# Limitations in Maximum Intensity Front Crawl in Swimmers with Down Syndrome
## 1 Introduction  
Down Syndrome (DS), a common form of intellectual and relational disability, is a genetic disorder with an estimated incidence ranging from 1 in 1000 to 1 in 1200 live births [1]. A lower metabolic rate, endocrine abnormalities, poor muscle tone, reduced physical activity, and often inadequate nutrition combine to create the typical picture of fragility that often accompanies such individuals, making them susceptible to higher incidences of cardiovascular disease, diabetes, osteoporosis, and obesity [2, 3]. Among the different sports activities, swimming seems to counteract the tendency toward obesity in persons with DS and helps to increase strength, speed, and balance [4, 5]. Regarding the muscular system, individuals with DS show typical muscle hypotonia and joint hyper-flexibility due to ligament laxity [6, 7]. This hyper-flexibility affects muscle strength and power, as well as gait and motor development, usually leading to delayed reflexes, arthritis, early-onset osteoporosis (resulting in long-bone fractures), increased fatigue, scoliosis, excessive dorsal kyphosis, and both lumbar and cervical hyper-lordosis [8]. In addition, children with DS often experience delays in sensory processing patterns and motor skills [9]. Therefore, habititative and rehabilitative interventions tailored to enhance motor and cognitive skills are crucial [10]. Indeed, with appropriate support, individuals with DS can achieve high levels of autonomy, as reported in a recent systematic review [11]. As physical activity is so important, engaging in sports positively influences aerobic parameters, muscular strength, body composition, and psychological well-being in persons with DS, also increasing their overall daily physical activity level [12]. In addition, sports provide opportunities for socialization, personal growth, improved self-esteem, and the prevention of depression [13]. Sports activities like dance, martial arts, and gymnastics are beneficial for enhancing skills such as balance, coordination, and agility. These tasks require complex motor planning and bilateral synchronization, which can enhance both cognitive and physical abilities. Likewise, engaging in outdoor activities like cycling and hiking offers a variety of sensory stimuli that enhance sensory processing and motor control. Apart from individual sports, participation in team sports also has great benefits for persons with DS. Playing soccer or basketball can improve physical fitness and foster social abilities, including communication and teamwork. Moreover, adaptive modalities such as yoga and Pilates can augment core strength, stability, and mindfulness, thus promoting both physical and mental well-being. Overall, diverse sport-related possibilities assist the development of motor and cognitive abilities in persons with DS, with the final aim of promoting increased autonomy and social integration [11]. Certain precautions should, however, be considered, such as monitoring cardiovascular activity during strength training, using appropriate equipment, and adjusting exercise intensity and frequency. Exercises and activities that involve hyperextension should be avoided to prevent hernias, dislocations, strains, and sprains. Instead, exercises that strengthen the stabilizing muscles and stimulate proprioception while maintaining joint integrity are recommended. Monitoring sports activity in water is more challenging than on land, and very little data are available on sports activity at competitive levels in athletes with DS [14]. It is important to obtain these data to understand (a) whether there are safety reasons for not reaching the maximal levels of cardiovascular activation in athletes with DS and (b) to assess the variations between athletes with and without DS of equal competitive level to better target training activity in swimmers with DS. The objective of this study was to evaluate the biomechanical and bioenergetic characteristics of maximum-intensity front crawl swimming in competitive athletes with DS.