Locomotor Muscle Oxygenation and Activation During Acute Interval Compared to Constant-load Bed-cycling Exercise

Inclusion Criteria: * Full cooperatively adult patients indicated by the Adequacy Score of standardized 5 questions (SQ5) = 5/5 * Patients mechanically ventilated for longer than 48 hours during the same ICU admission * Patients are expected to remain in the ICU for more than an additional 48 hours starting from study enrollment * Patients able to perform active cycling for \> 10 consecutive minutes Exclusion Criteria: * Pre-existing functional limitations * Low limb injuries or conditions that would preclude in-bed cycling such as a body habitus unable to fit the bike * Extreme obesity (body mass index \>35 kg/m2) * Neurologically unstable * Acute surgery * Palliative goals of care * Temperature \> 40 °C * An anticipated fatal outcome * Evidence of coronary ischaemia, for example, chest pain or electrocardiogram changes * Resting heart rate \<40 or \>120 beats per minute * Mean arterial pressure \<60 or \>120 mmHg * Peripheral capillary oxygen saturation \< 90% * Wounds, trauma or surgery of leg precluding cycle ergometry * Wounds, trauma or surgery of pelvis precluding cycle ergometry * Wounds, trauma or surgery of lumbar spine precluding cycle ergometry * Coagulation disorder (international normalised ratio \> 1.8, or platelets \< 50,000 mcL) * Intracranial pressure \>20 mm Hg * Femoral access other than femoral central line * Acute deep vein thrombosis * Pulmonary embolism * \>20 mcg/min of noradrenaline * inotropic or vasopressor support comparable to a dose of noradrenaline \>20mcg/min * Fraction of inspired oxygen \> 55% * Arterial partial pressure of oxygen (PaO2) \<65 torr (\<8.66 kPa) * Positive end-expiratory pressure \> 10 cmH2O * Respiratory rate \> 30 breaths per minutes with adequate ventilatory support * Minute ventilation \>150 mL/kg body weight