Table 1 Inclusion and exclusion criteria

(1) age 18 years and older

(2) suffering from severe fatigue (CIS-fatigue ≥ 35) [21]

(3) ability to walk independently (ankle-foot orthoses and canes are accepted)

(4) being able to exercise on a bicycle ergometer

(5) being able to complete either type of intervention

Exclusion criteria

(1) cognitive impairment

(2) insufficient mastery of the Dutch language

(3) neurological or orthopedic co-morbidity interfering with the interventions or possibly influencing outcomes

(4) pregnancy

(5) use of psychotropic drugs (except simple sleeping medication)

(6) severe cardiopulmonary disease (chest pain, arrhythmia, pacemaker, cardiac surgery, severe exertional dyspnea, emphysema)

(7) epileptic seizures

(8) poorly regulated diabetes mellitus or hypertension

(9) clinical depression, as diagnosed with the Beck Depression Inventory for primary care (BDI-PC) [22, 23]