, 2005Co-Authors: Christian Duval, Jennifer JonesAbstract:The goal of this study was accurate quantification of the amplitude of high-frequency components of physiological Tremor (PT) in units of displacement, velocity, and acceleration. In addition, changes of amplitude with Finger loading were compared within specific frequency bands. Index Finger Tremor was measured for 20 healthy subjects using a high-resolution laser, simultaneously with an accelerometer, under two conditions, unloaded and loaded (70 g). By use of an accurate filtering technique, oscillations within six predetermined frequency bands were isolated. Results showed that overall mean Tremor amplitude under the unloaded condition was 0.0973 mm in displacement units, 4.525 mm s^−1 in velocity units, and 301.526 mm s^−2 in acceleration units. Although the mean amplitude of oscillations located within the 16.5–30 Hz band was 0.009 mm and represented only 10% of total Tremor amplitude, amplitude of acceleration within the 16.5–30 Hz band was 191 mm s^−2 and represented 60% of total acceleration amplitude. Mean amplitude increased significantly with loading (displacement, t =−2.67, P =0.015; velocity, t =−4.33, P =0.000; acceleration, t =−3.48, P =0.002) but the magnitude of that change was different in each frequency band and its relative importance depended on the level of signal differentiation. Velocity was the only measure that retained sensitivity to changes in amplitude with loading in the low and high-frequency components of PT. In conclusion, this study provides, for the first time, accurate quantification of the amplitude of oscillation of high-frequency components of PT. In addition, it provides clear evidence that the velocity of Tremor oscillation is more suitable for detection of the impact of Finger loading because it enables detection of amplitude changes in both the low and high-frequency components of PT.
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evidence that ventrolateral thalamotomy may eliminate the supraspinal component of both pathological and physiological Tremors
Experimental Brain Research, 2000Co-Authors: Christian Duval, Michel Panisset, Gilles Bertrand, Abbas F SadikotAbstract:Ventrolateral (VL) thalamotomy produced a marked reduction of oscillations related to the supraspinal components of Parkinson's disease Tremor (4-7 Hz) and physiological Tremor (8-12 Hz). Finger Tremor was examined in nine patients undergoing unilateral VL thalamotomy and in nine age-matched controls. In comparison to the preoperative state, the relative percentage of power within the 7.6-12.5 Hz band did not increase after the surgical procedure. Furthermore, the amount of absolute power within the 7.6-12.5 Hz band was much lower for post-surgical patients in comparison to matched controls when periods of Tremor having equal amplitudes were compared. These results suggest that VL thalamotomy interrupts a common circuit involved in the supraspinal component of both physiological and pathological Tremors. We provide evidence that the thalamus may be involved in circuits generating physiological Tremor in humans.
Rod Barrett - One of the best experts on this subject based on the ideXlab platform.
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Differences in Multiple Segment Tremor Dynamics Between Young and Elderly Persons
2014Co-Authors: Steven Morrison, Peter Mills, Rod BarrettAbstract:Background. Physiological Tremor is an intrinsic and highly variable motor output that is sensitive to alteration in both neuromuscular function and/or changing task demands. Given that any Tremor increase can severely influence fine motor performance, there is a requirement to clarify what factors lead to increased Tremor. Identification of those factors that alter Tremor may be particularly pertinent for elderly persons, who often exhibit a decline in postural control and amplified Tremor. The aim of this study was to examine the effect of whole body posture (seated vs standing) on multiple segment Tremor and forearm electromyogram (EMG) activity of younger and older individuals. Methods. Fourteen older and 12 young participants performed a bilateral pointing task. Tremor data were collected using accelerometers attached to the forearm, hand, and Finger segments of each arm. Surface EMG data were also collected from the extensor digitorum muscle of each arm. Results. Although the pattern of Tremor was similar between age groups, older participants exhibited increased hand and Finger Tremor amplitude and increased EMG activity across all postural conditions. For older individuals, Tremor increases were greatest when the participant performed the task in a standing position. All age-related increases in hand and/or Finger Tremor were confined to increases in peak power between 8 Hz and 12 Hz. Conclusions. From a clinical perspective, these findings illustrate that using multiple segment Tremor analyses can provide additional insight into potential age-related Tremor differences. Additionally, the fact that postural position ha
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strength and coordination training are both effective in reducing the postural Tremor amplitude of older adults
Journal of Aging and Physical Activity, 2010Co-Authors: Justin W.l. Keogh, Steven Morrison, Rod BarrettAbstract:The current study investigated the effect of 2 different types of unilateral resistance training on the postural Tremor output of 19 neurologically healthy men age 70–80 yr. The strength- (n = 7) and coordination-training (n = 7) groups trained twice a week for 6 wk, performing dumbbell biceps curls, wrist flexions, and wrist extensions, while the control group (n = 5) maintained their normal activities. Changes in index-Finger Tremor (RMS amplitude, peak, and proportional power) and upper limb muscle coactivation were assessed during 4 postural conditions that were performed separately with the trained and untrained limbs. The 2 training groups experienced significantly greater reductions in mean RMS Tremor amplitude, peak, and proportional Tremor power 8–12 Hz and upper limb muscle coactivation, as well as greater increases in strength, than the control group. These results further demonstrate the benefits of resistance training for improving function in older adults.
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augmented visual feedback increases Finger Tremor during postural pointing
Experimental Brain Research, 2004Co-Authors: Justin W.l. Keogh, Steven Morrison, Rod BarrettAbstract:Physiological Tremor in the upper limb of eight adults was examined during the performance of a unilateral pointing task under conditions where the visual feedback, limb used and target size were altered. All subjects were required to aim a hand-held laser pointer at a circular target 5.5 m away with the goal of keeping the laser emission within the centre of the target. Visual feedback was defined as either normal vision (NV) of their limb Tremor, where the laser was switched off, or augmented vision (AV) where the laser was switched on. Postural Tremor from the segments of the upper limb, forearm muscle EMG activity, and target accuracy measures were recorded and analysed in the time and frequency domains. Accuracy-Tremor relations were assessed using cross correlation and linear regression. Results revealed a high degree of similarity in the general pattern of the Tremor output seen for each limb segment across conditions with only scalar (amplitude) changes being seen as a function of the different constraints imposed. For any single condition the Tremor amplitude increased from proximal to distal segments. The frequency profile for the Tremor in any segment displayed two prominent frequency peaks (at 2-4 Hz and 8-12 Hz). A third, higher frequency peak (18-22 Hz) was observed in the index Fingers only. Across all conditions significant coupling relations were observed only between the hand-Finger and forearm-upper arm segment pairs. Altering the visual feedback was shown to have the greatest effect on limb Tremor with increased Tremor and EMG activity and decreased coupling being seen under AV conditions. In trying to reduce Tremor output when the augmented feedback was provided novice subjects instead increased muscle activity which resulted in increased Tremor. Overall these results indicate that the physiological Tremor output observed in neurologically normal subjects is not simply the product of intrinsic oscillations but is influenced by the nature of the task being performed.