Biomedical subjects

V S Mercer

Publications and source records attributed to V S Mercer.

5 recordsLinked to original sources

PubMed2001

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: Hand-held 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.

Journal Article↗

PubMed2001

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 performer's 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.

Journal Article↗

PubMed2000

Effects of footwear on measurements of balance and gait in women between the ages of 65 and 93 years.

BACKGROUND AND PURPOSE: Footwear is not consistently standardized in the administration of the Functional Reach Test (FRT), Timed Up & Go Test (TUG), and 10-Meter Walk Test (TMW). This study was conducted to determine whether footwear affected performance on these tests in older women. SUBJECTS: Thirty-five women, aged 65 to 93 years, were recruited from assisted living facilities and retirement communities. METHODS: Each subject performed the FRT, TUG, and TMW wearing walking shoes, wearing dress shoes, and barefooted. Because of space constraints at the facilities where the testing was performed, 22 subjects performed the FRT and TUG on a linoleum floor and 13 subjects performed the tests on a firm, low-pile, carpeted floor. All 35 subjects completed the TMW on a firm, low-pile, carpeted floor. One-way repeated-measures analyses of variance (ANOVAs) and a Tukey Honestly Significant Difference test were used to compare the outcomes for the 3 footwear conditions, with separate ANOVAs conducted for the different floor surfaces for the FRT and TUG. RESULTS: Subjects performed better on the FRT when barefooted or wearing walking shoes compared with when they wore dress shoes, regardless of floor surface. Differences were found among all footwear conditions for the TUG performed on the linoleum floor and for the TMW. For these tests, the women moved fastest in walking shoes, slower barefooted, and slowest wearing dress shoes. CONCLUSION AND DISCUSSION: Footwear should be documented and should remain constant from one test occasion to another when the FRT, TUG, and TMW are used in the clinic and in research. Footwear intervention may improve performance of balance and gait tasks in older women.

Aged↗

PubMed1999

Postural synergies associated with a stepping task.

BACKGROUND AND PURPOSE: Synergistic relationships among multiple muscle components are thought to exist to simplify control of posture and movement. The purpose of this study was to examine the extent to which children, young adults, and older adults exhibit consistent sequences of postural muscle activation when lifting the right foot onto a step from a standing position. SUBJECTS: Twenty subjects without known impairments of the neuromuscular system (10 male, 10 female) in each of 3 age groups--children (8-12 years), young adults (25-35 years), and older adults (65-73 years)--participated. METHODS: A pressure switch taped to the subject's right foot was used to determine movement onset and offset. Latencies of muscle activation were determined using surface electromyography. A preferred postural synergy was defined as the sequence of postural muscle activation observed during the majority of trials for each subject. RESULTS: Mean movement times did not differ among age groups. Although the left tibialis anterior (TA) muscle was the first of the postural muscles activated in 93% of the trials, subjects displayed considerable variability in the subsequent order of postural muscle activation. Across subjects, a total of 14 different preferred postural synergies were observed. Age groups did not differ in the number of different synergies. CONCLUSION AND DISCUSSION: Early TA activation may reflect biomechanical constraints of the stepping task, producing forward displacement of the center of mass over the changing base of support. The fact that subjects of all ages were quite variable in the specific sequences of muscles activated subsequent to the TA suggests that, for this type of task, therapists should not focus their interventions on facilitating execution of particular synergy patterns.

Adolescent↗

PubMed1997

Age Group Differences in Postural Adjustments Associated With a Stepping Task.

In this study, differences among age groups in the postural adjustments associated with a stepping task were identified. Twenty subjects from each of 3 age groups, children (8-12 years), young adults (25-35 years), and older adults (65-73 years), performed the task in 2 movement contexts: place and step. In place, the subject simply lifted the foot and placed it on the step. In step, the subject lifted the foot, placed it on the step, and stepped up onto the step. Latencies of postural and focal muscle activation were determined by using surface electromyography and pressure switches. Center of pressure (CP) data were obtained by using a force platform. Subjects in all 3 age groups consistently demonstrated postural adjustments before movement initiation. Children displayed longer postural latencies than young adults as well as disproportionately large values for CP path length. Older adults showed prolonged postural-focal latencies and decreased CP excursions compared with the 2 younger age groups. These results suggest that maturation of coordination between posture and movement may not be fully complete in 8- to 12-year-olds and that increased restraint characterizes the performance of postural adjustments in healthy persons over 65 years of age.

center of pressure↗