In persons with severe haemophilia A infused factor VIII half-life and other pharmacokinetic can vary according to determinants such as blood group, von Willebrand factor (VWF) level or age. However, FVIII pharmacokinetics (PK) has not been throughly studied in patients with severe HA as a function of daily physical activity. It si known that vigorous intensity physical activity/exercise can transiently but significantly increase circulating levels of endogenous VWF and consequently FVIII in normal subjects and in patients with moderate or mild haemophilia A. The proposed study is a Proof of Concept one as it will be aimed at investigating the relation between daily physical activity, measured by Sensewear armband device, as number of daily steps and PK variability of infused rec-FVIII concentrate. This kind of investigation has never been done and it is a great interest also for the evaluation of patient's qualitiy of life.

In persons with severe haemophilia A infused factor VIII half-life and other pharmacokinetic can vary according to determinants such as blood group, von Willebrand factor (VWF) level or age. However, FVIII pharmacokinetics (PK) has not been throughly studied in patients with severe HA as a function of daily physical activity. It si known that vigorous intensity physical activity/exercise can transiently but significantly increase circulating levels of endogenous VWF and consequently FVIII in normal subjects and in patients with moderate or mild haemophilia A. The proposed study is a Proof of Concept one as it will be aimed at investigating the relation between daily physical activity, measured by Sensewear armband device, as number of daily steps and PK variability of infused rec-FVIII concentrate. This kind of investigation has never been done and it is a great interest also for the evaluation of patient's qualitiy of life. Physical Examinations at screening and subsequent study visits a physical examination will be performed on the following body systems being described as normal or abnormal: general appearance, headand neck, eyes and ears, nose and throat, heart, abdomen, extremities and joints, lymph nodes and neurological. At screening, if an abnormal condition is detected, the condition will be described on the medical history CRF. At study visit, if a new abnormal or worsened abnormal pre-existing condition is detected, the condition will be described n the CRF.

Inclusion Criteria:

• patients 12-60 yo with severe HA under FVIII concentrates prophylaxis will be selected at the Haemostasis and Thrombosis Center of the Fondazione Policlinico Gemelli IRCCS Rome (FPG)

Exclusion Criteria:

• all patients with malignant tumors or
• patietnts treated with anticoagulant / antiplatelet agents
• patients suffering from other congenital coagulation disorders (von Willebrand disease, other congenital deficiency of coagulation factors or severe thrombocytopenia (< 30,000 Plt/uL)