An interventional study of Exercise test and Active standing test in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), sponsored by Vrije Universiteit Brussel. Active, not recruiting at 1 site in Belgium. Open to participants aged 18 Years to 70 Years, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-11-09.
Sponsored by Vrije Universiteit Brussel · Not applicable, Interventional, and Basic science
The goal of this study is to investigate whether mitochondrial dysfunction is present in patients with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) by subgrouping them into autonomic phenotypes. The main questions it aims to answer are:
Participants will:
ME/CFS is a debilitating disease with unknown pathophysiology. Mitochondrial dysfunction has been proposed as a potential pathophysiological mechanism because the mitochondria are important for energy metabolism. Moreover, patients with mitochondrial diseases experience similar symptoms as patients with ME/CFS, including fatigue, pain and autonomic symptoms. However, literature reports conflicting results regarding mitochondrial dysfunction in patients with ME/CFS. As ME/CFS patients present with a broad range of symptoms, subgrouping them might provide new insights.
Next to mitochondrial dysfunction, the involvement of the autonomic nervous system (ANS) has been proposed as it can be linked to common symptoms such as autonomic symptoms, post-exertional malaise (PEM) and cognitive impairments. Recently, ME/CFS patients were subgrouped into autonomic phenotypes. The presence of autonomic symptoms in patients with mitochondrial diseases highlights that there is a link between the mitochondria and ANS. Although the nature of this link remains unclear, a recent animal study showed that activation of adrenergic receptors - the binding sites of catecholamines (i.e. messengers of the ANS) - increased the production of reactive oxidative species, which are in turn known to influence autonomic function, damage the mitochondria, and regulate mitochondrial DNA methyltransferase (DNMT) expression. Mitochondrial DNMTs are responsible for mtDNA methylation (mtDNAm), which directly affects mitochondrial gene expression and could thus have a major impact on mitochondrial function. Interestingly, Buyn et al. reported that heart rate variability, an important marker to subgroup patients with ME/CFS into autonomic phenotypes, was associated with mtDNAm in a study investigating air pollution in 48 healthy males.
This raises the question whether mitochondrial dysfunction in patients with ME/CFS depends on to which autonomic phenotype they belong and whether this relation can be explained by mtDNAm, which is influenced by reactive oxygen species production upon adrenergic receptor activation. Consequently, this relation may lead to autonomic phenotype-dependent mitochondrial dysfunction. Hence, this project entails a cross-over study designed to clear the conflicting results regarding mitochondrial dysfunction in patients with ME/CFS by subgrouping them into autonomic phenotypes.
The investigators will perform an experimental cross-over study, in which the autonomic phenotypes will be validated and linked to additional biological information (i.e., mitochondrial (dys)function and mitochondrial DNA methylation). Study participants will visit the hospital twice with two weeks in between the visits. During each visit, autonomic, clinical and biological outcomes will be assessed before and after the experimental procedure, which include a single bout of submaximal exercise (Aerobic Power Index) to create a high-energy demand situation and stress the mitochondria, and an orthostatic test (Active Standing test) to stress the autonomic nervous system (ANS). The order of these experimental procedures is defined by randomly dividing all participants into two groups. Additionally, this project will assess the presence and severity of post-exertional malaise (PEM) 24h and 7 days after the experimental procedure via online assessments allowing the investigators to determine whether autonomic phenotype and mitochondrial function can predict PEM severity.
263 studies on the registry are indexed under Fatigue Syndrome, Chronic; 61 are open to participants now.
This study's planned enrollment of 105 is above the median of 60 across 177 interventional studies indexed under Fatigue Syndrome, Chronic.
Browse Fatigue Syndrome, Chronic studies →Vrije Universiteit Brussel is the lead sponsor of 158 studies on the registry; 43 are open to participants now.
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Exclusion Criteria:
Study participants will visit the hospital twice with two weeks in between the visits. During each visit, autonomic, clinical and biological outcomes will be assessed before and after the experimental procedure, which include a single bout of submaximal exercise (Aerobic Power Index) to create a high-energy demand situation and stress the mitochondria, and an orthostatic test (Active Standing test) to stress the autonomic nervous system (ANS). The order of these experimental procedures is defined by randomly dividing all participants into two groups. Additionally, this project will assess the presence and severity of post-exertional malaise (PEM) 24h and 7 days after the experimental procedure via online assessments allowing us to determine whether autonomic phenotype and mitochondrial function can predict PEM severity.
Other: Exercise test · Other: Active standing test
Study participants will visit the hospital twice with two weeks in between the visits. During each visit, autonomic, clinical and biological outcomes will be assessed before and after the experimental procedure, which include a single bout of submaximal exercise (Aerobic Power Index) to create a high-energy demand situation and stress the mitochondria, and an orthostatic test (Active Standing test) to stress the autonomic nervous system (ANS). The order of these experimental procedures is defined by randomly dividing all participants into two groups. Additionally, this project will assess the presence and severity of post-exertional malaise (PEM) 24h and 7 days after the experimental procedure via online assessments allowing us to determine whether autonomic phenotype and mitochondrial function can predict PEM severity.
Other: Exercise test · Other: Active standing test
The Aerobic Power Index (API) will be used to create a high-energy demand situation and stress the mitochondria. Briefly, cycling starts at a constant rate of 70 cycles/min and workload of 25 Watt/min, increasing 25 Watt/min until the patient reaches 75% of the age-predicted maximal heart rate.
Also known as: Aerobic Power Index
The ANS will be stressed via an Active Standing (AS) test, an ecological valid orthostatic test. Subjects will start in a supine position followed by standing up within five seconds, these instructions will be explained to the subjects prior to the start of the AS test. After standing up, the subjects need to maintain an upright posture quietly for seven minutes, afterwards the patients will be returned to the supine position.
Also known as: orthostatic test
Mitochondrial function will be investigated in patients with ME/CFS compaired to healthy controls at baseline and after a physical exercise test.
The primary objective is to examine the difference in mitochondrial function between 75 ME/CFS patients and 30 healthy controls. Mitochondrial function will be determined in isolated peripheral blood mononuclear cells (PBMCs). Following the manufacturer's instructions, the Seahorse XF Cell Mito Stress Test Kit (Agilent) will be used to determine the oxygen consumption rate (OCR).
Time frame: Blood collection immediatly before procedure and after
Autonomic nervous system (ANS) function will be explored in patients with ME/CFS and healthy controls at baseline and after an orthostatic test.
The investigators will explore autonomc nervous system (ANS) function, enabling clinical stratification of 75 patients with ME/CFS. During the othostatic test or active standing test, the ANS will be monitored with the SOMNOTouch NIBP device, providing a non-invasive continuous blood pressure monitoring.
Time frame: During intervention (approximately 45 mins) in hospital
Autonomic nervous system (ANS) function will be explored in patients with ME/CFS and healthy controls at baseline and after an orthostatic test.
The investigators will explore autonomc nervous system (ANS) function, enabling clinical stratification of 75 patients with ME/CFS. During the othostatic test or active standing test, the ANS will be monitored with the SOMNOTouch NIBP device, providing a non-invasive continuous heart rate monitoring.
Time frame: During intervention (approximately 45 mins) in hospital
Autonomic nervous system (ANS) function will be explored in patients with ME/CFS and healthy controls at baseline and after an orthostatic test.
The investigators will explore autonomc nervous system (ANS) function, enabling clinical stratification of 75 patients with ME/CFS. During the othostatic test or active standing test, the ANS will be monitored with the SOMNOTouch NIBP device, providing a non-invasive continuous arterial stiffness measurement.
Time frame: During intervention (approximately 45 mins) in hospital
Prediction of severity of post-exertional malaise in patients with ME/CFS.
Prediction of the severity of early- (24h) post-exertional malaise (PEM) in 75 patients with ME/CFS via online assessments including the Chronic Fatigue Syndrome Symptom List.
Time frame: 24hours after both study visits
Prediction of severity of post-exertional malaise in patients with ME/CFS.
Prediction of the severity of late-onset (7 days) PEM in 75 patients with ME/CFS via online assessments including the Quality of Life Scale (quality of life, health and other areas of life, min score = not at all, max score=absolutely), Fatigue Severity Scale (min score 0=strongly disagree, max score 6=strongly agree), International Physical Activity Questionnaire and Chronic Fatigue Syndrome Symptom List.
Time frame: 7 days after both study visits
Plan to share: No
No publications or documents are linked to this record.
Started Oct 2024 (actual). Primary completion is estimated for Nov 2026, 25 months after the start.
Of 73 non-industry interventional studies with no phase under Fatigue Syndrome, Chronic, half reached primary completion within 24 months of starting (the median), counting those still running; a quarter within 11 and three quarters within 43. This study's planned 25 months is close to that.
Counting every sponsor, half of 78 studies reached it within 23 months; a quarter within 11 and three quarters within 43.
How these figures are worked out, and which studies are left out of them.
From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
This study is active, not recruiting, as verified in Nov 2026. You cannot join it, but the record below documents what was studied.
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