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Several epidemiological studies have shown that regular physical activity is associated with numerous health benefits, reducing the risk for cardiovascular disease (CVD) and other chronic diseases (e.g. obesity, diabetes mellitus, hypertension, depression) as well as improving morbidity, CVD and all-cause mortality (Lee et al., 2014). Exercise is an additional stressor to regular physical activity, a physical loading that enhances energy expenditure and dietary requirements, elevates body temperature and increases the demands on the cardiorespiratory system. Exercise may increase the risk of complications, ranging from musculoskeletal pain and strains to injury, fatigue, illness and hopefully rarely life-threatening disorders. Recent reports suggested a U-shaped relationship between exercise and mainly cardiovascular mortality (Lee et al., 2014). The incidence of sudden cardiac death (SCD) during sports activities varies significantly with age. Recent studies indicate that the rates of exercise-related SCD are around 1:50,000 Athlete-Years (AYs) in young athletes. Multiple studies have reported adverse effects of high intensity and high amount of training and competition load in athletes. 12.5% of the healthy London Marathon runners studied developed exercise-associated hyponatremia, a potentially fatal cause of the collapse (Eijsvogels et al., 2016). Athletes, especially those at the highest levels of their sport, tend to continue exercise and competition, even if they have physical complaints or limitations, increasing the need to use appropriate monitoring tools for safety reasons. The impact of exercise related to SCD and other health disorders is magnified to this specific group. Soft tissue injuries are the most common type of injury in athletes. These can lead to chronic pain, dysfunction, and reoccurrence and are often due to poor conditioning, dehydration, and overtraining. Current methods to assess fatigue, the anaerobic threshold during exertion, as well as the levels of electrolytes level which are essential for the prevention of arrhythmias and collapse, are either inadequate, currently not available or cannot provide real-time information. The vital key to reduce the above is the online monitoring of critical signs, electrolytes, oxygen saturation, pH, glucose, cortisol and lactate levels during exercise.
Elite athletes and sports teams continuously search for methods and opportunities to gain a competitive advantage and improve athletic performance. Since the introduction of heart rate monitors in sports in the mid-70s, several sensors and activity trackers have been proposed to promote an active lifestyle and monitor and assist athletes during training (Merghani et al., 2017). The current state of the art in sport science clinical assessment of athletic performance involves using a plethora of systems and methodologies that are not portable and suitable for field deployment. Due to their bulkiness, they cause discomfort, add weight to the athletes or restrict their movement leading to unrealistic and biased test conditions (white coat effect). These involve traditional ECG (electrocardiography) monitors with large electrodes distributed across the Athlete's body, pulse oxymeters, ergospirometers and blood analysis for metabolite measurements.