Vicki Stemmons Mercer

Physical Activity as a Preventative Factor for Frailty: The Health, Aging, and Body Composition Study

BACKGROUND It is unclear if physical activity (PA) can prevent or reverse frailty. We examined different doses and types of PA and their association with the onset and severity of frailty. METHODS Health, Aging and Body Composition (Health ABC) study participants (N = 2,964) were followed for 5 years, with frailty defined as a gait speed of less than 0.60 m/s and/or inability to rise from a chair without using ones arms. Individuals with one impairment were considered moderately frail and those with both severely frail. We examined PA doses of volume and intensity, activity types (eg, lifestyle vs exercise activities), and their associations with incident frailty and transition to severe frailty in those who became frail. RESULTS Adjusted models indicated that sedentary individuals had significantly increased odds of developing frailty compared with the exercise active group (adjusted odds ratio [OR] = 1.45; 95% confidence interval [CI]: 1.04-2.01), whereas the lifestyle active did not. Number of diagnoses was the strongest predictor of incident frailty. In those who became frail during follow-up (n = 410), there was evidence that the sedentary (adjusted OR = 2.80; 95% CI: 0.98-8.02) and lifestyle active (adjusted OR = 2.81; 95% CI: 1.22-6.43) groups were more likely to have worsening frailty over time. CONCLUSIONS Despite the strong relationship seen between comorbid conditions and onset of frailty, this observational study suggests that participation in self-selected exercise activities is independently associated with delaying the onset and the progression of frailty. Regular exercise should be further examined as a potential factor in frailty prevention for older adults.

Detecting altered postural control after cerebral concussion in athletes with normal postural stability

Objective: To determine if approximate entropy (ApEn), a regularity statistic from non-linear dynamics, could detect changes in postural control during quiet standing in athletes with normal postural stability after cerebral concussion. Methods: The study was a retrospective, case series analysis of centre of pressure (COP) data collected during the Sensory Organization Test (SOT) from NCAA Division I (USA) athletes prior to and within 48 h after injury. Subjects were 21 male and six female athletes from a variety of sports who sustained a cerebral concussion between 1997 and 2003. After injury, athletes displayed normal postural stability equivalent to preseason levels. For comparison, COP data also were collected from 15 male and 15 female healthy non-athletes on two occasions. ApEn values were calculated for COP anterior-posterior (AP) and medial-lateral (ML) time series. Results: Compared to healthy subjects, COP oscillations among athletes generally became more regular (lower ApEn value) after injury despite the absence of postural instability. For AP time series, declines in ApEn values were much larger in SOT conditions 1 and 2 (approximately three times as large as the standard error of the mean) than for all other conditions. For ML time series, ApEn values declined after injury in all sensory conditions (F1,55 = 6.36, p = 0.02). Conclusions: Athletes who demonstrated normal postural stability after concussion nonetheless displayed subtle changes in postural control. Changes in ApEn may have represented a clinically abnormal finding. ApEn analysis of COP oscillations may be a valuable supplement to existing concussion assessment protocols for athletes.

Approximate entropy detects the effect of a secondary cognitive task on postural control in healthy young adults: a methodological report

BackgroundBiomechanical measures of postural stability, while generally useful in neuroscience and physical rehabilitation research, may be limited in their ability to detect more subtle influences of attention on postural control. Approximate entropy (ApEn), a regularity statistic from nonlinear dynamics, recently has demonstrated relatively good measurement precision and shown promise for detecting subtle change in postural control after cerebral concussion. Our purpose was to further explore the responsiveness of ApEn by using it to evaluate the immediate, short-term effect of secondary cognitive task performance on postural control in healthy, young adults.MethodsThirty healthy, young adults performed a modified version of the Sensory Organization Test featuring single (posture only) and dual (posture plus cognitive) task trials. ApEn values, root mean square (RMS) displacement, and equilibrium scores (ES) were calculated from anterior-posterior (AP) and medial-lateral (ML) center of pressure (COP) component time series. For each sensory condition, we compared the ability of the postural control parameters to detect an effect of cognitive task performance.ResultsCOP AP time series generally became more random (higher ApEn value) during dual task performance, resulting in a main effect of cognitive task (p = 0.004). In contrast, there was no significant effect of cognitive task for ApEn values of COP ML time series, RMS displacement (AP or ML) or ES.ConclusionDuring dual task performance, ApEn revealed a change in the randomness of COP oscillations that occurred in a variety of sensory conditions, independent of changes in the amplitude of COP oscillations. The finding expands current support for the potential of ApEn to detect subtle changes in postural control. Implications for future studies of attention in neuroscience and physical rehabilitation are discussed.

Characteristics of stepping over an obstacle in community dwelling older adults under dual-task conditions

Previous research suggests that older adults may have difficulty attending to simultaneous tasks. This study was conducted to determine how concurrent performance of a secondary cognitive task influences walking and stepping over an obstacle in community dwelling older adults. Twenty-one men and women with a mean age of 73.4 years (S.D.=5.3) participated in the study. Subjects performed a gait task both alone (single-task condition) and in combination with a cognitive task that involved reciting numbers (dual-task condition). In the gait task, each subject walked at his/her fastest speed along a 10-m walkway and stepped over an obstacle designed to simulate a door threshold. Paired t-tests were used to compare gait parameters (10 m gait speed, gait speed during obstacle approach and negotiation, medial-lateral center of pressure excursion and velocity during obstacle negotiation, foot clearance over the obstacle, step length and foot position relative to the obstacle) and cognitive task performance under single and dual-task conditions. Toe-obstacle distance was greater and obstacle-heel distance was reduced under dual-task conditions. Performance of the remaining gait parameters did not change with the addition of a secondary cognitive task. Cognitive task performance decreased under dual-task conditions. These community dwelling older adults demonstrated minimal or no change in measured gait parameters during simultaneous performance of a cognitive task. The observed decrement in cognitive task performance suggests that subjects may have placed a higher priority on gait performance.

Dual-task methodology: applications in studies of cognitive and motor performance in adults and children.

Purpose: The purpose of this article is to review the literature related to the application of dual‐task methodology in adults and children, particularly in the areas of gait and postural stability. Summary of Key Points: The interaction between cognitive factors and motor performance recently has received considerable attention in physical therapy research. Researchers often use dual‐task methodology to investigate the attentional demands of motor tasks or the effects of concurrent tasks on motor performance. The attentional demands of a task and the interference effects of concurrent tasks are influenced by a number of factors, including the performers age, level of skill, and the nature of the tasks involved. Even highly practiced activities, such as walking and postural control, are attention‐demanding, especially in individuals with impairments. Conclusions: An understanding of how attentional demands and other cognitive factors influence motor performance may be helpful to physical therapists in structuring intervention activities and in identifying children who have particular difficulty under dual‐task conditions. By modifying both cognitive and motor task demands, therapists can tailor their interventions to provide appropriate challenges for children at different skill levels.

Hip abductor and knee extensor muscle strength of children with and without down syndrome

Purpose: The purposes of this study were to 1) determine test‐retest reliability of hand‐held dynamometer measurements of right hip abductor and knee extensor muscle strength in children with Down syndrome (DS), 2) identify differences in isometric muscle strength between children with DS and peers who are developing typically, and 3) determine the relationship between various anthropometric and demographic variables and isometric muscle strength. Methods: Seventeen children with DS between the ages of seven and 15 years and a comparison group of 17 age‐ and gender‐matched peers who were developing typically participated in the study. A hand‐held dynamometer was used to measure peak force during maximal isometric right hip abduction and knee extension at two test sessions approximately one week apart. Peak torque values were calculated by multiplying peak force measurements by the appropriate segment lengths. Anthropometric measurements were obtained, and a questionnaire was used to measure habitual physical activity levels. Results: Test‐retest reliability was high, with intraclass correlation coefficients ranging from 0.89 to 0.95. Children with DS had significantly lower mean peak torque values for hip abduction and knee extension than children in the comparison group. Regression analyses indicated that weight, body mass index, height, activity level, and gender were significant predictors of peak torque production for the sample as a whole. Conclusions: Handheld dynamometry can be used to obtain reliable measurements of isometric muscle strength in children with DS. Anthropometric characteristics and activity levels may play a role in peak torque production in children with and without DS.

Are scores on balance screening tests associated with mobility in older adults

Purpose: To examine associations between measures of static and dynamic balance and performance of mobility tasks in older adults. Methods: A cross‐sectional analysis from 195 community dwelling participants (mean age 80.9 years, range 65 –103 years). Participants performed tests of static (tandem stance) and dynamic (360° turn) balance and mobility (walking speed and timed chair rise). Associations among balance and mobility measures were examined using correlation and logistic regression. Results: Static and dynamic balance were moderately associated (r = −.462). Relationships between dynamic balance and mobility were stronger than those between static balance and mobility. The association between dynamic balance and walking speed was particularly strong (r = −.701). Using logistic regression, age, and balance performance were significant predictors for outcomes of walking speed (dichotomized to < 1.0 m/s, ≥ 1.0 m/s), and timed chair rise (dichotomized to ≤ 13.6 s, > 13.6 s). Faster 360° turn times were independently associated with faster walking speed and chair rise time. Conclusion: Mobility tasks require both dynamic and static balance. As falls are a major health risk for older adults, including brief assessments of dynamic and static balance in the examination of older adults provides valuable information about physical function and mobility.

A Pilot Study: Coordination of Precision Grip in Children and Adolescents with High Functioning Autism

Purpose: This pilot study compared temporal coordination during a precision grip task between 13 children and adolescents with autism spectrum disorders (ASD) who were high functioning and 13 peers with typical development. Methods: Temporal coordination between grip and load forces was measured using latency between onset of grip and load forces, grip force at onset of load force, peak grip force (PGF), and time to PGF. Results: Compared with peers with typical development, participants with ASD demonstrated prolonged latency between grip and load forces, elevated grip force at onset of load force, and increased movement variability. PGF and time to PGF were not significantly different between the 2 groups. Conclusions: These findings indicate temporal dyscoordination in participants with ASD. The findings also enhance our understanding of motor coordination deficits in persons with ASD and have theoretical as well as clinical implications.

Infants Born Preterm Exhibit Different Patterns of Center-of-Pressure Movement Than Infants Born at Full Term

Background Infants born preterm are at risk for developmental impairments related to postural control. Objective The purpose of this study was to determine whether infants born preterm and infants born at full term differed in postural control at 1 to 3 weeks after term age. Design This study included 17 infants born preterm (mean gestational age=31.9 weeks, range=25.0–34.6) and 15 infants born at full term (mean gestational age=38.9 weeks, range=37.3–40.6). All infants were without diagnosed neurological or genetic conditions. Measurement Center-of-pressure (COP) data were recorded at 5 Hz while each infant was positioned supine on a pressure-sensitive mat in an alert behavioral state. Root mean square (RMS) displacement and approximate entropy (ApEn) were used to describe the COP movement variability in the time series. Differences between groups were identified using independent t tests. Results The COP time series were found to be deterministic, suggesting order in the time series. Infants born preterm exhibited significantly larger RMS values in the caudal-cephalic direction than infants born at full term (1.11 and 0.83 cm, respectively; t=−2.6, df=30, P=.01). However, infants born at full term had significantly larger ApEn values in the caudal-cephalic direction (1.19 and 1.11, respectively; t=2.4, df=30, P=.02). The 2 groups did not differ in RMS or ApEn values in the medial-lateral direction or the resultant. Conclusions Infants born at full term exhibited COP displacements in the caudal-cephalic direction that were smaller in amplitude, but may be considered more complex or less predictable, than those of infants born preterm. One explanation is that infants born preterm exhibited more stereotypic patterns of movement, resulting in large, but repetitive, COP excursions. A combination of linear and nonlinear measures may provide insight into the control of posture of young infants.

Effects of a dynamic versus a static prone stander on bone mineral density and behavior in four children with severe cerebral palsy.

Purpose: In this case series, we examined how two types of prone stander affected bone mineral density and behavioral variables in four children of preschool age with severe cerebral palsy. Methods: In phase one, four children of preschool age participated in an eight‐week standing program, standing for 30 minutes a day, five days a week. Two children stood in a conventional stander, and two stood in a new type of motorized (dynamic) stander that provides intermittent weight bearing. Measurements of bone mineral density before and after the program revealed increases in bone mineral density in both children who used a dynamic stander and one child who used a static stander. In phase two, all four subjects stood in both types of stander during three separate test sessions. Results: Measures of behavioral variables, including behavioral state, reactivity, goal directedness, and attention span, indicated little or no effect of type of stander on behavior. Conclusions: These results suggest there is potential value in additional research concerning the effects of static and dynamic standers on bone mineral density and behavior in children with cerebral palsy.