## 3 Results
### Myotonic Disorders
He eventually gave up competitive running due to the limitations in training duration. Lastly, we present a case of 19-year-old football player, who was referred to our department due to muscle stiffness occurring at rest after brief periods of exercise. Upon continuation of the exercise, stiffness was resolved. Symptoms were not elicited by cold nor by fasting or carbohydrate loading. His past medical history was normal, and his family history was unremarkable. He had no sensory symptoms, pain, weakness or cramps. Physical examination was normal with no percussion myotonia, no muscle atrophy or hypertrophy. Blood studies, including cell count, electrolytes, chemistry panel including creatine kinase (CK) levels and thyroid testing, were all normal. On electrophysiological testing, routine nerve conduction studies were within normal limits. On needle EMG, abundant myotonic discharges were recorded from every muscle tested (Abductor Pollicis Brevis, Biceps Brachii, Tibialis Anterior) (Figure 2) and motor unit action potentials (MUAPs) were normal, with normal recruitment, with no sign of myopathic pathology. RNS at 3 Hz revealed significant amplitude decrement of CMAP in abductor policis brevis (APB) and abductor digiti minimi (ADM) (Figure 3). Based on the clinical and neurophysiological characteristics, a diagnosis of myotonia congenita was made. DNA testing is pending since the patient initially denied to do it, afraid of being banned from his football team in case of a positive result. He was treated with low doses of phenytoin and responded well. Non-dystrophic MDs are very rare disorders, but surprisingly, more cases involving athletes are described in the medical literature than in MG. In both disorders, weakness is not constant but occurs after exercise or, in the case of myotonia congenita, after rest following exercise. Besides myotonic discharges, decremental response of CMAP, either after repetitive stimulation or after short/long exercise, is described. Unfortunately, among the previously described cases, only one reports results from a 5 min exercise test, which  
Figure 3: Decremental response of CMAP after 3 Hz stimulation of ulnar nerve, recording from Abductor Digiti Minimi (ADM) muscle. Figure 2: Myotonic discharge from Abductor Pollicis Brevis (APB) muscle. was negative. Metaphorically, a short exercise test was conducted in the field, when patients were asked to run for 20 min [17] or play basketball for 20 min [15] to reproduce clinical symptoms. It is noteworthy that patients did not encounter any difficulties in everyday life. Probably, if they had not trained intensely due to their participation in competitions, the disease might not have been revealed. Supporting this is the fact that, after evaluating other family members who did not participate in sports activities, a myotonic phenotype was identified in four out of six cases. In all cases, medical treatment substantially alleviated symptoms and all six could continue with their athletic performance. Only the runner gave up competing because of training restrictions. Based on the description of these case reports, one can conclude that athletic activity, even at a competitive level, is not contraindicated in cases of MDs. Medications relieve symptoms of muscle stiffness. Furthermore, these disorders are not progressive and do not affect other organs, as is the case with dystrophic myotonias, which are associated with cardiac arrhythmias and endocrine dysregulation.