## 1 Introduction  
The coronavirus pandemic (COVID-19) has affected people around the world and strict lockdown measures have been imposed in order to counter the viral spread, resulting in increased anxiety, depression and suicidal thoughts [1]  
The respiratory syndrome caused by Coronavirus SARS-CoV-2 tends to recover completely, in most cases, in two to six weeks with molecular swab test negativization. In about 10-35% of people, however, recovery can continue with a long convalescence, referred to as post-COVID syndrome. The latter is characterized by the persistence of non-specific disabling symptoms, even for several months after infection resolution, with considerable variability among individuals [2].  
Nonspecific symptoms occur in about 50-80% of patients recovered from symptomatic COVID-19 infection [3, 4, 5]. [PERSON] et al. [6] observed that after an average of 60 days from the onset of the first COVID-19 symptom, only 12.6% of patients fully recovered; while the remaining 87.4% had persistent symptoms and 44% reported a worsening quality of life. This \"long-term carrier\" population is referred to as Long-Haulers. The exact etiological mechanism is not yet fully known, but it is believed that virus-induced immunological imbalances may be at the base [7]. The most common disorders and clinical signs reported by these patients are: muscle pain, fatigue, difficulty concentrating and air hunger. Moreover, in consideration of the numerous organs and systems involved, it can also induce pulmonary, cardiovascular, hematological, renal, gastrointestinal, dermatological, endocrine and neuropsychiatric sequelae [8].  
Most of the following, however, can be considered post-traumatic stress disorders: mood and sleep disorders, headache, asthenia, paraesthesia and diffuse musculoskeletal pain [9].  
The resolution of this syndrome represents a real challenge for doctors of different specializations and for health systems since, in the near future, it could turn into a very high expense [10].  
Studies have shown that clinical features of FM are common after symptomatic COVID-19 infection with an estimated prevalence of about 31% [6], very similar prevalence is detected with other post-COVID chronic pain disorders [11; 12].  
Approximately 30.7% of COVID-19 recovered patients meet the American College of Rheumatology criteria for FM, especially if obese and male [6; 13].  
FM is a complex disease characterized by a wide range of symptoms, notably chronic widespread pain, fatigue and sleep disturbances [14]. The pathogenesis of FM has not yet been fully understood. There is an increase and a disperception of pain associated with neuromorphological alterations and dysregulation between pro-nociceptive and anti-nociceptive pathways. A genetic predisposition has been recognized and its appearance has been associated with stressful life events, psychological characteristics and small fiber neuropathues or neuroinflammation. In addition, the role of some infectious agents, particularly of viral origin, have been hypothesized as being among the triggering factors [15].  
The use of ALC has recently been proposed in the treatment of symptoms of fibromyalgia. ALC is an endogenous molecule with an important role in energy metabolism, and, thanks to its antioxidant and brain neurotransmitter modulation properties, it has neurotrophic and analgesic activities, even in the long term, on inflammatory and chronic neuropathic pain [16].  
In relation to the clinical correlation between post-COVID syndrome and FM, the present observational case-control study aims to evaluate the effectiveness of physical exercise in association with ALC therapy, in patients with post-COVID syndrome, in terms of improvement of musculoskeletal pain, dyspnea, functional capacity, quality of life and depressive symptoms.