Inclusion Criteria:  Adult (≥18 years) patient admitted to the ICU of the study site. Patient deemed suitable for active mobilization by the attending physician and physiotherapist. Not expected to be discharged or transferred from the unit within 24 h of enrollment. Functioning arterial catheter in situ.  Exclusion Criteria:  Not able to provide informed consent. Systemic anticoagulation with LMWH/UFH/DOAC in therapeutic dose range for deep vein thrombosis or pulmonary embolism, or dual antiplatelet therapy. If LMWH is administered twice daily, the patient is eligible for participation provided that vascular access is performed at nadir prior to the first daily dose. Clinically significant inherited or acquired disorder of hemostasis. Morbid obesity that interferes with femoral cannulation or doppler measurements. Hemodynamic instability requiring ongoing volume resuscitation with crystalloid solutions or blood products. Lower-limb amputee. Lower-limb artheriosclerotic disease with critical ischemia. Metastatic cancer or active hematological malignancy. Inherited disorder of amino acid metabolism. Chronic muscle, neuromuscular och neurologic disease with prior documentation of clinically significant lower-limb involvement. Pregnancy. CAM-ICU screening positive for delirium. Single organ failure not requiring invasive mechanical ventilation prior to enrollment.