The observation of persons in the acute phase of ischemic stroke (IS) during the period from the beginning of hospitalization to the moment of standing up to vertical positions allowed to select a group of persons whose spontaneous motor activity stood out from the typical clinical picture of the hemiplegia syndrome. It has been noticed that persons from this group have tendency to shift the body weight toward more affected side (MAS) in sitting which makes it more difficult for them to develop a stable upright position. An additional symptom noticed in these persons, that makes the re-education of postural function difficult, was the tendency to move the less affected upper extremity (LAUE) and/or the less affected lower extremity (LALE) – not covered by the neurological syndrome. These motor behaviors were also observed in the supine at the beginning of the persons' hospitalization. An additional interesting symptom presented by these persons was typical asymmetry in supine. Aims of this study were to describe and characterize the phenomenon of overactivity of less affected side (OLAS) in persons with acute IS and to creative a predictive model for the occurrence of OLAS.

The study group consists of persons suffered from first-time IS confirmed in MRI or TC. Persons with focal injury in the thalamus or/and cerebellum with another neurological disease in persons’ history and with loss of conscious incident during hospitalization were excluded from the observation. The research was carried out in the years 2020-2021 at the Department of Neurology, Faculty of Medicine and Dentistry, Medical University of Warsaw, located at the Bielański Hospital. The research process collected data from 125 women (56%) and 97 men (44%). The average age of the persons was 71.82 ± 14.27 years and ranged from 29 to 99 years. Persons with first-time IS, on the first day of the physiotherapeutic evaluation were divided into 3 groups depending on their symptoms – Figure 1.

According to the study design none of the persons from the group A – Table 1. – had finally presented OLAS and they were excluded from the further analysis. These persons have suffered from a mild neurological syndrome, so further analysis comparing persons with and without OLAS could generate overestimated differences between them.

Observation of persons in the acute IS in the period from the beginning of hospitalization to the moment of sitting and standing, allowed to select a group of persons whose spontaneous motor activity stood out in comparison to people presenting a typical clinical picture of hemiplegia. Based on the results of this research inspired by the observation of the clinical condition of people in the acute phase of IS, the concept of OLAS was defined. In addition, the most typical symptoms of OLAS were characterized, and it was determined which neurological symptoms coexist with it. It was considered whether, in view of the above, the characteristic motor behaviors observed in persons on the first day of physiotherapeutic assessment could be predictive symptoms for later therapeutic problems in higher positions? To the best of the researchers' knowledge, no work has yet been published with such an approach to the problem of persons in the acute phase of IS.

It was hypothesized that the group of persons presenting baseline symptoms of OLAS (additional movements of the LAE and/or AiS) would be the group that would also be characterized by asymmetry in high positions, and thus – based on observation of the supine position only will allow the diagnosis of OLAS to be made. The results on the motor symptoms of OLAS collected from the analysis at the beginning of hospitalization showed that each symptom typical of OLAS from the index day, analyzed separately, was a significant predictor of the occurrence of OLAS in sitting. An attempt was also made to create a predictive model from more than one typical symptom of OLAS from the index day to check whether adding one significant symptom to another would improve the ability to predict that OLAS would actually occur in the sitting position. The conducted analysis gave the results that the coexistence of LAUE and LALE activity on the first day of physiotherapeutic assessment allows, with a certain probability, to predict the occurrence of OLAS in sitting. A review of the literature on the treatment of people with IS did not provide data with which the obtained result could be compared.

One of the hypotheses was the occurrence of characteristic, reproducible differences in the sitting between persons with OLAS and people with a typical clinical picture of post-stroke hemiplegia. It was noticed that persons from OLAS group have tendency to shift the body weight to MAS, which makes it more difficult for them to develop a stable sitting position, and then - standing. In addition, in the sitting, persons also tended to move their LAE. To check the validity of this hypothesis, the way persons with OLAS presented themselves in a sitting position was examined. It was checked which behaviors in this position appear most often and whether the selected variants of motor behaviors are significantly different from others. Such action was needed to create the definition of OLAS. Of all the symptoms of OLAS in sitting presented by persons, three variants of motor behavior stand out from the statistical point of view. OLAS in the sitting position may be manifested not only by asymmetry of the trunk with a deviation towards MAS. The coexistence of a tendency to move the LAE is also important. Information has been found in the literature on the existence of other possible causes of sitting instability. These include, for example, antigravity muscles weakness, changes in muscle tone, hemineglect, or Pusher Syndrome – PS which, apart from extension and abduction activity of the limbs on the LAS and passive resistance during posture correction, is characterized by tilting to the MAS. However, this is due to a specific reason – such persons incorrectly perceive the position of their body in the frontal plane, defining their position as correct (symmetrical) when it is tilted by 18-20 degrees to the MAS. PS persons (similar to OLAS persons) demonstrate abnormal activity of the LAS, and limited ability to change movement patterns. The clinical Scale for contraversive pushing, in which the occurrence of the mentioned symptoms is evaluated (in contrast to OLAS) solely in the sitting and standing positions, as well as the presence of a lesion in the thalamus as a structural cause of PS mentioned in some sources, indicate the necessity to differentiate between OLAS and PS [3,4]. In this study, to ensure that PS was not the cause of sitting asymmetry, persons with a thalamic stroke were excluded from the research. Both OLAS and PS persons tend to shift body weight to the MAS. In persons with PS, pushing activity of LAE typically leads to a fall on the MAS. In PS, the purpose of this behavior is to align the body relative to the vertical midline incorrectly perceived by patient. On the other hand, in OLAS it is probably (as researchers conclude from their clinical practice) due to the patient's feelings – it is more comfortable for the patient to take the weight off the LAS, which is indicated by protesting motor behavior in the situation of hypercorrection and support on the LAE, e.g. in sitting. It should be emphasized, however, that persons with OLAS will allow for positioning to the support on the LAS during therapy, which is much more difficult to achieve in the case of persons with PS. Persons with PS, when trying to hypercorrect to the LAS, react with strong resistance. In the treatment of a patient with the PS, many vertical reference points are needed, while in the case of OLAS, therapeutic activities focus on its extinction by stimulating weighting on the LAS.

Apart from the already mentioned PS, asymmetry in the sitting position may also be caused by weakening of the muscular strength of the limbs and trunk, decreased muscle tone, disorders of superficial and deep sensation, cerebellar syndrome and hemineglect [5,6,7,8,9]. Among the assessed neurological symptoms in persons qualified for this study, there were many missing data caused by the lack of the verbal-logical contact with the patient which is necessary to conduct a full neurological examination. For this reason, superficial and deep sensation, or the presence of hemineglect, was impossible to assess in some cases. It is noteworthy that the group of persons diagnosed with OLAS consisted of persons with a significant severity of the neurological syndrome, similar to PS. Statistical analysis of data collected from persons in the second measurement period confirmed that persons with OLAS significantly more often suffered from decreased muscle tone in more affected lower and upper extremity severe paresis or paralysis of the limbs, sensory disturbances, and hemineglect. Therefore, it was considered whether the asymmetry occurring in OLAS may be caused by the above-mentioned disorders, or is even the result of several of them. A similar asymmetry to that observed in OLAS may be presented by persons with deficits in superficial and deep sensation, hemineglect and more severe hemiparesis. Exactly the same symptoms appear to be significantly associated with the behavior of persons with OLAS. However from the available literature, it can be learned that with such disorders, typical asymmetry (with a greater load on the MAS) is possible, however, it occurs less frequently than the opposite pattern - with the body weight shifted the LAS. This would suggest that OLAS is a separate cause of sitting asymmetry. However, it cannot be ruled out that mentioned disorders underlie the behavior of persons in OLAS.

At the stage of study designing, it was hypothesized that persons with OLAS symptoms from the first and second measurement time would also present symptoms of overactivity in the standing. In the standing data were collected from 37% of persons with OLAS. An interesting observation is that 4 persons (9.8%) showed signs of OLAS (strong transfer of body weight to the MAS and inability to weight more affected lower extremity) only in the standing. The data collected from the persons did not show a significant relationship between the occurrence of OLAS in the sitting and the pattern of weighting more affected lower extremity in the standing. This result indicates that persons diagnosed with OLAS in the sitting do not necessarily have problems in the standing. On the other hand, it cannot be said that persons with or without OLAS in sitting will not show the symptoms of OLAS in standing. An issue that requires comment is also the time when it was decided to facilitate the patient to standing position. From the physiotherapy’s point of view persons in the acute IS, before facilitating the standing position, should first regain stability in the sitting. As mentioned earlier, OLAS persons present the problem of trunk instability in sitting. It has been shown that persons with OLAS needed more time to be able to stand correctly and independently.

In purely theoretical terms, it is unclear whether the observed motor activities of the LAE in subjects with OLAS correspond with the hemispheric activity visible on fMRI. According to literature, moving the more affected upper extremity during the acute phase of stroke triggers pathological stimulation in both hemispheres of the brain, while moving the less affected extremity does not have the same effect [10]. Could the continuous, repetitive movement of LAE, which patients exhibited during their initial physiotherapy assessments, be directed towards "protecting" the damaged hemisphere in the event of significant damage? This study does not provide the researchers with the means to answer this question. However, the mechanism of activation of the brain hemispheres after an ischemic stroke was considered when reflecting on physiotherapy methods. It was noted that movement of the more affected limbs induces pathological stimulation of both brain hemispheres, whereas movement of the less affected extremities (LAE) does not. Scientific reports provide information on physiotherapeutic interventions aimed at determining the impact of such activities on interhemispheric balance. In 2021, N. Salehi et al. published research attempting to answer whether increasing resistance exercises performed by LAUE could restore balance of interhemispheric activity visible in fMRI. Additionally, the study aimed to determine if patients undergoing this therapy would experience greater improvements in the motor functions of their more affected upper extremities compared to patients undergoing standard therapy. The study group exhibited a markedly greater enhancement in muscle strength and efficiency in comparison to the control group. The researchers identified improved interhemispheric balance as the mechanism responsible for enhancing strength in the more affected upper extremity [11]. It is remarkable that the use of the LAS does not induce any pathological pattern of interhemispheric activity and promotes proper activation, which is encouraging.

In this research it has been assumed that TT is a useful tool in the process of diagnosing OLAS. Persons reacting positively to this therapeutic intervention were diagnosed as OLAS. In everyday physiotherapeutic practice and in the functional diagnostics of each patient – also a patient after a stroke – trial therapy should be used as a tool for programming an individual rehabilitation process. It allows to assess whether the given techniques are acceptable by the patient, constitute a movement challenge at an appropriate level of difficulty for him. Trial therapy is also a valuable element of the rehabilitation program evaluation. The main therapeutic rule based on neurophysiological schools is to reduce asymmetry by shifting weight on the LAS. For the purposes of this study, the TT could be performed when the patient was able to actively, with little help, maintain a sitting position. The therapy was conducted on the patient's bed. In this study, the TT was constructed on the theoretical knowledge, own observations and experience of working with persons. It has not been evaluated for effectiveness. Further analysis is required for a better understanding of OLAS. One of the stages of expanding knowledge about OLAS may be an attempt to modify the trial therapy, also in terms of its impact on overactivity observed in the supine.

The study results allows to present the OLAS definition as instability of the trunk in the sitting position with associated characteristic motor activities of less affected limbs. Moreover, predictive symptoms of OLAS were distinguished.