Sports activity is necessary for children with hemophilia to preserve joints’ range of motion, reduce joint bleeding, improve muscle mass and strength, enhance proprioception and prevent secondary chronic diseases (i.e., cardiovascular disease, diabetes, cancer) ^[5][44]. To prevent joint and muscle bleeding, parents put their children with hemophilia through various exercise programs ^[6][5]. Muscle atrophy, instability and restriction of motion are the first visible signs of sedentarism ^[7][6], whereas early subclinical symptoms such as tender ligaments are found even in clinically healthy young people [1]. This leads to a lack of physical activity and exercise that results in a poor physical condition with diminished muscle strength, aerobic/anaerobic power, proprioception and flexibility ^[8][7]. Furthermore, sports activity can improve bone mineral density, which is lower in children with hemophilia than in healthy peers ^[9][8]. In the past, because of bleeding risk, sports activity was discouraged in children with chronic disease ^[10][9]. However, nowadays, due to new improvements in medical treatment, the participation of children with hemophilia in sport has improved ^[5][44].

However, even if an increase in participation in sports has been observed in children with hemophilia, aerobic activity is less practiced. This phenomenon may be explained considering that children with chronic diseases (such as cystic fibrosis or hemophilia) might have a decline in pulmonary function, which finally leads to less exercise tolerance ^[11][10]. Sports and exercise help to develop fundamental abilities, such as coordination, strength, endurance and flexibility. The muscle-to-fat ratio is improved, and, in the long term, joints are protected and bleeding episodes avoided ^[12][11].

Prophylaxis is effective to maintain a minimum level of clotting factor activity and to permit regular sports participation in children with hemophilia ^[13][12]. However, prophylaxis alone is insufficient to protect from bleeding and joint damage ^[14][13]. In fact, in children with hemophilia, it is important to maintain weight within a healthy range to prevent an overload of the joints, especially the knees and ankle ^[15][14]. Furthermore, sports exercise increases factor VIII levels and could modify coagulation parameters in mild/moderate hemophilia ^[16][15]. It is therefore reported that an increased plasmatic lactate concentration, secondary to anaerobic exercises, for instance, may affect FVIII clearance, thus improving the patient’s coagulation [1].

In the past, high-impact sports were usually prohibited in children with hemophilia due to the high risk of bleeding injuries ^[17][16]. In the 1970s, it was a common practice to discourage any type of sports because of the risk of bleeding episodes, but today, the participation in sports activities by hemophilic patients has improved, and physical activity is considered healthy for this type of patient ^[18][17] even if high-impact sports are still not recommended. Nowadays, on the other hand, different guidelines are available to regulate hemophilic patients’ sports participation; hemophilia type and severity play a key role in the correct sports activity choice ^[19][20][18,19]. According to some hemophilia centers, the choice of activities should reflect individual basis such as: preference/interest, ability, physical condition and resources ^[8][7]. Participation in non-contact sports (swimming, running and walking) should always be promoted, but high-impact sports (rugby, boxing, football and basketball) or sports such as motocross (endowed with a higher injury risk) are often discouraged even on good prophylactic therapy ^[8][12][7,11].

In the United States, the National Hemophilia Foundation (NHF) proposes the stratification of activities into safe, safe-to-moderate, moderate, moderate-to-dangerous and dangerous risk groups. The safe through moderate categories can be routinely recommended with the proper preparation ^[21][20]. Another stratification in high-impact and low-impact sport was proposed by Ross and Goldenberg in 2009: high-impact sports include soccer, basketball, baseball, bowling, gymnastics, field hockey, running, skiing, snowboarding, soccer, softball, tennis and track and field, while low-impact activities include weight training, cycling, Frisbee, golf, swimming and walking/hiking ^[22][21].

However, is it right to forbid children with hemophilia to participate in high-impact sports even if they are on prophylactic treatment?

According to some authors, prophylactic therapy can allow a hemophilic child to engage in vigorous activities or high-impact sports ^[5][44]. An article by Ross et al. ^[22][21] showed that children with hemophilia on prophylaxis could participate without any increased risk of joint bleedings.

The American Academy of Pediatrics (AAP) Committee on Sports Medicine and Fitness has divided childhood activities according to risks and formulated guidelines for sports participation ^[23][22]. The AAP has recommended that children should engage in trampoline activities only in professionally supervised settings due to the high risk of fractures, hospitalization and risk of bruises and other injuries ^[24][23]. For the same reason, no children should participate in boxing because this activity encourages injuries especially to the head and neck ^[25][24]. Additionally, the dangers of concussion related to US football and soccer have recently received attention, with recommendations for carefully monitoring children after an event ^[26][25]. Nonetheless, the AAP recommends participation in sports activities for children with bleeding disorders ^[22][21].

In 2017, the National Hemophilia Foundation (NHF) proposed some guidelines for athletic participation by patients with a bleeding disorder ^[21][20]. Therefore, a minimum of 60 min of exercise per day, with appropriate supervision, is recommended for children after receiving prophylaxis.