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EN
Purpose. Postural control during quiet standing has been modeled by concepts using kinematic variables estimated from center of pressure (COP) signals. The concept of position-based postural control has had particular ramifications in the literature, although a more recent concept of velocity-based control has been proposed as being more relevant. Methods. This study reviews the literature investigating these concepts and their respective quantitative methods alongside current supporting evidence and criticisms. Results. The position-based control concept suggests the existence of two control loops that alternate whenever certain thresholds are exceeded. Such a theory is supported by studies describing the time delay between the skeletal muscle activation and CoP displacement. However, this concept has been criticized to be the result of statistical artifacts due to it not being adapted to the analysis of bounded time series. Conversely, the velocity-based control concept claims that velocity is the most relevant kinematic variable for postural control. Such a theory suggests that postural adjustments are executed to change the trajectory of the CoP whenever the velocity crosses a threshold. Both theories have their major methodological limitations, while interpretation of data from the position-based concept is difficult, velocity-based thresholds are empirical and still need verification in different motor tasks and populations. Conclusions. Given the observed similarities and mutual exclusivity of both concepts, there is a need for the development of methods that can quantitatively analyze stabilometric signals while simultaneously considering both kinematic variables.
EN
Purpose. The purpose of this study was to evaluate the effects of short-term perturbation-based balance training and a detraining period on postural control in older adults. Methods. A group of healthy older women were recruited and divided into two groups: an exercise group (EG, n = 21, age = 67.0 ± 2.0 y) that performed balance-based exercises three times a week over a sixweek period and a control group (CG, n = 20, age = 67.9 ± 3.1 y). Center-of-pressure displacement (CoP) and electromyographic data (EMG onset, time-to-peak and amplitude) were assessed during forward and backward perturbations for six leg muscles. All variables were analyzed before the training program began, at its end, and after a six-week period of detraining. A mixed ANOVA model was used to analyze the within- and between-subject results. Results. A decrease in backward CoP displacement, EMG onset and time-to-peak of the ankle muscles, especially the tibialis anterior (TA) and gastrocnemius (MG), was observed. Improvement in muscle EMG amplitude for the ankle muscles (TA, MG and Soleus - SO) at the early phase (0-200 ms) of the perturbation test, with the SO also showing an increase in amplitude at the intermediate phase (201-400 ms). After the detraining period, only the TA muscle maintained an improvement in reaction time. Conclusions. Perturbation-based balance training improved neuromuscular responses such as muscle reaction time and ankle muscle activation and consequently aided the body’s ability to maintain correct center of pressure, although after a period of detraining this gain was not maintained for most of the assessed variables.
EN
The present study aimed at investigating the control of upright quiet standing in pregnant women throughout pregnancy, and whether low-back pain exerts influence on this motor task. Methods: Myoelectric signals from postural muscles and stabilometric data were collected from 15 non-pregnant and 15 pregnant women during upright quiet standing. Electromyogram envelopes and center of pressure metrics were evaluated in the control group, as well as in pregnant women in their first and third trimester of pregnancy. A correlation analysis was performed between the measured variables and a low-back pain disability index. Results: Pregnant women exhibited a decreased maximum voluntary isometric activity for all postural muscles evaluated. Additionally, the activity of lumbar muscles during the postural task was significantly higher in the pregnant women in comparison to the non-pregnant controls. The soleus muscle maintained its activity at the same level as the gestation progressed. Higher postural oscillations were observed in the anteroposterior direction while mediolateral sway was reduced in the third trimester of pregnancy. No correlation was detected between the lowback pain disability index and neuromechanical variables. Conclusion: This study provides additional data regarding the functioning and adaptations of the postural control system during pregnancy. Also, we provide further evidence that postural control during quiet standing cannot be used to predict the occurrence of low-back pain. We hypothesize that the modifications in the neural drive to the muscles, as well as in postural sway may be related to changes in the biomechanics and hormonal levels experienced by the pregnant women.
EN
Purpose: The aim of the study was to determine whether 10- to 13-year-old, national-level, female acrobatic gymnasts present a different quiet standing postural control (with and without visual cues) than untrained female peers. Methods: The mean velocity of the center of pressure (in anterior-posterior and medial-lateral directions) was computed from 60-s long quiet-standing trials on a stationary force plate in fifteen 10- to 13-year-old female acrobatic gymnasts and thirteen sex- and age-matched non-athletes. A two-way repeated measures ANOVA (acrobatic gymnasts vs. non-athletes and eyes open vs. eyes closed) was used for the anterior-posterior and mediallateral COP mean velocity. The relation between subjects’ body mass and COP mean velocity was tested with the used Spearman’s Rank Correlation Coefficient. Results: Postural sway (represented by COP mean velocity) was not significantly different between the acrobatic gymnasts and the non-athletes ( p > 0.05), except for the faster medial-lateral sway in eyes-open conditions in the acrobatic gymnasts ( p < 0.05). The gymnasts’ body mass negatively correlated with their anterior-posterior sway velocity in both visual conditions (eyes open: r = –0.7; eyes closed: r = –0.6) and with medial-lateral sway velocity during eyes-closed trials (r = –0.5; p < 0.05). Conclusions: Results of the study indicate that in quiet standing postural control 10- to 13-year-old acrobatic gymnasts did not make use of their trained abilities. Heavier gymnasts might have been more stable than lighter ones during quiet standing.
EN
Introduction: Structural stability assess of the impact of the sense of the reactions equivalent. The aim of this study was to determine the importance of maintaining control patterns in static equilibrium of women after mastectomy. Materials and methods: The study included 150 women. In the first group there were 75 women after mastectomy, mean age 60 (±7,6), mean BMI 26 (±3,6). In the control group there were 75 age matched women (59 (±6,5), BMI 26 (±7,9) without a history of cancer diseases. The study was conducted using a tensometric platform. Quantification was composed of two 30-second test, the first test with eyes open and a second after 5-10 second pause with eyes closed. Results: It was found that there were significant statistical differences within a significant part of the measured parameters with eyes closed, and for all the Romberg parameters. There were: COP (centre of pressure) path length (p = 0.0411), the COP path length measured in the anterior-posterior direction (p = 0.0251), the average tilt COP (p = 0.0025), the maximum swing in the x-axis (relating to the range lateral stability) (p = 0.0447). In addition, there were statistically significant differences between the parameters: the average speed of a moving 2D COP (p = 0.0432) and the y-axis (p = 0.0240). Conclusion: Balance after mastectomy was less dependent on the vision than in the control group. Physiotherapy program after mastectomy should include proprioceptive training, with closed eyes to improve the equilibrium reaction quality and increase the postural stability.
EN
This manuscript presents an overview of current knowledge on the influence of organic solvents on the hearing and balance systems. The authors analyzed - the literature data concerning the results of all human and the most relevant animal studies, published untill 2012. Moreover, the guidelines for occupational medicine specialists were proposed on the basis of literature review and the authors' own scientific experience. The literature data and our studies revealed the increased risk of hearing loss in workers exposed to organic solvents only, and well documented potentiation of harmful effects of combinedexposure to organic solvents and noise. Hearing impairment is mainly observed in high frequencies, but lower frequencies can also be involved (0.5-4 kHz). The impairment induced by exposure to organic solvents is mild, up to several dBs. In the combined exposure to noise and solvents , the noise effect predominates. Organic solvents affect the central pathways of vestibular system although unilateral or bilateral vestibular hypofunction might also be a possible consequence of solvent exposure. Occupational exposure to organic solvents is a risk factor for hearing and balance impairments. Therefore, workers exposed to solvents should be covered by hearing loss prevention programs. Speech in noise test (HINT) and posturography seem to be the most suitable tests for hearing and balance prevention programme for organic solvent exposed workers. Med Pr 2013;64(1):83–102
PL
Publikacja podsumowuje stan aktualnej wiedzy na temat ototoksycznego wpływu rozpuszczalników organicznych na narząd słuchu i układ równowagi. Przegląd danych literaturowych obejmuje wszystkie istotne badania u ludzi oraz najważniejsze badania na zwierzętach zawarte w bazie PubMed do połowy roku 2012. Ponadto w pracy przedstawiono zalecenia dla celów profilaktyki medycznej opracowane w oparciu o dane literaturowe i badania własne. Wyniki badań, w tym opublikowanych badań własnych, wykazały, że głębokość uszkodzenia słuchu przypisywana narażeniom na te substancje chemiczne może wynosić kilka, kilkanaście dB HL. Uszkodzenia słuchu obserwowano głównie w zakresie wysokich częstotliwości, choć mogą dotyczyć również częstotliwości średnich (0,5-4 kHz). Przy łącznym działaniu rozpuszczalników i hałasu dominuje efekt hałasu. Udokumentowany jest również wpływ rozpuszczalników organicznych na ośrodkową część układu równowagi oraz niewykluczony - na część obwodową (błędnik). Wynikiem uszkodzenia jest zmniejszenie pobudliwości układu przedsionkowego czy asymetria pobudliwości. Mimo że nie jest znana zależność typu dawka-odpowiedź, wyniki dotychczasowych badań wskazują na konieczność objęcia osób narażonych na rozpuszczalniki organiczne badaniami profilaktycznymi pod kątem wykrywania zaburzeń narządu słuchu i równowagi. Podstawowymi badaniami w tym zakresie powinny być, oprócz konsultacji laryngologa/audiologa, badania audiometrii mowy w szumie (hearing in noise test - HINT) oraz posturografii. Med. Pr. 2013;64(1):83–102
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