Anticipatory control of head posture.

OBJECTIVE: We tested a hypothesis on two patterns of anticipatory postural adjustments (APAs) in neck muscles, reciprocal and co-activation, that may be used in a task-specific way. We also explored possible relation of APAs in leg and trunk muscles to head stabilization. METHODS: Load perturbations (loading and unloading) were applied to the head, trunk, and head and trunk simultaneously using similar hand actions by standing persons. Electromyographic signals (EMGs) from 10 muscles were recorded. Shifts of the center of pressure and EMG indices were computed over typical time intervals for APA. RESULTS: Time-shifted (reciprocal) activation of neck flexor and extensor muscles during APAs was seen when perturbations were applied directly to the head. Simultaneous activation dominated when the perturbations were applied to the trunk. Minimal APAs were seen in the leg/trunk muscles during head perturbation tests. APAs during trunk perturbation were not different from those during trunk and head perturbation. CONCLUSIONS: The results confirm the existence of two different patterns of APAs in neck muscles. A time-shifted (reciprocal) pattern is more likely to be used in anticipation of a perturbation acting directly on the head. A simultaneous activation (co-activation) pattern is used when direction of head perturbation cannot be predicted with certainty. Leg/trunk APAs are unlikely to help stabilize head posture. SIGNIFICANCE: These results are important for better understanding of feed-forward mechanisms of the control of head posture with possible implications for neurological patients who suffer from impaired feed-forward postural control.     

Multi-muscle control during bipedal stance: an EMG–EMG analysis approach

Posture and postural reactions to mechanical perturbations require the harmonic modulation of the activity of multiple muscles. This precision can become suboptimal in the presence of neuromuscular disorders and result in higher fall risk and associated levels of comorbidity. This study was designed to investigate neurophysiological principles related to the generation and distribution of inputs to skeletal muscles previously recognized as a synergistic group. Specifically, we investigated the current hypothesis that correlated neural inputs, as measured by intermuscular coherence, are the mechanism used by the central nervous system to coordinate the formation of postural muscle synergies. This hypothesis was investigated by analyzing the strength and distribution of correlated neural inputs to postural muscles during the execution of a quiet stance task. Nine participants, 4 females and 5 males, mean age 29.2 years old (±6.1 SD), performed the task of standing while holding a 5-kg barbell in front of their bodies at chest level. Subjects were asked to maintain a standing position for 10 s while the activity of three postural muscles was recorded by surface electrodes: soleus (SOL), biceps femoris (BF), and lumbar erector spinae (ERE). EMG–EMG coherence was estimated for three muscle pairs (SOL/BF, SOL/ERE, and BF/ERE). Our choice of studying these muscles was made based on the fact that they have been reported as components of a functional (synergistic) muscle group that emerges during the execution of bipedal stance. In addition, an isometric contraction can be easily induced in this muscle group by simply adding a weight to the body’s anterior aspect. The experimental condition elicited a significant increase in muscle activation levels for all three muscles (p < 0.01 for all muscles). EMG–EMG coherence analysis revealed significant coherence within two distinct frequency bands, 0–5 and 5–20 Hz. Significant coherence within the later frequency band was also found to be significantly uniformly distributed across the three muscle pairs. These findings are interpreted as corroborative with the idea of a hierarchic system of control where the controller may use the generation of common neural inputs to reduce the number of variables it manipulates.     

Prevalence of minor psychiatric disorders among primary healthcare workers in the South and Northeast regions of Brazil

Mental health problems are among the most prevalent conditions in health workers. We evaluated the prevalence of minor psychiatric disorders and associated factors among primary healthcare workers. The study design was cross-sectional and services-based, in 240 primary healthcare units in 41 municipalities (counties) with more than 100 thousand inhabitants in seven States in the South and Northeast regions of Brazil. A total of 4,749 primary healthcare workers were interviewed, and prevalence of minor psychiatric disorders was 16%, with no statistical differences according to region or primary care model. The rate was higher in community health workers and other workers with secondary education (18%) and lower in health professionals with university training (10%); while physicians (15%) and nurses and nurse technicians (14.6%) were in an intermediate situation (p < 0.001). Occupational characteristics showed the strongest association with the occurrence of minor psychiatric disorders according to the adjusted analysis, suggesting that their reduction requires improvements in work conditions in primary healthcare and in the management of the Unified National Health System.     

Evaluation of the effectiveness of Primary Health Care in South and Northeast Brazil: methodological contributions

The article presents the methodology used in the Baseline Study that evaluated the effectiveness of the Family Health Strategy as compared to traditional primary health care units. The study included 41 municipalities with more than 100 thousand inhabitants each, 21 from the South and 20 from the Northeast of Brazil. As the principal dependent variable and underlying premise for sampling in the Baseline Study, the effectiveness of program activities in the primary care units was analyzed in the population within the respective coverage areas, using an epidemiological survey. The health care model in the primary care units was the principal independent variable. Its effect on program activities was controlled according to geopolitical region, metropolitan area, and population size in the municipalities. Coverage of the activities was characterized according to socioeconomic, demographic, and health-related factors. The use of comparison groups, multiple-stage samples, standardized measures, adjustment for geographic and socio-demographic characteristics, and well-defined criteria for judging the findings are contributions by the methodology employed here for designing future studies to evaluate primary health care.     

Postural control during upper body locomotor-like movements: similar synergies based on dissimilar muscle modes

We studied the organization of leg and trunk muscles into groups (M-modes) and co-variation of M-mode involvement (M-mode synergies) during whole-body tasks associated with large variations of the moment of force about the vertical body axis. Our major questions were: (1) can muscle activation patterns during such tasks be described with a few M-modes common across tasks and subjects? (2) do these modes form the basis for synergies stabilizing M _z time pattern? (3) will this organization differ between an explicit body-rotation task and a task associated with locomotor-like alternating arm movements? Healthy subjects stood barefoot on the force platform and performed two motor tasks while paced by the metronome at 0.7, 1.0, and 1.4 Hz: cyclic rotation of the upper body about the vertical body axis (body-rotation task), and alternating rhythmic arm movements imitating those during running or quick walking (arm-movement task). Principal component analysis was used to identify three M-modes within the space of integrated indices of muscle activity. The M-mode vectors showed clustering neither across subjects nor across frequencies. Variance in the M-mode space across sway cycles was partitioned into two components, one that did not affect the average value of M _z shift (“good variance”) and the other that did. An index was computed reflecting the relative amount of the “good variance”; positive values of this index have been interpreted as reflecting a multi-M-mode synergy stabilizing the M _z trajectory. On average, the index was positive for both tasks and across all frequencies studied. However, the magnitude of the index was smaller for the intermediate frequency (1 Hz). The results show that the organization of muscles into groups during relatively complex whole-body tasks can differ significantly across both task variations and subjects. Nevertheless, the central nervous system seems to be able to build M _z stabilizing synergies based on different sets of M-modes, within the approach accepted in this study. The drop in the synergy index at the frequency of 1 Hz, which was close to the preferred movement frequency, may be interpreted as corroborating the neural origin of the M-mode co-variation.     

Multi-muscle synergies in a dual postural task: evidence for the principle of superposition

We used the framework of the uncontrolled manifold hypothesis to quantify multi-muscle synergies stabilizing the moment of force about the frontal axis (M _Y) and the shear force in the anterior–posterior direction (F _X) during voluntary body sway performed by standing subjects. We tested a hypothesis whether the controller could stabilize both M _Y and F _X at the same time when the task and the visual feedback was provided only on one of the variables (M _Y). Healthy young subjects performed voluntary body sway in the anterior–posterior direction while different loads were attached at the ankle level producing horizontal forces acting forward or backwards. Principal component analysis was used to identify three M-modes within the space of integrated indices of muscle activation. Variance in the M-mode space across sway cycles was partitioned into two components, one that did not affect a selected performance variable (M _Y or F _X) and the other that did. Under all loading conditions and for each performance variable, a higher value for the former variance component was found. We interpret these results as reflections of two multi-M-mode synergies stabilizing both F _X and M _Y. The indices of synergies were modulated within the sway cycle; both performance variables were better stabilized when the body moved forward than when it moved backward. The results show that the controller can use a set of three elemental variables (M-modes) to stabilize two performance variables at the same time. No negative interference was seen between the synergy indices computed for the two performance variables supporting the principle of superposition with respect to multi-muscle postural control.     

Flexible muscle modes and synergies in challenging whole-body tasks

We used the idea of hierarchical control to study multi-muscle synergies during a whole-body sway task performed by a standing person. Within this view, at the lower level of the hierarchy, muscles are united into groups (M-modes). At the higher level, gains at the M-modes are co-varied by the controller in a task-specific way to ensure low variability of important physical variables. In particular, we hypothesized that (1) the composition of M-modes could adjust and (2) an index of M-mode co-variation would become weaker in more challenging conditions. Subjects were required to perform a whole-body sway at 0.5 Hz paced by a metronome. They performed the task with eyes open and closed, while standing on both feet or on one foot only, with and without vibration applied to the Achilles tendons. Integrated indices of muscle activation were subjected to principal component analysis to identify M-modes. An increase in the task complexity led to an increase in the number of principal components that contained significantly loaded indices of muscle activation from 3 to 5. Hence, in more challenging tasks, the controller manipulated a larger number of variables. Multiple regression analysis was used to define the Jacobian of the system mapping small changes in M-mode gains onto shifts of the center of pressure (COP) in the anterior–posterior direction. Further, the variance in the M-mode space across sway cycles was partitioned into two components, one that did not affect an average across cycles COP coordinate and the other that did (good and bad variance, respectively). Under all conditions, the subjects showed substantially more good variance than bad variance interpreted as a multi-M-mode synergy stabilizing the COP trajectory. An index of the strength of the synergy was comparable across all conditions, and there was no modulation of this index over the sway cycle. Hence, our first hypothesis that the composition of M-modes could adjust under challenging conditions has been confirmed while the second hypothesis stating that the index of M-mode co-variation would become weaker in more challenging conditions has been falsified. We interpret the observations as suggesting that adjustments at the lower level of the hierarchy—in the M-mode composition—allowed the subjects to maintain a comparable level of stabilization of the COP trajectory in more challenging tasks. The findings support the (at least) two-level hierarchical control scheme of whole-body movements.     

Software program to systematize data for planning public health actions

OBJECTIVE: To describe and evaluate a software program to provide basic health care teams with primary health services data. METHODS: It was described the PACOTAPS (software program for primary health care), developed using Visual Basic 5.0, and secondary data and outpatient care demand modules were tested in a basic health care unit in Pelotas, Brazil. Age/gender structure of the reference population was obtained from secondary data. Outpatient care demand allowed the characterization of all 4,170 visits carried out in a month by analyzing Outpatient Care Files. RESULTS: Age and gender distribution as well as main diagnoses and referrals were identified for all patients seen at the health care unit. In addition, there were detected differences among the health care centers due to either different organization and care models or as a result of different actual needs of improvement in patient register systems. CONCLUSIONS: PACOTAPS, a user-friendly software program, can contribute to health care unit management evaluation within the national Unified Health System (SUS). The availability of an electronic tool combining resources allows decision making in healthcare facilities, and even at municipal health policy level, to be based on more adequate and effective data.     

Muscle modes and synergies during voluntary body sway

We studied the coordination of muscle activity during voluntary body sway performed by human subjects at different frequencies. Subjects stood on the force platform and performed cyclic shifts of the center of pressure (COP) while being paced by the metronome. A major question was: does the makeup of muscle synergies and their ability to assure reproducible sway trajectory vary with the speed of the sway? Principal component analysis was used to identify three muscle groups (M-modes) within the space of integrated indices of muscle activity. M-mode vectors were similar across both subjects and sway frequencies. There were also similar relations between changes in the magnitudes of all three M-modes and COP shifts (the Jacobians) across the sway frequencies. Variance in the M-mode space across sway cycles was partitioned into two components, one that did not affect the average value of COP shift (“good variance”) and the other that did. An index (ΔV) was computed reflecting the relative amount of the “good variance”; this index has been interpreted as reflecting a multi-M-mode synergy stabilizing the COP trajectory. The average value of ΔV was similar across all sway frequencies; ΔV showed a within-a-cycle modulation at low but not at high sway frequencies. The modulation was mostly due to variations in the “good variance”. We conclude that muscle modes and their mapping on COP shifts are robust across a wide range of rates of COP shifts. Multi-M-mode synergies stabilize COP shifts (assure its reproducibility) within a wide range of its speeds, but only during cyclic COP changes. Taken together with earlier studies that showed weak or absent multi-M-mode synergies during fast discrete COP shifts, the results suggest a basic difference between the neural control assuring stability of steady-state processes (postural or oscillatory) and transient processes (such as discrete actions). Current results provide the most comprehensive support for the notion of multi-M-mode synergies stabilizing time profiles of important performance variables in motor tasks involving large muscle groups.