Machiel J Zwarts

Radboud University Nijmegen, Nymegen, Gelderland, Netherlands

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Publications (235)723 Total impact

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    ABSTRACT: To investigate the effect of physical training combined with growth hormone (GH) on muscle thickness and its relationship with muscle strength and motor development in infants with Prader-Willi syndrome (PWS). In a randomized controlled trial, 22 infants with PWS (12.9 ± 7.1 months) were followed over 2 years to compare a treatment group (n = 10) with a waiting-list control group (n = 12). Muscle thickness of 4 muscle groups was measured by using ultrasound. Muscle strength was evaluated by using the Infant Muscle Strength meter. Motor performance was measured with the Gross Motor Function Measurement. Analyses of variance were used to evaluate between-group effects of GH on muscle thickness at 6 months and to compare pre- and posttreatment (after 12 months of GH) values. Multilevel analyses were used to evaluate effects of GH on muscle thickness over time, and multilevel bivariate analyses were used to test relationships between muscle thickness, muscle strength, and motor performance. A significant positive effect of GH on muscle thickness (P < .05) was found. Positive relationships were found between muscle thickness and muscle strength (r = 0.61, P < .001), muscle thickness and motor performance (r = 0.81, P < .001), and muscle strength and motor performance (r = 0.76, P < .001). GH increased muscle thickness, which was related to muscle strength and motor development in infants with PWS. Catch-up growth was faster in muscles that are most frequently used in early development. Because this effect was independent of GH, it suggests a training effect. Copyright © 2014 by the American Academy of Pediatrics.
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    ABSTRACT: Non-dystrophic myotonic syndromes represent a heterogeneous group of clinically quite similar diseases sharing the feature of myotonia. These syndromes can be separated into chloride and sodium channelopathies, with gene-defects in chloride or sodium channel proteins of the sarcolemmal membrane. Myotonia has its basis in an electrical instability of the sarcolemmal membrane. In the present study we examine the discriminative power of the resulting myotonic discharges for these disorders. Needle electromyography was performed by an electromyographer blinded for genetic diagnosis in 66 non-dystrophic myotonia patients (32 chloride and 34 sodium channelopathy). Five muscles in each patient were examined. Individual trains of myotonic discharges were extracted and analyzed with respect to firing characteristics. Myotonic discharge characteristics in the rectus femoris muscle almost perfectly discriminated chloride from sodium channelopathy patients. The first interdischarge interval as a single variable was longer than 30 ms in all but one of the chloride channelopathy patients and shorter than 30 ms in all of the sodium channelopathy patients. This resulted in a detection rate of over 95%. Myotonic discharges of a single muscle can be used to better guide towards a molecular diagnosis in non-dystrophic myotonic syndromes.
    Neuromuscular Disorders 10/2014; 25(1). DOI:10.1016/j.nmd.2014.09.014 · 3.13 Impact Factor
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    ABSTRACT: Postcancer fatigue is a frequently occurring problem, impairing quality of life. Little is known about (neuro)physiological factors determining postcancer fatigue. It may be hypothesized that postcancer fatigue is characterized by low peripheral muscle fatigue and high central muscle fatigue.
    Journal of Pain and Symptom Management 08/2014; 49(2). DOI:10.1016/j.jpainsymman.2014.06.020 · 2.74 Impact Factor
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    ABSTRACT: Introduction: We investigated whether muscle ultrasound can distinguish muscles affected by post-polio syndrome (PPS) from healthy muscles and whether severity of ultrasound abnormalities is associated with muscle strength.Methods: Echo intensity, muscle thickness, and isometric strength of the quadriceps muscles were measured in 48 patients with PPS and 12 healthy controls.Results: Patients with PPS had significantly higher echo intensity and lower muscle thickness than healthy controls. In patients, both echo intensity and muscle thickness were associated independently with muscle strength. A combined measure of echo intensity and muscle thickness was more strongly related to muscle strength than either parameter alone.Discussion: Quantitative ultrasound distinguishes healthy muscles from those affected by PPS, and measures of muscle quality and quantity are associated with muscle strength. Hence, ultrasound could be a useful tool for assessing disease severity and monitoring changes resulting from disease progression or clinical intervention in patients with PPS. © 2014 Wiley Periodicals, Inc.
    Muscle & Nerve 04/2014; 51(1). DOI:10.1002/mus.24272 · 2.31 Impact Factor
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    M J Zwarts, J P van Dijk
    Muscle & Nerve 03/2014; 49(3). DOI:10.1002/mus.24103 · 2.31 Impact Factor
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    ABSTRACT: Abnormal excitation and excitability of the cerebral cortex are characteristics of epilepsy. A direct way to measure excitability is with transcranial magnetic stimulation (TMS). In epilepsy, TMS provides information about the epileptic network and the effect of medication thereon. Improving intracortical inhibition shortly after starting an antiepileptic drug is predictive of clinical response in the next year.
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    ABSTRACT: To investigate whether strength decline in post-polio syndrome (PPS) results from excessive distal axonal degeneration of enlarged motor units. We assessed changes over 10years in isometric quadriceps strength, mean motor unit action potential (MUAP) size, root mean squared (RMS) amplitude, and level of interference (LOI) in 47 patients with PPS and 12 healthy controls, using high density surface EMG. At baseline, all patients had symptomatic quadriceps dysfunction, evidenced by transmission defects on single-fibre EMG. MU size and strength declined significantly by 20% and 15%, respectively in patients with PPS. Those with the largest initial MU sizes exhibited the greatest losses of mean MU size (27%) and proportional decreases in quadriceps strength (23%). Initial strength, change in LOI and change in RMS amplitude together explained 35% of the variability in strength changes in patients. MU size of controls did not change, although they lost 29% strength. MU size and strength declined concomitantly in a homogeneous cohort of patients with PPS and quadriceps dysfunction. This long term follow-up study provides evidence that size diminution of enlarged MUs combined with a reduced number of active MUs contributes to the gradual strength decline in PPS.
    Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology 11/2013; 125(6). DOI:10.1016/j.clinph.2013.11.003 · 2.98 Impact Factor
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    ABSTRACT: Introduction: Excitotoxicity plays an important role in the pathogenesis of the preferential motor neuron death observed in ALS. Continuous Theta Burst Stimulation (cTBS) by transcranial magnetic stimulation has an inhibitory effect on corticospinal excitability (CSE). We characterized the neurophysiological changes induced by cTBS in ALS. Methods: The patients received 5 daily sessions of cTBS. CSE was assessed at baseline and after each session of cTBS. Results: The amplitude of a single pulse motor evoked potential was significantly decreased (34%) over the days. The amplitude returned to baseline a week after the last session. The resting motor threshold increased significantly, whereas intracortical inhibition and facilitation did not change over the sessions. Discussion: Daily cTBS has a cumulative depressing effect on CSE in patients with ALS. Our results suggest that modulation of CSE in ALS is possible, but repetitive sessions are needed to maintain the effect. © 2013 Wiley Periodicals, Inc.
    Muscle & Nerve 11/2013; 48(5). DOI:10.1002/mus.23818 · 2.31 Impact Factor
  • Clinical Neurophysiology 10/2013; 124(10):e183. DOI:10.1016/j.clinph.2013.04.324 · 2.98 Impact Factor
  • Clinical Neurophysiology 10/2013; 124(10):e160. DOI:10.1016/j.clinph.2013.04.278 · 2.98 Impact Factor
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    ABSTRACT: Postcancer fatigue is a frequently occurring problem, impairing quality of life. Until now, little is known about (neuro) physiological factors determining postcancer fatigue. For non-cancer patients with chronic fatigue syndrome, certain characteristics of brain morphology and metabolism have been identified in previous studies. We investigated whether these volumetric and metabolic traits are a reflection of fatigue in general and thus also of importance for postcancer fatigue. Fatigued patients were randomly assigned to either the intervention condition (cognitive behavior therapy) or the waiting list condition. Twenty-five patients in the intervention condition and fourteen patients in the waiting list condition were assessed twice, at baseline and six months later. Baseline measurements of 20 fatigued patients were compared with 20 matched non-fatigued controls. All participants had completed treatment of a malignant, solid tumor minimal one year earlier. Global brain volumes, subcortical brain volumes, metabolite tissue concentrations, and metabolite ratios were primary outcome measures. Volumetric and metabolic parameters were not significantly different between fatigued and non-fatigued patients. Change scores of volumetric and metabolic parameters from baseline to follow-up were not significantly different between patients in the therapy and the waiting list group. Patients in the therapy group reported a significant larger decrease in fatigue scores than patients in the waiting list group. No relation was found between postcancer fatigue and the studied volumetric and metabolic markers. This may suggest that, although postcancer fatigue and chronic fatigue syndrome show strong resemblances as a clinical syndrome, the underlying physiology is different. NCT01096641.
    PLoS ONE 09/2013; 8(9):e74638. DOI:10.1371/journal.pone.0074638 · 3.53 Impact Factor
  • H Jacobus Gilhuis, Mahsa Rafiee, Machiel J Zwarts
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    ABSTRACT: A 64-year-old woman had a painful left hand her entire life. Examination revealed hypertrophy of the left arm and hand with an increased muscle bulk of the first dorsal interosseous muscle and ulnar deviation of digits II to V figures 1 and 2). Except for large motor unit potentials with a normal interference pattern, EMG was normal. Brain imaging was normal.
    Neurology 04/2013; 80(15):e170-1. DOI:10.1212/WNL.0b013e31828c2efa · 8.30 Impact Factor
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    ABSTRACT: PURPOSE: Patients suffering from postcancer fatigue have both an inferior physical activity and physical fitness compared to non-fatigued cancer survivors. The aims of this study were (1) to examine the effect of cognitive behavior therapy, an effective treatment for postcancer fatigue, on physical activity and physical fitness and (2) to examine whether the effect of cognitive behavior therapy on postcancer fatigue is mediated by physical activity and/or physical fitness. METHODS: Severely fatigued cancer survivors were randomly assigned to either the intervention (cognitive behavior therapy) or the waiting list condition. After assigning 23 patients in the intervention condition and 14 patients in the waiting list condition, they were assessed both at baseline and 6 months later. Physical activity was assessed via actigraphy and physical fitness was assessed by a maximal exercise test. A nonparametric bootstrap approach was used to test the statistical significance of the mediation effects. RESULTS: A significant increase in physical activity was observed in the intervention group from baseline to follow-up, whereas physical activity did not change from baseline to follow-up in the waiting list group. Physical fitness did not significantly change after cognitive behavior therapy or after 6 months of waiting for therapy. Fatigue decreased more significantly in the intervention group than in the waiting list group. The mediation hypotheses were rejected. CONCLUSIONS: Cognitive behavior therapy effectively reduced postcancer fatigue and increased physical activity but did not change physical fitness. The effect of cognitive behavior therapy on postcancer fatigue is not mediated by a change in physical activity or physical fitness.
    Supportive Care in Cancer 03/2013; DOI:10.1007/s00520-013-1784-9 · 2.50 Impact Factor
  • Neurophysiologie Clinique/Clinical Neurophysiology 01/2013; 43(1):78. DOI:10.1016/j.neucli.2012.11.032 · 1.46 Impact Factor
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    ABSTRACT: OBJECTIVES: Fibromyalgia (FM) is a disorder characterised by chronic widespread pain in soft tissues, especially in muscles. Previous research has demonstrated a higher muscle fibre conduction velocity (CV) in painful muscles of FM patients. The primary goal of this study was to investigate whether there is also a difference in CV in non-painful, non-tender point (TP) related muscles between FM patients and controls. The secondary goal was to explore associations between the CV, the number of TPs and the complaints in FM. METHODS: Surface electromyography (sEMG) was performed on the biceps brachii muscle of female FM patients (13) and matched healthy controls (13). Short static contractions were applied with the arm unloaded and loaded at 5% and 10% of maximum voluntary force. The CV was derived by cross-correlation method (CV-cc) and inter-peak latency method (CV-ipl). TP score and Fibromyalgia Impact Questionnaire (FIQ) were performed in all participants. Correlations were calculated between the CVs, TP score and items of the FIQ. RESULTS: In FM patients, the CV was higher than in the controls (CV-cc p=0.005; CV-ipl p=0.022). The CV was correlated with the number of TPs in FM patients (r=0.642 and 0.672 for CV-cc and CV-ipl, respectively). No correlations were found between the CV and any aspect of health status on the FIQ. CONCLUSIONS: The results demonstrate abnormally high muscle membrane conduction velocity in FM, even in non-TP muscles. In addition, a relationship has been found between the high membrane velocity and the number of TPs.
    Clinical and experimental rheumatology 11/2012; · 2.97 Impact Factor
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    ABSTRACT: Introduction: Fibromyalgia (FM) is a disorder of widespread muscular pain. We investigated possible differences in surface electromyography (sEMG) in clinically unaffected muscle between patients with FM and controls. Methods: sEMG was performed on the biceps brachii muscle of 13 women with FM and 14 matched healthy controls during prolonged dynamic exercises, unloaded, and loaded up to 20% of maximum voluntary contraction. The sEMG parameters were: muscle fiber conduction velocity (CV); skewness of motor unit potential (peak) velocities; peak frequency (PF) (number of peaks per second); and average rectified voltage (ARV). Results: There was significantly higher CV in the FM group. Although the FM group performed the tests equally well, their electromyographic fatigue was significantly less expressed compared with controls (in CV, PF, and ARV). Conclusion: In the patients with FM, we clearly showed functional abnormalities of the muscle membrane, which led to high conduction velocity and resistance to fatigue in electromyography. Muscle Nerve 46: 738-745, 2012.
    Muscle & Nerve 11/2012; 46(5):738-45. DOI:10.1002/mus.23382 · 2.31 Impact Factor
  • Machiel J Zwarts, H Jacobus Gilhuis
    Muscle & Nerve 10/2012; 46(4):611-2. DOI:10.1002/mus.23352 · 2.31 Impact Factor
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    ABSTRACT: PURPOSE: The aim of this study is to examine whether physical fitness of severely fatigued and non-fatigued cancer survivors, as measured by maximal exercise performance, is different between both groups and, if so, whether this difference can be explained by differences in physical activity, self-efficacy regarding the exercise test, and/or social support. METHODS: Severely fatigued (n = 20) and sex- and age-matched non-fatigued (n = 20) disease-free cancer survivors, who completed treatment for a malignant, solid tumor at least 1 year earlier, participated in this case-control study. Maximal oxygen consumption was measured during an incremental cycling exercise test. Physical activity was assessed via actigraphy. Self-efficacy regarding the test and social support were assessed via questionnaires to study its relationship with physical fitness. RESULTS: Maximal oxygen consumption was significantly lower in fatigued compared to non-fatigued participants. Actual physical activity, self-efficacy regarding the test, and negative interactions of social support were significantly different between both groups. However, after inclusion of these three variables in linear regression analyses, the difference in physical fitness between fatigued and non-fatigued cancer survivors persisted. CONCLUSIONS: Maximal oxygen consumption, a measure for physical fitness, was reduced in severely fatigued compared to non-fatigued cancer survivors. The inferior maximal exercise performance cannot fully be explained by differences in physical activity, self-efficacy, or social support between both groups. Other currently still unknown factors, such as a disturbance in the cardiopulmonary circuit, may play a role.
    Supportive Care in Cancer 07/2012; 21(2). DOI:10.1007/s00520-012-1531-7 · 2.50 Impact Factor
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    ABSTRACT: Postcancer fatigue is a frequently occurring, severe, and invalidating problem, impairing quality of life. Although it is possible to effectively treat postcancer fatigue with cognitive behaviour therapy, the nature of the underlying (neuro)physiology of postcancer fatigue remains unclear. Physiological aspects of fatigue include peripheral fatigue, originating in muscle or the neuromuscular junction; central fatigue, originating in nerves, spinal cord, and brain; and physical deconditioning, resulting from a decreased cardiopulmonary function. Studies on physiological aspects of postcancer fatigue mainly concentrate on deconditioning. Peripheral and central fatigue and brain morphology and function have been studied for patients with fatigue in the context of chronic fatigue syndrome and neuromuscular diseases and show several characteristic differences with healthy controls. Fifty seven severely fatigued and 21 non-fatigued cancer survivors will be recruited from the Radboud University Nijmegen Medical Centre. Participants should have completed treatment of a malignant, solid tumour minimal one year earlier and should have no evidence of disease recurrence. Severely fatigued patients are randomly assigned to either the intervention condition (cognitive behaviour therapy) or the waiting list condition (start cognitive behaviour therapy after 6 months). All participants are assessed at baseline and the severely fatigued patients also after 6 months follow-up (at the end of cognitive behaviour therapy or waiting list). Primary outcome measures are fatigue severity, central and peripheral fatigue, brain morphology and function, and physical condition and activity. This study will be the first randomized controlled trial that characterizes (neuro)physiological factors of fatigue in disease-free cancer survivors and evaluates to which extent these factors can be influenced by cognitive behaviour therapy. The results of this study are not only essential for a theoretical understanding of this invalidating condition, but also for providing an objective biological marker for fatigue that could support the diagnosis and follow-up of treatment. The study is registered at (NCT01096641).
    BMC Cancer 06/2012; 12:256. DOI:10.1186/1471-2407-12-256 · 3.32 Impact Factor
  • Muscle & Nerve 03/2012; 45(3):449-50. DOI:10.1002/mus.22254 · 2.31 Impact Factor

Publication Stats

4k Citations
723.00 Total Impact Points


  • 1998–2013
    • Radboud University Nijmegen
      • • Donders Institute for Brain, Cognition, and Behaviour
      • • Donders Centre of Neuroscience (DCN)
      • • Medical Centre
      • • Department of Anesthesiology
      Nymegen, Gelderland, Netherlands
  • 1999–2012
    • Radboud University Medical Centre (Radboudumc)
      • • Department of Human Genetics
      • • Department of Neurology
      • • Department of Rehabilitation
      Nymegen, Gelderland, Netherlands
  • 2008
    • VU University Amsterdam
      Amsterdamo, North Holland, Netherlands
  • 2006
    • University of Freiburg
      Freiburg, Baden-Württemberg, Germany
    • Maastricht University
      • Department of Radiology
      Maestricht, Limburg, Netherlands
  • 2005
    • Erasmus MC
      • Department of Clinical Neurophysiology
      Rotterdam, South Holland, Netherlands
  • 2004
    • Erasmus Universiteit Rotterdam
      • Department of Immunology
      Rotterdam, South Holland, Netherlands
  • 2003
    • VU University Medical Center
      • Rehabilitation Medicine Clinic
      Amsterdamo, North Holland, Netherlands
  • 1993–1995
    • Martini Ziekenhuis
      Groningen, Groningen, Netherlands
  • 1985–1992
    • Universitair Medisch Centrum Groningen
      • Department of Neurology
      Groningen, Groningen, Netherlands
  • 1986–1991
    • University of Groningen
      • Department of Neurology
      Groningen, Groningen, Netherlands