Biomedical subjects

James S Frank

Publications and source records attributed to James S Frank.

10 recordsLinked to original sources

PubMed2006

Effects of postural anxiety on the soleus H-reflex.

Previous research has proposed that spinal reflex modulation may mediate anxiety-related changes in postural control. This study investigated how soleus H-reflex amplitude was influenced by standing at heights that induced different levels of anxiety. H-reflexes were elicited in 15 participants standing at the center and edge of a platform raised from a low to a high height (with and without vision). Increased skin conductance confirmed the anxiety effect of elevated surface heights. When standing at the edge of the platform with vision, H-reflex amplitude was attenuated in the high compared to low height condition. Changes in background muscle activity could not explain observed H-reflex changes, suggesting the potential involvement of pre-synaptic inhibition or fusimotor drive on anxiety-related changes in reflex modulation. This study reveals that healthy participants reduce spinal reflex excitability in the presence of increased postural anxiety and a postural threat imposed by standing at the edge of a raised platform. These findings have implications for understanding control of standing balance in individuals with postural instability and/or fear of falling, such as the elderly or stroke.

Adult↗

PubMed2006

Organization of postural responses following a rotational support surface perturbation, after TKA: sagittal plane rotations.

Proprioceptive dysfunction, related to osteoarthritis and total knee arthroplasty (TKA) may be related to changes in gait, and may result in balance impairment. This study examined the organization of postural responses to rotational support surface perturbations after TKA. Eight TKA patients and nine control participants volunteered. EMG was collected bilaterally from lower limb muscles. Kinematic data were collected using an OPTOTRAK system. The temporal pattern of muscle activation was preserved in both the surgical and sound limbs of the patient groups, while muscle activation amplitude was reduced. Knee joint angular displacement was reduced in both limbs among patients. COM displacement was not different. Patients demonstrated a different method in recovering posture control following a postural perturbation. Bilateral changes appear to reflect a simplification in the organization of the motor response, in response to the needs of the injured, or previously injured limb.

Aged↗

PubMed2006

Postural, physiological and psychological reactions to challenging balance: does age make a difference?

OBJECTIVES: To determine if increases in balance challenge influenced concomitant change in self-efficacy, state anxiety and physiological arousal, and if these changes were correlated with changes in standing balance in young and older adults. DESIGN: A 2 x 2 between- (age) by within-subject (balance challenge) factorial design. SETTING: quiet standing trials were performed on low and high support-surface heights in a research laboratory. SUBJECTS: 14 Young (22-31 years) and 14 older (60-83 years) adults with no known neurological or balance disorders, or falls within the last year. METHODS: Forceplate-derived measures of standing balance, measures of state anxiety, blood pressure and task-specific balance and coping self-efficacy. RESULTS: Independent of age, mean position, amplitude and frequency of centre of pressure displacements were significantly influenced by surface height, as were anxiety and efficacy. Decreased amplitude and increased frequency changes observed in both age groups with increased balance challenge were consistent with a stiffening strategy. Blood pressure, state anxiety and self-efficacy were correlated with different postural control changes in young and older adults. CONCLUSIONS: Older adults used the same stiffening strategy as young adults to cope with the increased anxiety and lowered confidence associated with standing on a high surface. Converging evidence indicates that physiological status, state anxiety and balance efficacy are related to specific changes in postural performance with increased balance challenge. Findings highlight the potential additive effects of psychological and physiological factors on clinical balance performance and the need to consider comprehensive rehabilitation and prevention techniques that concern psychological and physiological contributions to balance deficits.

Adult↗

PubMed2004

Locomotor adaptations for changes in the slope of the walking surface.

The goal of this study was to examine the transition of walking from a level surface onto different inclined surfaces. Kinematic data of limb and trunk segments were recorded from individuals as they approached and stepped onto four different ramped surfaces (slopes= 3 degrees , 6 degrees , 9 degrees , 12 degrees ). This transition introduced significant adaptations to the swing limb trajectory that were evident in even the lowest ramp condition and appear to be scaled to the ramp inclination although the nature of this scaling seemed to change between the 6 degrees and 9 degrees conditions. An increased forward pitch of the trunk orientation during all ramp conditions was initiated early on during the preceding stance phase on level ground. The swing limb modification essentially consisted of a two-stage response. The initial response of the limb trajectory changes was not specific to the degree of inclination but later changes were dependent on the ramp condition. The initial response is to ensure a safe toe clearance as the foot approaches the edge of the ramp and then later modifications provide the appropriate positioning of the limb to prepare for an elevated foot contact. Early changes were actively produced through an increased pull-off by the hip flexors and an elevation of the swing limb by the active muscle control of the stance limb. Ankle dorsiflexion also appears to have a supporting role increasing toe clearance. Absorption at the hip and knee during later swing contribute to control and position the limb in preparation for foot contact. These strategies were similar to those adopted for step changes in the level of the walking surface where there are similar demands of the quickly moving the limb forward and upward, however, the positioning of the limb for new angled landing surface requires further adaptations.

Adult↗

PubMed2004

Kinematic and kinetic validity of the inverted pendulum model in quiet standing.

Movements of the whole-body center of mass during quiet standing have been estimated from measurements of body segment movements. These whole-body center of mass movements have been compared with movements of the center of mass as predicted from a simple inverted-pendulum model of standing. However, the total body center of mass is a weighted average of the center of mass of all individual body segments. The question arises as to how well the total body center of mass represents the individual segments and lower limb joint angles. This study focuses on the validity of how well the individual segments and lower limb angles temporally and spatially synchronize with the total body center of mass. Eleven healthy university students volunteered to participate. Kinematic data were collected using a 3D optoelectronic camera system; kinetic data were collected using a 3D force plate. Participants stood quietly, with eyes open, for 120 s. Segment and whole body centers of mass were calculated from a 14 segment, 3D bilateral model. Segment and joint angles were calculated for the lower limbs, bilaterally, and the trunk. Segment center of mass root-mean-square displacements were strongly correlated with center of mass height relative to the ankle joint and were synchronized, or temporally locked, to the movement of the whole body center of mass. Sagittal plane ankle angular displacements were highly correlated to sagittal plane center of mass movement; stronger correlations between body center of mass and lower limb angular displacement were observed, the result of compensatory knee joint angular displacements. These data support and extend the use of an inverted pendulum model to represent quiet standing postural control.

Acceleration↗

PubMed2003

Fear of falling and postural control in Parkinson's disease.

This study investigated the relationship between fear of falling (FOF) and qualitative and quantitative postural control in Parkinson's disease (PD). Fifty-eight nondemented PD patients were studied along with age-matched healthy controls. The degree of FOF was estimated using the Activities-specific Balance Confidence scale. Qualitative postural control was evaluated using a component of the Unified Parkinson Disease Rating Scale. Postural control was quantified, using centre of pressure measures obtained from a force plate, for eight standing balance tests of different challenges. The results showed that FOF was more evident for PD patients when compared with healthy individuals of similar age. Furthermore, FOF was significantly associated with a qualitative estimate of postural control in PD; individuals with PD who had a greater degree of posture impairment reported greater FOF. The results also showed that an estimate of FOF may help to explain quantitative postural instability in PD. FOF, when coupled with a qualitative estimate of postural control, was able to explain a greater amount of variation in quantitative balance performance for five of the eight balance tests. When considered independently, the qualitative measure of postural control, in general, could not well predict quantitative balance performance. The greater degree of FOF and its possible association with altered postural control suggests that FOF should be considered as an important, independent risk factor in the assessment and treatment of postural instability in patients with PD.

Accidental Falls↗

PubMed2003

Balance and mobility challenges in older adults: implications for preserving community mobility.

Mobility is a critical component of most activities of daily living. Therefore, maintenance of mobility independence is essential for health and well-being. Balance control is a primary requirement for successful mobility. In this article, we first discuss the challenges to mobility and balance that older adults face within the community. Next, we examine the implications for preserving mobility, in particular the efficacy of different types of exercise-based interventions that have been used. Exercise and training done in relatively sterile environments, such as a laboratory, do not simulate the environmental challenges one faces in the community and are not particularly beneficial. In addition, the outcome measure(s) used to evaluate the success of the intervention programs need to reflect improvement in functional mobility within the community. We propose a mobility envelope measured from excursions into the community over a week as a likely candidate for outcome measure.

Accidental Falls↗

PubMed2003

Does articulation contribute to modifications of postural control during dual-task paradigms?

Many studies have been carried out to investigate the attentional resources required for postural control, using a 'dual-task' methodology in which performance on mental and postural control tasks is compared when these are carried out separately and concurrently. Most mental tasks used in these dual-task studies have employed verbal responses. However, changes in respiration during speech production are known to produce changes in postural control. Hence, the goal of this study was to determine whether articulation might contribute to the changes found in postural sway when a spoken mental task is being performed and to determine if the type of postural control measurement might also have an impact on the outcome of the study. Twenty young healthy participants were asked to stand on a force platform while executing secondary tasks that were performed silently or required a verbal response, and that required high or low levels of attention. Vision and postural task difficulty were manipulated. Performance of all tasks produced an increased sway frequency and decreased sway amplitude relative to the no task baseline. However, tasks that required articulation resulted in a more pronounced increase in postural sway frequency and sway path than did the tasks that did not require any articulation. These findings could imply that the addition of a secondary task results in increased stiffness, whereas articulation results in a further increased frequency of sway, which leads to an increase in sway path. We conclude that changes in the various parameters of sway that accompany performance of secondary tasks are complex, and are not always wholly attributable to attentional load, but may also be partly due to the motor requirements of the task, such as those involved in articulation.

Adult↗

PubMed2002

Fear of falling modifies anticipatory postural control.

This study investigated the influence of fear of falling or postural threat on the control of posture and movement during a voluntary rise to toes task for 12 healthy young adults. Postural threat was modified through alterations to the surface height at which individuals stood (low or high platform) and changes in step restriction (away from or at the edge of the platform) creating four levels of postural threat: LOW AWAY, LOW EDGE, HIGH AWAY and HIGH EDGE. To rise to the toes, an initial postural adjustment must destabilise the body so that it can be moved forward and elevated to a new position of support over the toes. Centre of pressure and centre of mass profiles, as well as tibialis anterior (TA), soleus (SO) and gastrocnemius (GA) muscle activity patterns were used to describe this behaviour. The results showed that the performance of the rise to toes task was significantly modified when positioned at the edge of the high platform. In this situation, the central nervous system reduced the magnitude and rate of the postural adjustments and subsequent voluntary movement. Although the duration of the movement was lengthened for this most threatening condition, the sequencing and relative timing of TA, SO and GA muscle activity was preserved. These changes in rise to toes behaviour were accompanied by evidence of increased physiological arousal and participant reports of decreased confidence, increased anxiety and decreased stability. Evidence of fear of falling effects on anticipatory postural control is clinically relevant as it may explain deficits in this control observed in individuals with balance disorders. For example, individuals with Parkinson's disease or cerebellar dysfunction demonstrate impaired performance on the rise to toes task as reflected in alterations of both the timing and magnitude of their anticipatory postural adjustments. Our findings suggest alterations in the magnitude of postural adjustments may be magnified by fear of falling while changes in the timing of postural adjustments may reflect underlying pathology.

Accidental Falls↗

PubMedDate not supplied

Does practice modify the relationship between postural control and the execution of a secondary task in young and older individuals?

BACKGROUND: Numerous daily activities require performing more than one task simultaneously, such as standing while engaging in a conversation. Recent studies have shown that postural control may be degraded when individuals are asked to perform a secondary task and that this effect seems to be more pronounced in older adults. Since various types of secondary tasks have been used in postural control studies, the novelty of the tasks may partly explain why dual-task interference occurs. It is known that novel tasks require greater attentional resources and thus may interfere to a greater extent with the performance of another task. Therefore, by practicing this dual-task situation, interference could perhaps be diminished. Since the dual-tasking efficiency is reduced with aging, practice could be very beneficial to older adults. OBJECTIVES: The main goal of this study was to examine whether practice could modify the changes seen in postural sway when individuals are asked to perform a secondary task while maintaining upright stance and whether older individuals could benefit to a greater extent from practice than would young individuals. The second goal was to examine the dual-task performance in young versus older adults and to determine whether older individuals benefit equally or to a greater extent from practice as compared with young individuals. METHODS: Young and older individuals were asked to stand on a force platform while performing a secondary task or no task. The secondary task condition was repeated six times to examine the effects of practice. RESULTS: Practice did not modify the performance of postural sway, but did lead to an increase in speed of execution of the secondary task for both groups equally. In young participants, the amplitude of sway was decreased, and the frequency of sway was increased, indicating an increased stiffness when performing the cognitive task. Older participants showed increased amplitude of sway and increased frequency of sway in the mediolateral direction only. CONCLUSIONS: Since the dual-task condition was only repeated six times, it could be hypothesized that the effect of practice would be greater, if more trials were added or if more practice sessions were included. More research is needed to verify this hypothesis.

Adult↗