Ron Croce

Comparison of isokinetic peak force and work parameters in youth with and without mental retardation

PURPOSEnThe purpose of this study was to compare isokinetic knee (flexion and extension) strength of nondisabled youth (ND; 15 males, 15 females; males = 12.7 +/- 2 yr; females = 13.4 +/- 2 yr) and youths with mental retardations (MR, 17 males + 13 females; male = 14.7 +/- 2 yr; females = 13.6 +/- 2 yr).nnnMETHODSnSubjects were evaluated on a Kin-Con isokinetic dynamometer at a speed of 60 degrees x s(-1). Parameters measured were peak torque (PT), time to PT, angle of PT, total work (W), and PT hamstrings/quadriceps (HQ) ratio. Peak torque was also corrected by weight (BW) and body mass index (BMI). Peak torque, time to peak torque, angle of peak torque, and total work were analyzed using a 2 x 2 x 2 (groups x gender x muscle) repeated measures analysis of variance (MANOVA). Flexion/extension ratios, BMI, and BW were analyzed by separate 2 x 2 (group x gender) analyses of variance.nnnRESULTSnResults of this study suggest that: 1) while gender differences are apparent in the ND population they are not evident in individuals with MR; 2) knee extension strength is higher for ND youth, thus causing lower PT HQ ratios when compared with those in youth with MR; 3) angle of PT and time to PT were similar among groups; and 4) total work performed is lower in individuals with MR.nnnCONCLUSIONSnIt was concluded that parameters of strength production in individuals with MR are not consistent and do not follow the same pattern as their nonretarded peers.

Effects of Time of Posttest after Two Durations of Exercise on Speed and Accuracy of Addition and Subtraction by Fit and Less-Fit Women:

18 adult female volunteers, ages 27 to 49 years, were divided into two groups based on their cardiorespiratory fitness to investigate speed and accuracy of addition and subtraction immediately, 5 min., and 15 min. postexercise. A 2 (fitness level) × 3 (exercise duration) × 3 (postexercise performance trials) repeated-measures analysis of variance indicated that, for the fit group, speed of problem solving was significantly faster after both 20-min. and 40-min. exercise sessions across all performance trials; for the less-fit group, speed of addition/subtraction was significantly faster only after the 20-min. exercise session across performance trials. No significant postexercise difference in accuracy was found for either fit or less-fit groups.

Variability of practice as an interface between motor and cognitive development

In this commentary, we highlight intriguing commonalities between the research areas of exercise and cognition and motor skill development and learning. While these two research domains have developed on separate tracks, the focus on variability of practice is central to both. We adopt a joint sport science and neuroscience approach to identify the characteristics of designed motor learning experiences that can impact brain plasticity and cognitive development. Novelty, diversity, effort, and successfulness seem essential ingredients to render learning experiences meaningful to this aim. All these characteristics belong to the construct of variability as it is conceived in the informational and ecological approaches to motor skill learning. To transition theory into practice, we discuss how variability of practice can impact cognitive and particularly executive function development. In this context, we address the role of flexibility training to support key transitions in the development of cognitive control, looking at the relation between repetition and change in physical activity in terms of trade-offs between costs and benefits of stability and flexibility. We conclude by reframing variability of practice into emerging models of embodied cognition, highlighting the potential of the proposed intersection of chronic exercise and cognition, cognitive development, and motor learning evidence to unwrap a new venue for sport sciences and quality physical education.

The influence of dual-task conditions on movement in young adults with and without Down syndrome

This investigation compared spatial and temporal movement parameters of a sample of young adults with Down syndrome (DS) (N=12) and individuals without disabilities (IWD) (N=12) under dual-task conditions. Subjects performed a walking task at a preferred speed in isolation and again while holding a plate and cup, carrying tray and cups, talking on a phone, or buttoning a shirt. Spatial and temporal values were compared using a 2 (group) × 5 (conditions) repeated measures analysis of variance. Analysis of spatial components separately indicated that step length, step width, stride length and stride width revealed significant group and condition interactions (p ≤.01). Temporal components yielded significance in velocity and single-leg support time (p ≤.01). The current results support the notion that along with impairments to qualitative motor skills, individuals with DS are also impaired in higher order executive functioning (EF), as measured by a dual-task paradigm. It was concluded that movements are less efficient and functional in individuals with DS when an additional task is encountered while walking. We theorized that the motor program was sufficient for general locomotion but was not sufficiently developed to allow individuals with DS to modify or alter their movements to changing cognitive conditions that increasingly taxed EF. As gait and balance are trainable in this population, we recommend developing appropriate exercise and motor skill interventions during childhood and adolescents to increase strength, stability, and more robust ambulatory motor schema.

Muscle Activation and Movement Responses in Youth with and without Mental Retardation

The reaction time ofindividuals with mental retardaI tion has been researched extensively in the past four decades. Consistently, researchers have shown that individuals with mental retardation have longer and more variable reaction times than those without mental retardation (see Anson & Mawston, 2000; Nettlebeck, 1980). Differences in reaction times have often been associated with central and peripheral processing components (Davis,Sparrow, & Ward, 1991; Inui,Yamanishi, & Tada, 1995; LeClair & Elliott, 1995; Un & Erbahceci, 2000) as well as structural alterations within the central nervous system (CNS; LeClair, Pollock, & Eiliot, 1993; Saccuzzo & Michael, 1984). While a plethora of research documents consistently longer and more variable reaction and movement times in individuals with mental retardation, the underlying mechanisms for these differences have not been extensively investigated. Davis (1987) suggested that muscle activation and electromyography (EMG) variability in responses could be the reason for the movement delays observed in this population. He further proposed that there is more trial-to-trial performance variability found in individuals with mental retardation. Although Davis (1987) suggested rationale for movement delays in individuals with mental retardation, to date no research has been conducted to confirm or refute these assertions. Therefore, the primary purpose of this study was to investigate differences in muscle activation and motor unit recruitment in boys with and without mental retardation

Spatial and Temporal Variability of Movement Parameters in Individuals with down Syndrome

This investigation compared spatial and temporal gait movement parameters of a sample of individuals with Down syndrome (n = 12) and one of individuals without disabilities (n = 12). All participants were evaluated on responses to a preferred pace and fast walk with the GAITRite Electronic Walkway. Spatial outcomes included step and stride length, step and stride width, toe-in/toe-out, and base of support. Temporal outcomes included step time, velocity, single and double leg support time, stance, and swing time. There were significant group differences for step length, step width, stride length, and velocity in the preferred walk condition. Significant group differences for step length, step width, and stride length were observed in the fast walk condition. Percentage differences also indicated lower scores for all spatial and temporal variables in relation to the control group. The ability to control gait movements appears to reflect earlier movement experiences, so it may be possible to use variable sensory feedback and specific training to modify and adjust movement responses and improve gait performance in Down syndrome.

Magnitude and Reliability of Measurements of Muscle Strength across Trials for Individuals with Mental Retardation

The purpose of this investigation was to examine the magnitude and reliability of strength measures on the Nicholas Manual Muscle Tester for individuals with mental retardation. 17 subjects were given six trials with the dominant and nondominant flexor and extensor muscle groups. No significant differences were found between dominant and nondominant muscle groups by side or by muscle group. Interclass correlations ranged from .96 to .98 for six and three trials, respectively. It was concluded that the test was appropriate for reliably assessing strength in this population and that these individuals can achieve a sufficient magnitude on three trials for a reliable measure of strength.

Information Processing and Motor Control in Down Syndrome

Extensive research on the motor performance of individuals with intellectual disabilities (ID) and more specifically individuals with Down syndrome (DS) reflects performance deficits in physical and motor functioning. Earlier study, indicated that low levels of physical function and deficiencies in sensory processing, memory consolidation, and postural control impact their ability to acquire and perform motor skills under variable environmental contexts. In addition, indicated that movements are often uncoordinated, slower, variable and hesitant in initiation, while other researchers reported longer movements and reaction times as well as difficulties in balance and postural control. Further limitations in spontaneous or symbolic play and limited opportunities to practice motor skills were observed in school and/or community settings, primarily during their developmental years. It is apparent that these individuals display delayed motor development and atypical motor functioning, which may be attributed to structural differences in the neurological system, delayed brain development, and a compromised somatosensory system.

Surface electromyographic alterations of the knee extensor musculature based on contraction intensity and velocity

The effect of contraction intensity (100%-, 75%-, 50%-, and 25%-maximum voluntary contraction (MVC)) and movement velocity (0 ◦ , 100 ◦ , 200 ◦ , 300 ◦ , and 400 ◦ /s) on the root mean square amplitude (SEMG-RMS) and median frequency power spectrum (SEMG-MPF) of the surface electromyography of the vastus medialis (VM) and rectus femoris (RF) muscles during isokinetic extension movements was investigated. Eight healthy female university students (age = 23.1 ± 2.6 yrs., mean height = 161.8 ± 6.8 cm, mean weight = 64.6 ± 6.1 kg) with no known knee pathologies participated in the study. Peak moment (PM), SEMG-MPF, and SEMG-RMS were analyzed using separate repeated measures analysis of variance (ANOVA). Results indicated (p 0.05): (1) an inverse relationship between PM and movement velocity, which was consistent with the literature and the force-velocity curve; (2) an increase in VM and RF SEMG-RMS across all isovelocity movements compared to isometric, with highest values occurring at 200 ◦ /s; (2) a linear increase in SEMG-RMS as force levels increased from 25%-MVC to100%-MVC; and, (3) an increase in SEMG-MPFvalues during isovelocity movements compared tothat found during isometric contractions, with highest values at 50 ◦ /s, suggesting isovelocity movements facilitated a greater recruitment of fast-twitchfibers. It appears that the degree to which the central nervous system activates muscle is based on the interplay of both contraction intensity and velocity needed to complete the required motor task.