Balance and posture are two topics that have been extensively studied, although with some conflicting findings. Therefore, the aim of this work is to analyze the relationship between the postural angles of the spine in the sagittal plane and the stable static balance. A cross-sectional study was conducted with children and adolescents from schools in northern Portugal in 2019. An online questionnaire was used to characterize the sample and analyze back pain. Spinal postural angle assessment (pelvic, lumbar, and thoracic) was performed using the Spinal Mouse^®, while stabilometry assessment was performed using Namrol^® Podoprint^®. Statistical significance was set as α = 0.05. The results showed that girls have better balance variables. There is a weak correlation between the anthropometric variables with stabilometry variables and the postural angles. This correlation is mostly negative, except for the thoracic spine with anthropometric variables and the lumbar spine with BMI. The results showed that postural angles of the spine are poor predictors of the stabilometric variables. Concerning back pain, increasing the postural angle of the thoracic spine increases the odds ratio of manifestation of back pain by 3%.

Purpose: Back pain is a growing problem worldwide, not only in adults but also in children. Therefore, it is becoming increasingly important to investigate and understand the factors that influence the early onset of back pain. The aim of this study was to determine the prevalence of back pain in children and adolescents and to identify predisposing risk factors and protective factors. Methods: A cross-sectional study was conducted between October and December 2019 in schools from northern Portugal, evaluating 1463 students aged 9 to 19 years, of both genders. The instruments used were the Spinal Mouse® to assess posture, the Inbody 230® to assess body composition, an online questionnaire to characterize the sample and back pain, and the FITescola® battery test to access physical fitness. Results: Half of the subjects experienced back pain at least once in their lifetime. The most frequently mentioned were lumbar spine and thoracic spine, mostly with mild or moderate pain intensities. Age, female gender, percent body fat, prolonged smartphone and computer use, hyperkyphosis, and the lateral global spine tilt to the left side are all factors with higher relative risk of back pain. Practicing physical activity or sports regularly and video games have a protective effect. Conclusion: The prevalence of back pain in children and adolescents is very high: The study enhances the case for protective factors such as physical activity habits or video games while reinforcing risk factors such as percent body fat, prolonged smartphone or computer use, and posture.

Human pain is a complex and multifaceted phenomenon(1) that is controlled by multiple systems in the human body (2). These systems work together to process, interpret and respond to pain (3).The International Association for the Study of Pain defines pain as "an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage" (4) This experience evokes an integrated response from the various systems associated with pain.This integrated response to the phenomenon of pain occurs in a more complex way at the level of the cortex where pain is consciously perceived, such as the primary somatosensory cortex, the primary motor cortex and supplementary motor cortex, the secondary somatosensory cortex, the insular cortex, the anterior cingulate cortex and the thalamus (5,6). Also at an unconscious level, but more central, is the emotional regulation of pain, which is linked to the limbic system, where the experience of pain acquires an individual component linked to the emotions and experiences of the individual themselves, such as memory and fear in the amygdala, hippocampus and subcortical structures, including the basal ganglia (6,7).In addition, there are some systems that are particularly important in pain regulation, namely the immunological system, the endocrine system and the descending noradrenergic system. Despite today's deeper understanding of pain mechanisms, there is still a lack of solutions for more complex conditions. The role of the autonomic nervous system (ANS) in pain modulation with the different systems involved in pain, such as the immunological system, the endocrine system and the descending noradrenergic system, is becoming increasingly clear and there is an urgent need to develop solutions for effective modulation of the ANS with a focus on pain (9). From this perspective, neuromodulation of the ANS appears to be a potentially supportive solution for the modulation of pain, in particular non-invasive neuromodulation of the autonomic nervous system NESA, which has been shown to be effective for pain in chronic pathologies such as multiple sclerosis (8).The need arises for effective non-pharmacological treatments, based on electrical neuromodulation, and backed by scientific evidence to support their use for pain. In this sense, previous studies have shown that microcurrent technologies for prefrontal and primary motor cortex modulation such as transcranial stimulation (tDCS) combined with peripheral stimulation (9) or vagal stimulators (VNS) (10) have demonstrated benefits on different aspects of pain, headaches, chronic pain in diverse populations (11). However, science is advancing and other types of specific microcurrent are emerging for autonomic modulation targets that are more comfortable for the patient, with no side effects and an easier application, such as non-invasive neuromodulation NESA (12). It is therefore necessary to explore the field of work of NESA microcurrents so that they can be used to modulate pain through the autonomic nervous system.Subsections relevant for the subject.The immune system influences the release of substances such as pro-inflammatory cytokines, which sensitize pain receptors and pathways and thus increase the perception of pain (13). The immune system also plays a role in reducing pain levels in the process of tissue recovery (14). The regulation of the immune system, pain and inflammation is largely mediated by the ANS and its different divisions such as the sympathetic, parasympathetic and enteric branches (15). This deregulation can be observed in autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus and multiple sclerosis, where changes in the ANS are associated with increased inflammation. As a result of these increased inflammatory levels, there is a dysfunctional interaction between the ANS and the gut microbiota with direct effects on the homeostasis of inflammation (14,15). A study with individuals with rheumatoid arthritis showed a strong correlation between the increase in sympathetic activity due to muscle sympathetic nerve activity and the painful symptoms of these patients (16).The endocrine system also has an influence on pain regulation via hormones that influence pain perception (17,18). The hypothalamic-pituitary-adrenal axis (HPA axis) and cortisol is an important hormonal regulatory system that is also of great importance for the regulation of pain by regulating cortisol levels. Elevated cortisol levels following acute stress can facilitate the consolidation of fearbased emotional memories and cause a sensitized physiological response to stress. However, prolonged stress or situations of constant or exaggerated physical pain can increase sympathetic and neuroendocrine activity, decrease cortisol levels, and perpetuate generalized pain and inflammation (19). The increase in cortisol levels is accompanied by an increase in adrenaline levels associated with acute pain or stress, which can transiently alter pain perception (14). This type of response is often associated with the "fight or flight" response, which can temporarily reduce pain sensitivity (20). However, prolonged chronic stress leads to a functional change in the ANS that impairs pain regulation, such as in fibromyalgia (21,22) and central sensitization (23).Pain modulation also depends on an important system such as the descending noradrenergic system, its relationship with the periaqueductal gray matter (PAG) and the reticular formation of the brainstem (24). The PAG is also involved in risk assessment and threat response and contributes to defensive behaviors related to negative events. These pathways lead to learned aversive behaviors through the involvement of sympathetic responses, motor responses, and emotional responses characteristic of acute and chronic pain (25). Some structures are particularly important for the development and maintenance of...

This paper introduces and implements a method to monitor muscle fatigue in real-time using a wearable biofeedback system to improve muscle rehabilitation treatments. The biofeedback system consists of an electromyography (EMG) sensor to capture muscle activity and two motion sensors to track knee angles. The proposed method for monitoring muscle fatigue involves three steps: (1) recognition of the movement phases during the knee extension exercise; (2) clipping of the EMG signal and calculation of fatigue-related metrics; and (3) normalization of metrics through a calibration process. An experimental session was performed with 10 healthy subjects performing 50 repetitions of the knee extension exercise. Processed data revealed changes in fatigue-related metrics, which align with existing literature. A comparison was also made between real-time and computer processing using raw data. While minor differences were noted between the two processing methods, the mobile app closely mirrored the trajectory of processed data in the cloud, ensuring reliability and consistency. This study advances remote muscle rehabilitation by quantifying muscle fatigue during treatment sessions. Thus, health professionals can tailor treatment plans based on individual patient characteristics, optimizing treatment duration, and reducing injury risk.