The purpose of the study is to show that the intake of L-citrulline improves muscle function in patients with Post-Polio Syndrome (PPS).

This is a single center, randomized, double-blind, placebo controlled study. The study medication consists of L-citrulline, respectively placebo given orally; 5 g L-citrulline or placebo will be given three times daily. The duration of the study is 48 weeks and comprehends one screening and four study visits.

Additionally, in order to investigate whether PPS is associated with an atrophy of spinal cord gray and potentially also white matter as well as motor cortex atrophy, it is planned to offer all trial participants an additional optional spinal cord/brain MRI investigation and a MRI at week 48 and a follow-up one year later together with a clinical and physiotherapy assessment during extension phase. We don't expect Citrulline to affect the spinal cord gray or white and gray matter.

Inclusion Criteria:

• Prior paralytic poliomyelitis with evidence of motor neuron loss
• A period of partial or complete functional recovery after acute paralytic Poliomyelitis
• Slowly progressive and persistent new muscle weakness or decreased endurance, with or without generalized fatigue, muscle atrophy, or muscle and joint pain. Symptoms that persist for at least a year
• Exclusion of other neuromuscular, medical and skeletal abnormalities as causes of symptoms
• Patients older than 18 years at time of Screening
• ambulant
• ability to walk 150m in the 6 min. Walking distance (6MWD)
• females of childbearing potential willing to use contraceptive during the study

Exclusion Criteria:

• Previous (3 months or less) or concomitant participation in any other therapeutic trial
• Use of L-citrulline or L-arginine within the last 3 months
• Known individual hypersensitivity to L-citrulline
• Known or suspected malignancy
• Other chronic disease or clinical relevant limitation of renal, liver, heart function according to discretion of investigator
• Pregnant or breast-feeding women
• Severe renal failure (calculated glomerular filtration rate (GFR) < 30 ml/min)