How providing more or less time to solve a cognitive task interferes with upright stance control; a posturographic analysis on healthy young adults

Contrasted postural effects have been reported in dual-task protocols associating balance control and cognitive task that could be explained by the nature and the relative difficulty of the cognitive task and the biomechanical significance of the force platform data. To better assess their respective role, eleven healthy young adults were required to stand upright quietly on a force platform while concomitantly solving mental-calculation or mental-navigation cognitive tasks. Various levels of difficulty were applied by adjusting the velocity rate at which the instructions were provided to the subject according to his/her maximal capacities measured beforehand. A condition without any concomitant cognitive task was added to constitute a baseline behavior. Two basic components, the horizontal center-of-gravity movements and the horizontal difference between center-of-gravity and center-of-pressures were computed from the complex center-of-pressure recorded movements. It was hypothesized that increasing the delay should infer less interaction between postural control and task solution. The results indicate that both mental-calculation and mental-navigation tasks induce reduced amplitudes for the center-of-pressure minus center-of-gravity movements, only along the mediolateral axis, whereas center-of-gravity movements were not affected, suggesting that different circuits are involved in the central nervous system to control these two movements. Moreover, increasing the delays task does not infer any effect for both movements. Since center-of-pressure minus center-of-gravity expresses the horizontal acceleration communicated to the center-of-gravity, one may assume that the control of the latter should be facilitated in dual-tasks conditions, inferring reduced center-of-gravity movements, which is not seen in our results. This lack of effect should be thus interpreted as a modification in the control of these center-of-gravity movements. Taken together, these results emphasized how undisturbed upright stance control can be impacted by mental tasks requiring attention, whatever their nature (calculation or navigation) and their relative difficulty. Depending on the provided instructions, i.e. focusing our attention on body movements or on the opposite diverting this attention toward other objectives, the evaluation of upright stance control capacities might be drastically altered.     

Load release balance test under unstable conditions effectively discriminates between physically active and sedentary young adults

This study investigates test-retest reliability and diagnostic accuracy of the load release balance test under four varied conditions. Young, early and late middle-aged physically active and sedentary subjects performed the test over 2 testing sessions spaced 1 week apart while standing on either (1) a stable or (2) an unstable surface with (3) eyes open (EO) and (4) eyes closed (EC), respectively. Results identified that test-retest reliability of parameters of the load release balance test was good to excellent, with high values of ICC (0.78–0.92) and low SEM (7.1%–10.7%). The peak and the time to peak posterior center of pressure (CoP) displacement were significantly lower in physically active as compared to sedentary young adults (21.6% and 21.0%) and early middle-aged adults (22.0% and 20.9%) while standing on a foam surface with EO, and in late middle-aged adults on both unstable (25.6% and 24.5%) and stable support surfaces with EO (20.4% and 20.0%). The area under the ROC curve >0.80 for these variables indicates good discriminatory accuracy. Thus, these variables of the load release balance test measured under unstable conditions have the ability to differentiate between groups of physically active and sedentary adults as early as from 19 years of age.     

Movement adjustments in preparation for single-leg jumps in individuals with functional ankle instability

There is some evidence showing that people with functional ankle instability (FAI) can present changes in postural control during the landing phase of a jump. These studies also show preliminary results indicating possible changes during phases prior to landing. Therefore, the objective of this study was to investigate whether movement adjustments prior to a jump are different between people with and without FAI. Sixty participants with (n = 30) and without (n = 30) FAI participated in this study. The main outcome measures were the variability of range of motion in ankle inversion/eversion and dorsiflexion/plantarflexion; and variability of center of pressure for the directions anterior-posterior and medio-lateral during the pre-jump period for drop jump, vertical jump and during single-leg stance. The group with instability showed more variability of center of pressure in anterior-posterior direction (p = 0.04) and variability of range of motion in ankle dorsiflexion/plantar flexion (p = 0.04) compared to control in the single-leg stance test. For the within-group comparisons, the group with instability showed more variability of center of pressure in anterior-posterior direction in the drop jump higher than single-leg stance and vertical jump. The same pattern was seen for the control group. Thus, this study suggests that people with FAI have greater ankle range of motion variability and center of pressure variability in the anterior-posterior axis when compared to healthy individuals during single-leg stance. For those same two variables, preparation for a drop jump causes more postural instability when compared to the preparation for a vertical jump and to single-leg stance.     

Are postural adjustments during reaching related to walking development in typically developing infants and infants at risk of cerebral palsy?

BackgroundIn typical development, postural adjustments during reaching change in the second half of infancy, including increasing rates of direction-specific adjustments. These changes are absent or different in infants at risk of cerebral palsy (CP). To discover whether these changes are related to acquisition of independent walking, we studied postural adjustments during reaching in infants before and after they learned to walk.MethodsTen typically developing (TD) infants and 11 infants at very high risk (VHR) of CP were assessed before and after they learned to walk. Reaching movements were elicited during supported sitting, while surface electromyography was recorded of arm, neck, and trunk muscles. Percentages of direction-specific adjustments (first level of control), and recruitment patterns and anticipatory activation (second level of control) were calculated.ResultsIn both groups, postural adjustments during reaching were similar before and after acquisition of independent walking. Direction-specificity increased with age in typically developing infants but not in VHR-infants.ConclusionIncreasing age rather than the transition to independent walking is associated with increasing direction-specificity of TD-infants during reaching while sitting, while infants at very high risk of CP show no increase in direction-specificity, suggesting that they gradually grow into a postural deficit.     

The use of implementation intentions and the decision balance sheet in promoting exercise behaviour

Although increasing exercise and fitness has often been associated with positive health outcomes, infrequent exercise participation has remained a problem. Since two distinct motivational and volitional phases to goal pursuit have been proposed, a combined motivational (decision balance sheet, DBS) and volitional (implementation intentions) intervention was predicted to be more effective in increasing exercise behaviour than a control or either strategy alone. A total of 86 students were randomly assigned to one of the four conditions, and were all asked to try to exercise two more times a week than they currently did, over a four week period. Their fitness levels were measured through fitness tests conducted pre- and post-intervention. A priori orthogonal contrasts indicated that the experimental strategies produced a greater increase in exercise frequency and total time spent exercising per week and accordingly showed greater fitness improvements than the control group. Moreover, the volitional groups taken together produced greater increase in time spent exercising and a marginally greater improvement in frequency than the DBS alone. The combined intervention led to improvements in fitness and marginal increases in frequency over the implementation intention alone group. It is proposed that for the combined group the DBS may have aided recall of the implementation intention or increased commitment to it, as remembering and then acting on the plan, in the stated place and time, mediated the implementation intention–behaviour relationship. The combined intervention produced the greatest fitness improvements, indicating that this strategy can lead to important health benefits.     

Distance and Movement Time Effects on the Timing of Agonist and Antagonist Muscles

The experiment examined the effects of movement time (MT) and distance on the timing of electromyographic (EMG) activity from an agonist and antagonist muscle during rapid, discrete elbow movements in the horizontal plane. According to impulse-timing theory (Wallace, 1981) MT, not distance moved, should have a pronounced effect on the timing of EMG activity (duration of initial agonist and antagonist burst and time to onset of initial antagonist burst). The levels of MT were 100 and 160 msec and the levels of distance were 27° and 45° of elbow flexion. In general support of impulse-timing theory, the results of the three EMG timing measures showed that MT had a more pronounced effect on these measures than distance. In addition, the timing of EMG activity in relation to total MT remained fairly consistent across the four MT-distance conditions.     

Postural Balance Following Aerobic Fatigue Tests: A Longitudinal Study Among Young Athletes

General fatigue can cause aggravation of postural balance, with increased risk for injuries. The present longitudinal study aimed to evaluate the postural balance of young athletes following field aerobic tests throughout 1 year of training. Thirty children from a sports center in Nazareth, participating in a 3 times/week training program (specific to basketball, soccer, or athletic training), were assessed. Postural balance parameters were taken before, immediately after, and 10 min after a 20 m shuttle-run aerobic test, at 3 time points during 1 training year (Start/Y, Mid/Y, and End/Y). Fitness improved at the Mid/Y and End/Y compared to Start/Y. Postural balance significantly deteriorated immediately after the aerobic test and improved significantly in the 10-min testing in all 3 time points, with significant deterioration in the End/Y compared with the Start/Y. In conclusions, postural balance deteriorates immediately after aerobic exercises, and at the end of the year. To better practice drills related to postural balance and possibly to prevent injuries, it is best for young athletes to properly rest immediately following aerobic exercises and to practice postural balance mainly at the beginning and at the middle of the training year.     

Sensory Integration and Response to Balance Perturbation in Overweight Physically Active Individuals

The purpose of this study was to compare sensory integration and response to balance perturbation between physically active normal weight and overweight adults. Physically active young adults were grouped into normal weight (n = 45) or overweight (n = 17) according to the World Health Organization body mass index classification for Asian adults. Participants underwent two balance tests: sensory organization and motor control. Overweight participants presented marginally lower somatosensory score compared to normal weight participants. However, they scored significantly higher in response to balance perturbation. There was no difference in the onset of participants' active response to balance perturbation. Physical activity might have contributed to improved muscle strength and improved the ability of overweight individuals to maintain balance.     

Hierarchical Error Evaluation: The Role of Medial-Frontal Cortex in Postural Control

Motor error evaluation appears to be a hierarchically organized process subserved by 2 distinct systems: a higher level system within medial-frontal cortex responsible for movement outcome evaluation (high-level error evaluation) and a lower level posterior system(s) responsible for the mediation of within-movement errors (low-level error evaluation). While a growing body of evidence suggests that a reinforcement learning system within medial-frontal cortex plays a crucial role in the evaluation of high-level errors made during discrete reaching movements and continuous motor tracking, the role of this system in postural control is currently unclear. Participants learned a postural control task via a feedback-driven trial-and-error shaping process. In line with previous findings, electroencephalographic recordings revealed that feedback about movement outcomes elicited a feedback error–related negativity: a component of the human event-related brain potential associated with high-level outcome evaluation within medial-frontal cortex. Thus, the data provide evidence that a high-level error-evaluation system within medial-frontal cortex plays a key role in learning to control our body posture.     

CONTAINING,TRANSLATING, AND INTERPRETIVE ACTING OUT

In analytic treatment, when patients project unspoken aspects of their internal self and object world, the analyst has to find ways to understand and communicate those expelled phantasies without the patient feeling accused, seduced, or persecuted; even when we do our best at interpreting such inner conflicts, the patient may experience our interpretations as assaults, forcing them to give up themselves or their hope for reconnecting with an object. The patient will resist or fight our efforts through the use of projective identification. Caught up in patient's projections, the analyst in turn may enact some of these phantasies by becoming the object rather than translating its presence in the transference, by overemphasizing one side over another of the patient's conflict, or by interpreting accurately but prematurely. These issues are illustrated in two case presentations and discussed in relation to the views of contemporary Kleinian writers on transference and countertransference.