Biomedical subjects

Inge Zijdewind

Publications and source records attributed to Inge Zijdewind.

12 recordsLinked to original sources

PubMed2007

Reduced cortical activity during maximal bilateral contractions of the index finger.

The bilateral deficit refers to the phenomenon in which homologous muscles produce per muscle less force when contracting simultaneously than when contracting individually. The mechanism underlying the bilateral deficit is still unknown, but the most likely cause is a decline in the activation of motor units during bilateral contractions. In the present study, we used functional magnetic resonance imaging (fMRI) to measure the degree of brain activity during unilateral and bilateral maximal contractions in combination with force and EMG measurements. Subjects performed, in a semi-randomized order, maximal isometric contractions (MVC) with the right index finger, the left index finger and with both fingers simultaneously. During the task, brain activation was measured with a 3 T MR scanner, in combination with force and EMG recordings. The most important activated areas in the brain during the contractions were the sensorimotor cortex (precentral and postcentral gyrus), cerebellum, premotor cortex and supplementary motor area. During bilateral contractions, a significant decline in force and EMG values was found and detailed analysis of the brain activation data showed that this decline was accompanied with a significant decline in the activation of the precentral gyrus. This result suggests that the bilateral decline is the resultant of a decline in input to the primary motor area and shows that the main source of the bilateral deficit lies upstream of the primary motor cortex.

Adult↗

PubMed2006

The origin of activity in the biceps brachii muscle during voluntary contractions of the contralateral elbow flexor muscles.

During strong voluntary contractions, activity is not restricted to the target muscles. Other muscles, including contralateral muscles, often contract. We used transcranial magnetic stimulation (TMS) to analyse the origin of these unintended contralateral contractions (termed "associated" contractions). Subjects (n = 9) performed maximal voluntary contractions (MVCs) with their right elbow-flexor muscles followed by submaximal contractions with their left elbow flexors. Electromyographic activity (EMG) during the submaximal contractions was matched to the associated EMG in the left biceps brachii during the right MVC. During contractions, TMS was delivered to the motor cortex of the right or left hemisphere and excitatory motor evoked potentials (MEPs) and inhibitory (silent period) responses recorded from left biceps. Changes at a spinal level were investigated using cervicomedullary stimulation to activate corticospinal paths (n = 5). Stimulation of the right hemisphere produced silent periods of comparable duration in associated and voluntary contractions (218 vs 217 ms, respectively), whereas left hemisphere stimulation caused a depression of EMG but no EMG silence in either contraction. Despite matched EMG, MEPs elicited by right hemisphere stimulation were approximately 1.5-2.5 times larger during associated compared to voluntary contractions (P < 0.005). Similar inhibition of the associated and matched voluntary activity during the silent period suggests that associated activity comes from the contralateral hemisphere and that motor areas in this (right) hemisphere are activated concomitantly with the motor areas in the left hemisphere. Comparison of the MEPs and subcortically evoked potentials implies that cortical excitability was greater in associated contractions than in the matched voluntary efforts.

Adult↗

PubMed2006

Interaction between force production and cognitive performance in humans.

OBJECTIVE: A dual task paradigm was used to examine the effects of the generation of force on cognitive performance. METHODS: Subjects (n=22) were asked to respond to auditory stimuli with their left middle or index finger and concurrently maintain a sub-maximal contraction with their right index finger at one of two different force levels. The contraction was maintained for approximately 12s and the target force level was alternated between 30 and 60% of the maximal force. Force production was the primary task of interest; performance of the (secondary) choice reaction time task (reaction times and accuracy) was used as an index of the amount of interference between the two tasks. RESULTS: All subjects were capable of performing the force tasks adequately. Significant interference was observed between the level of force production and cognitive performance. At the higher force level, subjects performed the cognitive task more slowly and less accurately compared to the lower force level. CONCLUSION: Our results show that the execution of high-effort motor behaviour interacts with cognitive task performance. However, comparison with the data obtained during fatiguing contractions in a previous study [Lorist MM, Kernell D, Meijman TF, Zijdewind I. Motor fatigue and cognitive task performance in humans. J Physiol 2002;545:313-319.] showed that the interference was stronger during fatiguing contractions than during the present high-effort motor behaviour. SIGNIFICANCE: The results suggest that force-related factors can explain part of the fatigue-related interference between force production and cognitive performance. This result could have consequences for interpreting cognitive deficits observed in patients suffering from motor dysfunction.

Acoustic Stimulation↗

PubMed2006

Fatigue of muscles weakened by death of motoneurons.

Weakness is a characteristic of muscles influenced by the postpolio syndrome (PPS), amyotrophic lateral sclerosis (ALS), and spinal cord injury (SCI). The strength deficits relate to changes in muscle use and to the chronic denervation that can follow the spinal motoneuron death common to these disorders. PPS, ALS, and SCI also involve variable amounts of supraspinal neuron death, the effects of which on muscle weakness remains unclear. Nevertheless, weakness of muscle itself defines the functional consequences of these disorders. A weaker muscle requires an individual to work that muscle at higher than usual intensities relative to its maximal capacity, inducing progressive fatigue and an increased sense of effort. Little evidence is available to suggest that the fatigue commonly experienced by individuals with these disorders relates to an increase in the intrinsic fatigability of the muscle fibers. The only exception is when SCI induces chronic muscle paralysis. To reduce long-term functional deficits in these disorders, studies must identify the signaling pathways that influence neuron survival and determine the factors that encourage and limit sprouting of motor axons. This may ensure that a greater proportion of the fibers in each muscle remain innervated and available for use.

Amyotrophic Lateral Sclerosis↗

PubMed2005

Surface EMG measurements during fMRI at 3T: accurate EMG recordings after artifact correction.

In this experiment, we have measured surface EMG of the first dorsal interosseus during predefined submaximal isometric contractions (5, 15, 30, 50, and 70% of maximal force) of the index finger simultaneously with fMRI measurements. Since we have used sparse sampling fMRI (3-s scanning; 2-s non-scanning), we were able to compare the mean amplitude of the undisturbed EMG (non-scanning) intervals with the mean amplitude of the EMG intervals during scanning, after MRI artifact correction. The agreement between the mean amplitudes of the corrected and the undisturbed EMG was excellent and the mean difference between the two amplitudes was not significantly different. Furthermore, there was no significant difference between the corrected and undisturbed amplitude at different force levels. In conclusion, we have shown that it is feasible to record surface EMG during scanning and that, after MRI artifact correction, the EMG recordings can be used to quantify isometric muscle activity, even at very low activation intensities.

Artifacts↗

PubMed2005

The effect of caffeine on cognitive task performance and motor fatigue.

RATIONALE: In everyday life, people are usually capable of performing two tasks simultaneously. However, in a previous study we showed that during a fatiguing motor task, cognitive performance declined progressively. There is extensive literature on the (positive) effects of caffeine on cognitive and motor performance. These effects are most pronounced under suboptimal conditions, for example during fatigue. However, little is known about the effects of caffeine on cognitive performance during a fatiguing motor task. OBJECTIVE: This study was aimed to investigate whether a moderate dose of caffeine could attenuate the decline in cognitive performance during a fatiguing motor task. METHODS: The study consisted of a placebo and a caffeine (3 mg/kg) session. A total of 23 subjects completed these sessions in a semi-randomized and double-blind order. In each session, subjects performed maximal voluntary contractions of the index finger, a choice reaction time (CRT) task and a dual task consisting of a fatiguing motor task concomitantly with the same CRT task. After the fatiguing dual task, the CRT task was repeated. RESULTS: Caffeine improved cognitive task performance, in both the single and dual task, as shown by decreased reaction times together with unchanged accuracy. Cognitive performance in the dual task deteriorated with increasing fatigue. However, the decrease in cognitive performance in the beginning of the dual task, as observed in the placebo condition, was partly prevented by caffeine administration (i.e., no increase in reaction times). We found no effects of caffeine on motor parameters (absolute force, endurance time or electromyographic amplitude). CONCLUSIONS: Caffeine improved cognitive performance. This effect also extends under demanding situations, as was shown by the performance during the dual task, even during progressive motor fatigue.

Adolescent↗

PubMed2004

Increased blood pressure can reduce fatigue of thenar muscles paralyzed after spinal cord injury.

The aim of this study was to evaluate whether increases in blood pressure, and presumably muscle perfusion pressure, improve the endurance of thenar muscles paralyzed chronically by cervical spinal cord injury (SCI). Resting mean arterial pressure (MAP) was low in all eight subjects (64 +/- 2 mmHg). Muscle fatigue (force decline) was produced on 2 days by intermittent supramaximal electrical stimulation of the median nerve at 20 Hz for 2 min. During one of the fatigue tests, a concurrent sustained voluntary contraction of the contralateral elbow flexors was used to increase resting MAP (by 22%, on average). Although this change in blood pressure resulted in no significant change in mean fatigue for the group, changes in MAP with exercise (median nerve stimulation with and without voluntary contraction) correlated with changes in thenar muscle fatigue in seven subjects. For every 10% increase in MAP, fatigue was reduced by approximately 3%. The data suggest that low blood pressure after chronic cervical SCI and poor blood pressure control during exercise exacerbate the fatigability of paralyzed muscles.

Adult↗

PubMed2003

Effects of imagery motor training on torque production of ankle plantar flexor muscles.

The aim of this study was to investigate in control subjects the effect of imagery training on the torque of plantar-flexor muscles of the ankle. Twenty-nine subjects were allocated to one of three groups that performed either imagery training, low-intensity strength training, or no training (only measurements). The low-intensity training served as an attention control group. Plantar-flexor torques were measured before, during, directly after, and 4 weeks after the training period. At the end of a 7-week training program, significant differences were observed between the maximal voluntary torque production of the imagery training group (136.3 +/- 21.8% of pretraining torque) vs. the low-intensity training group (112.9 +/- 29.0%; P < 0.02) and the control group (113.6 +/- 19.2%; P < 0.02). The results of this study show that imagery training of lower leg muscles significantly increased voluntary torque production of the ankle plantar-flexor muscles and that the force increase was not due to nonspecific motivational effects. Such muscle strengthening effects might be beneficial in rehabilitation for improving or maintaining muscle torque after immobilization.

Adult↗

PubMed2002

Motor unit firing during and after voluntary contractions of human thenar muscles weakened by spinal cord injury.

Spinal cord injury may change both the distribution and the strength of the synaptic input within a motoneuron pool and therefore alter force gradation. Here, we have studied the relative contributions of motor unit recruitment and rate modulation to force gradation during voluntary contractions of thenar muscles performed by five individuals with chronic (>1 yr) cervical spinal cord injury. Mean +/- SD thenar unit firing rates were low during both steady-level 25% (8.3 +/- 2.2 Hz, n = 27 units) and 100% maximal voluntary contractions (MVCs, 9.2 +/- 3.1 Hz, n = 23 units). Thus modest rate modulation, or a lack of it in some units, was seen despite an average fourfold increase in integrated surface electromyographic activity and force. During ramp contractions, units were recruited at 5.7 +/- 2.5 Hz, but still only reached maximal firing rates of 12.8 +/- 4.9 Hz. Motor units were recruited up to 85% of the maximal force achieved (14.6 +/- 5.6 N). In contrast, unit recruitment in control hand muscles is largely complete by 30% MVC. Thus, during voluntary contractions of thenar muscles weakened by cervical spinal cord injury, motor unit rate modulation was limited and recruitment occurred over a wider than usual force range. Those motor units that were stopped voluntarily had significantly lower derecruitment versus recruitment thresholds. However, 8 units (24%) continued to fire long after the signal to end the voluntary contraction at a mean frequency of 5.9 +/- 0.8 Hz. The forces generated by this prolonged unit activity ranged from 0.3 to 7.2% maximum. Subjects were unable to stop this involuntary unit activity even with the help of feedback. The mechanisms that underlie this prolonged motor unit firing need to be explored further.

Adult↗

PubMed2002

Motor fatigue and cognitive task performance in humans.

During fatiguing submaximal contractions a constant force production can be obtained at the cost of an increasing central command intensity. Little is known about the interaction between the underlying central mechanisms driving motor behaviour and cognitive functions. To address this issue, subjects performed four tasks: an auditory choice reaction task (CRT), a CRT simultaneously with a fatiguing or a non-fatiguing submaximal muscle contraction task, and a fatiguing submaximal contraction task alone. Results showed that performance in the single-CRT condition was relatively stable. However, in the fatiguing dual-task condition, performance levels in the cognitive CRT deteriorated drastically with time-on-task. Moreover, in the fatiguing dual-task condition the rise in force variability was significantly larger than during the fatiguing submaximal contraction alone. Thus, our results indicate a mutual interaction between cognitive functions and the central mechanisms driving motor behaviour during fatigue. The precise nature of this interference, and at what level this interaction takes place is still unknown.

Acoustic Stimulation↗

PubMed2002

Motor unit activation order during electrically evoked contractions of paralyzed or partially paralyzed muscles.

The activation order of motor units during electrically evoked contractions of paralyzed or partially paralyzed thenar muscles was determined in seven subjects with chronic cervical spinal cord injury. The median nerve was stimulated percutaneously with pulses of graded intensity to produce increments in the compound electromyogram (EMG) and force. Each increment corresponded to the activation of another unit. The evoked unit EMG and force was obtained by digital subtraction. The thenar muscles had between 15 and 83 units (26 +/- 19) that produced 114.3 +/- 127.1 mN force (n = 290). In six subjects, a significant positive correlation was found between activation order and unit force indicating that weaker units were excited before stronger units. These data are contrary to the notion that a reversal of unit activation order occurs during evoked versus voluntary contractions.

Adult↗

PubMed2002

Patterns of pathological firing in human motor units.

Modulation of motor unit firing rates can change muscle force production. Motor unit firing rates are often reduced during voluntary contractions of muscles influenced by disorders such as stroke or multiple sclerosis, while higher firing rates are typical of muscles innervated by a reduced number of motoneurones. An expanded range of motor unit firing rates is characteristic of disorders in which damage to various systems and neurons occur. Most neuromuscular disorders result in an increase in motor unit discharge variability, in part due to a higher incidence of doublets. In spinal cord injured subjects, long lasting involuntary contractions are common. This activity may reflect persistent inward currents that are revealed due to a lack of (voluntary) inhibition. Some of these changes in motor unit behaviour may actually work to enhance muscle force rather than to reduce it.

Electrophysiology↗