Carlijn A Vernooij | Aix-Marseille University (original) (raw)
Papers by Carlijn A Vernooij
People and animals can move freely, but they must also be able to stay still. How do skeletal mus... more People and animals can move freely, but they must also be able to stay still. How do skeletal muscles economically produce both movement and posture? Humans are well known to have motor units with relatively homogeneous mechanical properties. Thixotropic muscle properties can provide a solution by providing a temporary stiffening of all skeletal muscles in postural conditions. This stiffening is alleviated almost instantly when muscles start to move. In this paper, we probe this behaviour. We monitor both the neural input to a muscle, measured here as extensor muscle electromyography (EMG), and its output, measured as tremor (finger acceleration). Both signals were analysed continuously as the subject made smooth transitions between posture and movement. The results showed that there were marked changes in tremor which systematically increased in size and decreased in frequency as the subject moved faster. By contrast, the EMG changed little and reflected muscle force requirement rather than movement speed. The altered tremor reflects naturally occurring thixotropic changes in muscle behaviour. Our results suggest that physiological tremor provides useful and hitherto unrecognized insights into skeletal muscle's role in posture and movement
Medicine & Science in Sports & Exercise, 2014
Royal Society Open Science, 2016
People and animals can move freely, but they must also be able to stay still. How do skeletal mus... more People and animals can move freely, but they must also be able to stay still. How do skeletal muscles economically produce both movement and posture? Humans are well known to have motor units with relatively homogeneous mechanical properties. Thixotropic muscle properties can provide a solution by providing a temporary stiffening of all skeletal muscles in postural conditions. This stiffening is alleviated almost instantly when muscles start to move. In this paper, we probe this behaviour. We monitor both the neural input to a muscle, measured here as extensor muscle electromyography (EMG), and its output, measured as tremor (finger acceleration). Both signals were analysed continuously as the subject made smooth transitions between posture and movement. The results showed that there were marked changes in tremor which systematically increased in size and decreased in frequency as the subject moved faster. By contrast, the EMG changed little and reflected muscle force requirement ra...
The Journal of physiology, Jan 24, 2015
Human physiological hand tremor has a resonant component. Proof of this is that its frequency can... more Human physiological hand tremor has a resonant component. Proof of this is that its frequency can be modified by adding mass. However, adding mass also increases the load which must be supported. The necessary force requires muscular contraction which will change motor output and is likely to increase limb stiffness. The increased stiffness will partly offset the effect of the increased mass and this can lead to the erroneous conclusion that factors other than resonance are involved in determining tremor frequency. Using a human centrifuge to increase head-to-foot gravitational field strength, we were able to control for the increased effort by increasing force without changing mass. This revealed that the peak frequency of human hand tremor is 99% predictable on the basis of a resonant mechanism. We ask what, if anything, the peak frequency of physiological tremor can reveal about the operation of the nervous system. This article is protected by copyright. All rights reserved.
Zeitschrift für Psychologie, 2012
The ability to create stone tools is considered an important step in the emergence of human cogni... more The ability to create stone tools is considered an important step in the emergence of human cognition. To further our understanding of these evolutionary processes we focused on the initial learning processes with which this percussive skill may be acquired. We studied a hammering task in which participants had to create a ground force vector by hitting a target on a force plate with a hammerstone. The produced ground force vector was presented as an arrow on a computer screen and had to end in a displayed target. The target could vary in its angle of azimuth and inclination. Over 5 days, three of the five participants adapted a wrist joint angle and two of these three participants adapted a shoulder joint angle that affected only angle of inclination of the ground force vector. Length and angle of azimuth of the ground force vector were not affected. In learning to control a hammering task, the first parameter to be manipulated seems to be the angle of inclination by adjusting the ...
Journal of Neurophysiology, 2015
Two frequency peaks of variable preponderance have been reported for human physiological finger t... more Two frequency peaks of variable preponderance have been reported for human physiological finger tremor. The high-frequency peak (20–25 Hz, seen only in postural tremor) is generally attributed to mechanical resonance, whereas the lower frequency peak (8–12 Hz, seen in both postural and kinetic tremor) is usually attributed to synchronous central or reflexive neural drive. In this study, we determine whether mechanical resonance could generate both peaks. In relaxed subjects, an artificial finger tremor was evoked by random mechanical perturbations of the middle finger or random electrical muscular stimulation of the finger extensor muscle. The high and the low frequencies observed in physiological tremor could both be created by either type of artificial input at appropriate input intensity. Resonance, inferred from cross-spectral gain and phase, occurred at both frequencies. To determine any neural contribution, we compared truly passive subjects with those who exhibited some elect...
The Journal of Physiology, 2012
• Postural physiological hand tremor has a prominent component at ∼8 Hz unlike the associated EMG... more • Postural physiological hand tremor has a prominent component at ∼8 Hz unlike the associated EMG. Consequently, the gain between EMG and tremor is sharply peaked at ∼8 Hz. • Deduction and a simple model using pre-recorded EMG or random noise as an input show that the ∼8 Hz peak is a consequence of resonance. • During voluntary movement the gain peak enlarges and shifts to a lower frequency but the EMG spectrum shows no corresponding changes. This reflects muscle thixotropy. Adjustment of the muscle properties of the model reproduces the effect. • These findings suggest that the rhythm of hand tremor in posture and movement is related to muscle and limb mechanics rather than a neural oscillator. • The discovery that the gain relating EMG to acceleration is very different when static and moving has implications for the control of movement in health and disease.
Journal of Neurophysiology, 2013
There is a debate in the literature about whether the low- and high-frequency peaks of physiologi... more There is a debate in the literature about whether the low- and high-frequency peaks of physiological finger tremor are caused by resonance or central drive. One way to address this issue is to examine the consequences of eliminating, as far as possible, the resonant properties or the voluntary drive. To study the effect of minimizing resonance, finger tremor was recorded under isometric conditions and compared with normal isotonic tremor. To minimize central drive, finger tremor was generated artificially by broad-band electrical stimulation. When resonance was minimized, tremor size declined almost monotonically with increasing frequency. There was no consistent large peak at a frequency characteristic of tremor. Although there was sometimes a peak around the tremor frequency during some isometric conditions, it was extremely small and variable; therefore, any contribution of central drive was minimal. In contrast, there was always a prominent peak in the isotonic frequency spectra...
The American journal of clinical nutrition, 2017
Background: Substantial interindividual variability exists in the maximal rate of fat oxidation (... more Background: Substantial interindividual variability exists in the maximal rate of fat oxidation (MFO) during exercise with potential implications for metabolic health. Although the diet can affect the metabolic response to exercise, the contribution of a self-selected diet to the interindividual variability in the MFO requires further clarification.Objective: We sought to identify whether recent, self-selected dietary intake independently predicts the MFO in healthy men and women.Design: The MFO and maximal oxygen uptake (V̇O2 max) were determined with the use of indirect calorimetry in 305 healthy volunteers [150 men and 155 women; mean ± SD age: 25 ± 6 y; body mass index (BMI; in kg/m(2)): 23 ± 2]. Dual-energy X-ray absorptiometry was used to assess body composition with the self-reported physical activity level (SRPAL) and dietary intake determined in the 4 d before exercise testing. To minimize potential confounding with typically observed sex-related differences (e.g., body com...
Frontiers in aging neuroscience, 2016
Introduction: Aging leads to alterations not only within the complex subsystems of the neuro-musc... more Introduction: Aging leads to alterations not only within the complex subsystems of the neuro-musculo-skeletal system, but also in the coupling between them. Here, we studied how aging affects functional reorganizations that occur both within and between the behavioral and muscular levels, which must be coordinated to produce goal-directed movements. Using unimanual reciprocal Fitts' task, we examined the behavioral and muscular dynamics of older adults (74.4 ± 3.7 years) and compared them to those found for younger adults (23.2 ± 2.0 years). Methods: To achieve this objective, we manipulated the target size to trigger a phase transition in the behavioral regime and searched for concomitant signatures of a phase transition in the muscular coordination. Here, muscular coordination was derived by using the method of muscular synergy extraction. With this technique, we obtained functional muscular patterns through non-negative matrix factorization of the muscular signals followed by...
Medicine & Science in Sports & Exercise, 2016
The aim of this study was to describe maximal fat oxidation (MFO) rates in an athletic population... more The aim of this study was to describe maximal fat oxidation (MFO) rates in an athletic population. In total, 1121 athletes (933 males, 188 females), from a variety of sports and competitive level, undertook a graded exercise test on a treadmill in a fasted state (≥5 h fasted). Rates of fat oxidation were determined using indirect calorimetry. Average MFO was 0.59 ± 0.18 g[BULLET OPERATOR]min, ranging from 0.17 - 1.27 g[BULLET OPERATOR]min. Maximal rates occurred at an average exercise intensity of 49.3 ± 14.8% V˙O2max, ranging from 22.6 - 88.8% V˙O2max. In absolute terms, male athletes had significantly higher MFO compared to females (0.61 and 0.50 g[BULLET OPERATOR]min respectively, P < 0.001). Expressed relative to fat free mass (FFM), MFO were higher in the females compared to males (MFO/FFM: 11.0 and 10.0 mg[BULLET OPERATOR]kg[BULLET OPERATOR]FFM[BULLET OPERATOR]min respectively, P < 0.001). Soccer players had the highest MFO/FFM (10.8 mg[BULLET OPERATOR]kg[BULLET OPERATOR]FFM[BULLET OPERATOR]min), ranging from 4.1 - 20.5 mg[BULLET OPERATOR]kg[BULLET OPERATOR]FFM[BULLET OPERATOR]min, whereas, American Football players displayed the lowest rates of MFO/FFM (9.2 mg[BULLET OPERATOR]kg[BULLET OPERATOR]FFM[BULLET OPERATOR]min). In all athletes, and when separated by sport, large individual variations in MFO rates were observed. Significant positive correlations were found between MFO (g[BULLET OPERATOR]min) and the following variables: FFM, V˙O2max, FATMAX (the exercise intensity at which the MFO was observed), percent body fat (%BF) and duration of fasting. When taken together these variables account for 47% of the variation in MFO. MFO and FATMAX vary significantly between athletes participating in different sports but also in the same sport. Although variance in MFO can be explained to some extent by body composition and fitness status, more than 50% of the variance is not explained by these variables and remains unaccounted for.
Scientific Reports, 2016
The dynamical systems approach addresses Bernstein's degrees of freedom problem by assuming that ... more The dynamical systems approach addresses Bernstein's degrees of freedom problem by assuming that the neuro-musculo-skeletal system transiently assembles and dismantles its components into functional units (or synergies) to meet task demands. Strikingly, little is known from a dynamical point of view about the functioning of the muscular subsystem in this process. To investigate the interaction between the dynamical organisation at muscular and behavioural levels, we searched for specific signatures of a phase transition in muscular coordination when a transition is displayed at the behavioural level. Our results provide evidence that, during Fitts' task when behaviour switches to a different dynamical regime, muscular activation displays typical signatures of a phase transition; a reorganisation in muscular coordination patterns accompanied by a peak in the variability of muscle activation. This suggests that consistent changes occur in coordination processes across the different levels of description (i.e., behaviour and muscles). Specifically, in Fitts' task, target size acts as a control parameter that induces a destabilisation and a reorganisation of coordination patterns at different levels of the neuro-musculo-skeletal system.
Proceedings of the Physiological Society, 2011
ABSTRACT In almost every person there is a clear oscillation at ~10 Hz in the limbs under postura... more ABSTRACT In almost every person there is a clear oscillation at ~10 Hz in the limbs under postural conditions. This postural physiological tremor has been investigated and explained in terms of either mechanical influences (e.g. mechanical resonance of the limb), or neural influences (e.g. rhythmicities of central neural firing) (McAuley and Marsden 2000). We recently showed that human physiological tremor has a strongly mechanical basis (Lakie et al, 2010) and largely results from broad band forcing (EMG) of a resonant system. Here we investigate the effect of altering the forcing by making the muscles ischaemic. With ethical permission we recorded tremor of the outstretched splinted middle finger in 12 subjects (11 male) using a 3 axis accelerometer. One slow movement condition and three postural conditions were studied. Ischaemia was produced by an arm cuff inflated to 150 mm Hg for up to 8 minutes. Surface EMG was recorded from the forearm extensor muscles. Records lasted 60 s each and were repeated 4 times over 2 days. Cross spectral gain between rectified EMG and vertical acceleration was subsequently calculated. Acceleration size was greatly reduced by ischaemia. EMG was if anything slightly increased. Accordingly gain was greatly reduced (Fig 1). Ischaemia is known to substantially reduce tremor size (Christakos et al, 2006). This reduction has been attributed to the effect of ischaemia on muscle spindles (Lippold, 1970) or to its effect on muscle contractile properties (Lakie et al, 2004). The reduction in gain that we see in the present experiments strongly supports the latter explanation.
Proceedings of the Physiological Society, 2012
People and animals can move freely, but they must also be able to stay still. How do skeletal mus... more People and animals can move freely, but they must also be able to stay still. How do skeletal muscles economically produce both movement and posture? Humans are well known to have motor units with relatively homogeneous mechanical properties. Thixotropic muscle properties can provide a solution by providing a temporary stiffening of all skeletal muscles in postural conditions. This stiffening is alleviated almost instantly when muscles start to move. In this paper, we probe this behaviour. We monitor both the neural input to a muscle, measured here as extensor muscle electromyography (EMG), and its output, measured as tremor (finger acceleration). Both signals were analysed continuously as the subject made smooth transitions between posture and movement. The results showed that there were marked changes in tremor which systematically increased in size and decreased in frequency as the subject moved faster. By contrast, the EMG changed little and reflected muscle force requirement rather than movement speed. The altered tremor reflects naturally occurring thixotropic changes in muscle behaviour. Our results suggest that physiological tremor provides useful and hitherto unrecognized insights into skeletal muscle's role in posture and movement
Medicine & Science in Sports & Exercise, 2014
Royal Society Open Science, 2016
People and animals can move freely, but they must also be able to stay still. How do skeletal mus... more People and animals can move freely, but they must also be able to stay still. How do skeletal muscles economically produce both movement and posture? Humans are well known to have motor units with relatively homogeneous mechanical properties. Thixotropic muscle properties can provide a solution by providing a temporary stiffening of all skeletal muscles in postural conditions. This stiffening is alleviated almost instantly when muscles start to move. In this paper, we probe this behaviour. We monitor both the neural input to a muscle, measured here as extensor muscle electromyography (EMG), and its output, measured as tremor (finger acceleration). Both signals were analysed continuously as the subject made smooth transitions between posture and movement. The results showed that there were marked changes in tremor which systematically increased in size and decreased in frequency as the subject moved faster. By contrast, the EMG changed little and reflected muscle force requirement ra...
The Journal of physiology, Jan 24, 2015
Human physiological hand tremor has a resonant component. Proof of this is that its frequency can... more Human physiological hand tremor has a resonant component. Proof of this is that its frequency can be modified by adding mass. However, adding mass also increases the load which must be supported. The necessary force requires muscular contraction which will change motor output and is likely to increase limb stiffness. The increased stiffness will partly offset the effect of the increased mass and this can lead to the erroneous conclusion that factors other than resonance are involved in determining tremor frequency. Using a human centrifuge to increase head-to-foot gravitational field strength, we were able to control for the increased effort by increasing force without changing mass. This revealed that the peak frequency of human hand tremor is 99% predictable on the basis of a resonant mechanism. We ask what, if anything, the peak frequency of physiological tremor can reveal about the operation of the nervous system. This article is protected by copyright. All rights reserved.
Zeitschrift für Psychologie, 2012
The ability to create stone tools is considered an important step in the emergence of human cogni... more The ability to create stone tools is considered an important step in the emergence of human cognition. To further our understanding of these evolutionary processes we focused on the initial learning processes with which this percussive skill may be acquired. We studied a hammering task in which participants had to create a ground force vector by hitting a target on a force plate with a hammerstone. The produced ground force vector was presented as an arrow on a computer screen and had to end in a displayed target. The target could vary in its angle of azimuth and inclination. Over 5 days, three of the five participants adapted a wrist joint angle and two of these three participants adapted a shoulder joint angle that affected only angle of inclination of the ground force vector. Length and angle of azimuth of the ground force vector were not affected. In learning to control a hammering task, the first parameter to be manipulated seems to be the angle of inclination by adjusting the ...
Journal of Neurophysiology, 2015
Two frequency peaks of variable preponderance have been reported for human physiological finger t... more Two frequency peaks of variable preponderance have been reported for human physiological finger tremor. The high-frequency peak (20–25 Hz, seen only in postural tremor) is generally attributed to mechanical resonance, whereas the lower frequency peak (8–12 Hz, seen in both postural and kinetic tremor) is usually attributed to synchronous central or reflexive neural drive. In this study, we determine whether mechanical resonance could generate both peaks. In relaxed subjects, an artificial finger tremor was evoked by random mechanical perturbations of the middle finger or random electrical muscular stimulation of the finger extensor muscle. The high and the low frequencies observed in physiological tremor could both be created by either type of artificial input at appropriate input intensity. Resonance, inferred from cross-spectral gain and phase, occurred at both frequencies. To determine any neural contribution, we compared truly passive subjects with those who exhibited some elect...
The Journal of Physiology, 2012
• Postural physiological hand tremor has a prominent component at ∼8 Hz unlike the associated EMG... more • Postural physiological hand tremor has a prominent component at ∼8 Hz unlike the associated EMG. Consequently, the gain between EMG and tremor is sharply peaked at ∼8 Hz. • Deduction and a simple model using pre-recorded EMG or random noise as an input show that the ∼8 Hz peak is a consequence of resonance. • During voluntary movement the gain peak enlarges and shifts to a lower frequency but the EMG spectrum shows no corresponding changes. This reflects muscle thixotropy. Adjustment of the muscle properties of the model reproduces the effect. • These findings suggest that the rhythm of hand tremor in posture and movement is related to muscle and limb mechanics rather than a neural oscillator. • The discovery that the gain relating EMG to acceleration is very different when static and moving has implications for the control of movement in health and disease.
Journal of Neurophysiology, 2013
There is a debate in the literature about whether the low- and high-frequency peaks of physiologi... more There is a debate in the literature about whether the low- and high-frequency peaks of physiological finger tremor are caused by resonance or central drive. One way to address this issue is to examine the consequences of eliminating, as far as possible, the resonant properties or the voluntary drive. To study the effect of minimizing resonance, finger tremor was recorded under isometric conditions and compared with normal isotonic tremor. To minimize central drive, finger tremor was generated artificially by broad-band electrical stimulation. When resonance was minimized, tremor size declined almost monotonically with increasing frequency. There was no consistent large peak at a frequency characteristic of tremor. Although there was sometimes a peak around the tremor frequency during some isometric conditions, it was extremely small and variable; therefore, any contribution of central drive was minimal. In contrast, there was always a prominent peak in the isotonic frequency spectra...
The American journal of clinical nutrition, 2017
Background: Substantial interindividual variability exists in the maximal rate of fat oxidation (... more Background: Substantial interindividual variability exists in the maximal rate of fat oxidation (MFO) during exercise with potential implications for metabolic health. Although the diet can affect the metabolic response to exercise, the contribution of a self-selected diet to the interindividual variability in the MFO requires further clarification.Objective: We sought to identify whether recent, self-selected dietary intake independently predicts the MFO in healthy men and women.Design: The MFO and maximal oxygen uptake (V̇O2 max) were determined with the use of indirect calorimetry in 305 healthy volunteers [150 men and 155 women; mean ± SD age: 25 ± 6 y; body mass index (BMI; in kg/m(2)): 23 ± 2]. Dual-energy X-ray absorptiometry was used to assess body composition with the self-reported physical activity level (SRPAL) and dietary intake determined in the 4 d before exercise testing. To minimize potential confounding with typically observed sex-related differences (e.g., body com...
Frontiers in aging neuroscience, 2016
Introduction: Aging leads to alterations not only within the complex subsystems of the neuro-musc... more Introduction: Aging leads to alterations not only within the complex subsystems of the neuro-musculo-skeletal system, but also in the coupling between them. Here, we studied how aging affects functional reorganizations that occur both within and between the behavioral and muscular levels, which must be coordinated to produce goal-directed movements. Using unimanual reciprocal Fitts' task, we examined the behavioral and muscular dynamics of older adults (74.4 ± 3.7 years) and compared them to those found for younger adults (23.2 ± 2.0 years). Methods: To achieve this objective, we manipulated the target size to trigger a phase transition in the behavioral regime and searched for concomitant signatures of a phase transition in the muscular coordination. Here, muscular coordination was derived by using the method of muscular synergy extraction. With this technique, we obtained functional muscular patterns through non-negative matrix factorization of the muscular signals followed by...
Medicine & Science in Sports & Exercise, 2016
The aim of this study was to describe maximal fat oxidation (MFO) rates in an athletic population... more The aim of this study was to describe maximal fat oxidation (MFO) rates in an athletic population. In total, 1121 athletes (933 males, 188 females), from a variety of sports and competitive level, undertook a graded exercise test on a treadmill in a fasted state (≥5 h fasted). Rates of fat oxidation were determined using indirect calorimetry. Average MFO was 0.59 ± 0.18 g[BULLET OPERATOR]min, ranging from 0.17 - 1.27 g[BULLET OPERATOR]min. Maximal rates occurred at an average exercise intensity of 49.3 ± 14.8% V˙O2max, ranging from 22.6 - 88.8% V˙O2max. In absolute terms, male athletes had significantly higher MFO compared to females (0.61 and 0.50 g[BULLET OPERATOR]min respectively, P < 0.001). Expressed relative to fat free mass (FFM), MFO were higher in the females compared to males (MFO/FFM: 11.0 and 10.0 mg[BULLET OPERATOR]kg[BULLET OPERATOR]FFM[BULLET OPERATOR]min respectively, P < 0.001). Soccer players had the highest MFO/FFM (10.8 mg[BULLET OPERATOR]kg[BULLET OPERATOR]FFM[BULLET OPERATOR]min), ranging from 4.1 - 20.5 mg[BULLET OPERATOR]kg[BULLET OPERATOR]FFM[BULLET OPERATOR]min, whereas, American Football players displayed the lowest rates of MFO/FFM (9.2 mg[BULLET OPERATOR]kg[BULLET OPERATOR]FFM[BULLET OPERATOR]min). In all athletes, and when separated by sport, large individual variations in MFO rates were observed. Significant positive correlations were found between MFO (g[BULLET OPERATOR]min) and the following variables: FFM, V˙O2max, FATMAX (the exercise intensity at which the MFO was observed), percent body fat (%BF) and duration of fasting. When taken together these variables account for 47% of the variation in MFO. MFO and FATMAX vary significantly between athletes participating in different sports but also in the same sport. Although variance in MFO can be explained to some extent by body composition and fitness status, more than 50% of the variance is not explained by these variables and remains unaccounted for.
Scientific Reports, 2016
The dynamical systems approach addresses Bernstein's degrees of freedom problem by assuming that ... more The dynamical systems approach addresses Bernstein's degrees of freedom problem by assuming that the neuro-musculo-skeletal system transiently assembles and dismantles its components into functional units (or synergies) to meet task demands. Strikingly, little is known from a dynamical point of view about the functioning of the muscular subsystem in this process. To investigate the interaction between the dynamical organisation at muscular and behavioural levels, we searched for specific signatures of a phase transition in muscular coordination when a transition is displayed at the behavioural level. Our results provide evidence that, during Fitts' task when behaviour switches to a different dynamical regime, muscular activation displays typical signatures of a phase transition; a reorganisation in muscular coordination patterns accompanied by a peak in the variability of muscle activation. This suggests that consistent changes occur in coordination processes across the different levels of description (i.e., behaviour and muscles). Specifically, in Fitts' task, target size acts as a control parameter that induces a destabilisation and a reorganisation of coordination patterns at different levels of the neuro-musculo-skeletal system.
Proceedings of the Physiological Society, 2011
ABSTRACT In almost every person there is a clear oscillation at ~10 Hz in the limbs under postura... more ABSTRACT In almost every person there is a clear oscillation at ~10 Hz in the limbs under postural conditions. This postural physiological tremor has been investigated and explained in terms of either mechanical influences (e.g. mechanical resonance of the limb), or neural influences (e.g. rhythmicities of central neural firing) (McAuley and Marsden 2000). We recently showed that human physiological tremor has a strongly mechanical basis (Lakie et al, 2010) and largely results from broad band forcing (EMG) of a resonant system. Here we investigate the effect of altering the forcing by making the muscles ischaemic. With ethical permission we recorded tremor of the outstretched splinted middle finger in 12 subjects (11 male) using a 3 axis accelerometer. One slow movement condition and three postural conditions were studied. Ischaemia was produced by an arm cuff inflated to 150 mm Hg for up to 8 minutes. Surface EMG was recorded from the forearm extensor muscles. Records lasted 60 s each and were repeated 4 times over 2 days. Cross spectral gain between rectified EMG and vertical acceleration was subsequently calculated. Acceleration size was greatly reduced by ischaemia. EMG was if anything slightly increased. Accordingly gain was greatly reduced (Fig 1). Ischaemia is known to substantially reduce tremor size (Christakos et al, 2006). This reduction has been attributed to the effect of ischaemia on muscle spindles (Lippold, 1970) or to its effect on muscle contractile properties (Lakie et al, 2004). The reduction in gain that we see in the present experiments strongly supports the latter explanation.
Proceedings of the Physiological Society, 2012