bluuebunny/crossref_metadata_2025 huggingface dataset:
Pointing to an Allocentric and Egocentric Remembered Target
Authors: Lemay Martin , Bertram Christopher P. , Stelmach George E.
Published: August 2016

Pointing to a visual target that disappears prior to movement requires the maintenance of a memory representation about the location of the target. It has been shown that a target can be stored egocentrically, allocentrically, or in both frames of reference simultaneously. The main goal of the present study was to compare the accuracy and kinematics of a pointing movement to a remembered target when egocentric, allocentric, or combined egocentric and allocentric coding was possible. The task was to localize, memorize, and reach to a remembered target. Condition 1 was the “no-context” condition and involved presenting the target in a completely dark environment (egocentric condition). For 2 other conditions, the target was presented within a visual context provided by an illuminated square. Condition 2 was the “stationary-context” condition and involved keeping the context at the same position during the whole trial (egocentric and/or allocentric coding). Condition 3 was a “moved-context” condition that involved shifting the context to a different location during the recall delay (allocentric coding). Movement accuracy and kinematics results were strikingly similar for the moved-context and stationary-context conditions. These results suggest that when both allocentric and egocentric coding are possible, an allocentric strategy is used.
Roles of Motor-Unit Recruitment in Producing Force Variability of Simulated Muscle Contractions
Authors: Yao Wan X.
Published: August 2016

The purpose of this study was to examine the effect of motor-unit recruitment on force variability by using computer simulated isometric contractions of a hand muscle (i.e., first dorsal interosseus). The force was simulated at 10 levels of excitation, ranging from 10 to 100% of maximum. Two recruitment conditions were simulated to compare the relative effect of motor-unit recruitment (MUR) on the relationship of force variability and level of force. One condition (40%MUR) recruited all motor units at 40% of the maximum excitation level, and the other (50%MUR) recruited all motor units at 50% of the maximum. The 40%MUR condition had a greater number of motor units than the 50%MUR group before the excitation level reached 50% of the maximum. The results showed that force variability increased at a faster rate before the completion of motor-unit recruitment and, thereafter, increased at a slower rate. In addition, the 40%MUR group showed greater force variability than the 50%MUR group. These data suggest that motor-unit recruitment is an important factor in causing force variability.
Task-specific Stabilization of Postural Coordination during Stance on a Beam
Authors: Oullier Olivier , Bardy Benoît G. , Stoffregen Thomas A. , Bootsma Reinoud J.
Published: August 2016

Surfaces shorter in extent than the feet elicit multi-joint coordination that differs from what is elicited by stance on extensive surfaces. This well-known effect arises from the mechanics of the actor-environment interaction. Multi-joint control of stance is also known to be influenced by non-mechanical aspects of a situation, including participants' task or intention. Intentional constraints do not originate in mechanics, and for this reason one might suppose that constraints imposed by mechanics would dominate constraints imposed by intentions, when the two were in conflict. We evaluated this hypothesis by varying participants' supra-postural task during stance on a short surface. While standing on a 10-cm wide beam, participants were exposed to optic flow generated by fore-aft oscillations of a moving room. Participants faced a target attached to the front wall of the moving room and were asked either to look at the target (with no instruction to move) or intentionally to track it with their head (i.e., to keep the target-head distance constant). Within trials, we varied the frequency of room (and target) motion, from 0.15 to 0.75 Hz, in steps of 0.05 Hz. In both conditions, ankle and hip rotations exhibited antiphase coordination, but behavior was not identical across conditions. Coupling between motion of the room and the head was stronger for the tracking task than for the looking task, and the stability of ankle-hip coordination was greater during tracking than during looking. These results indicate that the influence of support surface mechanics did not eliminate the influence of the supra-postural task. Environment-based and task-based constraints interacted in determining the coordination of hips and ankles during stance.
Rotational Equilibrium during Multi-Digit Pressing and Prehension
Authors: Latash Mark L. , Shim Jae Kun , Gao Fan , Zatsiorsky Vladimir M.
Published: August 2016

We review a series of studies that show stabilization of the moment of a couple produced by a set of digits in many maximal and submaximal accurate force production tasks that have no requirements for the moment. In particular, an unusual and novel multi-digit force production task shows stabilization of the total moment while the total force requires extensive practice to be stabilized. Similar results were obtained in persons with Down syndrome during easier tasks. During prehension, changes in digit forces and coordinates of their points of application suggest the presence of two multi-digit synergies whose purpose is to assure a certain grip force and a certain total moment, respectively. Elderly persons show impaired production of both maximal and submaximal moments that goes beyond their documented loss of muscle force. We conclude that moment production (keeping rotational equilibrium) is a central constraint in a variety of multi-digit tasks that has received little attention. Analysis of digit interaction for moment production during handwriting could signify a major step towards understanding the control of this action.
Age-Related Differences in the Control of Multijoint Movements
Authors: Ketcham Caroline J. , Dounskaia Natalia V. , Stelmach George E.
Published: August 2016

The present study investigates whether regulation of interactive torque during multijoint movements decays with advanced age as a result of declines in the motor system. Young and elderly adults repeatedly drew a circle and ovals oriented in different directions using shoulder and elbow joint movements. Each template was traced at three levels of cycling frequency with and without vision. Although vision did not affect performance, increases in cycling frequency caused distortions of movement trajectories in both groups. The pattern of distortions differed, however, between the groups. These differences were accounted for by differences in elbow control. Young adults provided regulation of elbow amplitude and timing by matching muscle torque magnitude with increased interactive torque. In contrast, elderly adults did not increase muscle torque magnitude and modulated torque timing for elbow motion regulation. This strategy is discussed as adaptation to decrements in the aging motor system.
Are Graphomotor Tasks Affected by Working in the Contralateral Hemispace in 6- to 10-Year-Old Children?
Authors: Smits-Engelsman Bouwien C. M. , Swinnen Stephan P. , Duysens Jacques
Published: August 2016

It has been shown that crossing the midline affects the performance of fine motor skills but the underlying mechanisms are not well understood. This issue is particularly important with respect to the development of motor activities such as writing or pointing in children. Forty-eight right-handed children performed goal-directed movements toward targets positioned either at the midline, or in the left (contralateral side), or right (ipsilateral) hemispace. Findings revealed that movements were more accurate in ipsilateral than in contralateral space and their overall accuracy increased by 42% between 6 and 10 years of age. Differences in movement time among hemispaces depended on the joints predominantly involved in producing the movements (wrist versus fingers). Lower accuracy of movements in contralateral workspace is also present when participants do not have to cross the midline but only move within this workspace. In motor proficient children, no developmental trends were found for these hemispace effects.
Learning Multiple Visuomotor Transformations: Adaptation and Context-Dependent Recall
Authors: Mistry Sima , Contreras-Vidal Jose L.
Published: August 2016

Recent motor control theories suggest that the brain uses internal models to plan and control accurate movements. An internal model is thought to represent how the biomechanics of the arm interacting with the outside world would respond to a motor command; therefore it can be seen as a predictive model of the reafference that helps the system plan ahead. Moreover, adaptation studies show that humans can learn multiple internal models. It is not clear, however, whether and how contextual cues are used to switch among competing internal models, which are required to compensate for altered environments. To investigate this question, we asked healthy participants to perform center-out pointing movements under normal and distorted visual feedback (0°, 30° counterclockwise, and 60° clockwise rotation of hand-screen cursor relationships) conditions. The results suggest that humans can learn multiple environments simultaneously and can use contextual cues to facilitate adaptation and to recall the appropriate internal model of the visuomotor transformation.
Speed–Accuracy Trade-Off in Voluntary Postural Movements
Authors: Duarte Marcos , Freitas Sandra M.S.F.
Published: August 2016

We investigated the speed and accuracy of fast voluntary movements performed by the whole body during standing. Adults stood on a force plate and performed rhythmic postural movements generating fore and back displacements of the center of pressure (shown as online visual feedback). We observed that for the same target distance, movement time increased with the ratio between target distance and target width, as predicted by Fitts’–type relationships. For different target distances, however, the linear regressions had different slopes. Instead, a single linear relation was observed for the effective target width versus mean movement speed. We discuss this finding as a result of the pronounced inherent variability of the postural control system and when such a source of variability is considered, the observed relationship can be explained. The results reveal that the accuracy of fast voluntary postural movements is deteriorated by the variability due to sway during standing.
Adaptation to Separate Kinematic and Dynamic Transformations in Children and Adults
Authors: Jansen-Osmann Petra , Richter Stefanie , Schinauer Thomas , Fuchs Petra , Kalveram Karl-Theodor
Published: August 2016

The question addressed in the present study is whether children and adults are able to combine and decompose separate kinematic (visual-feedback-shift) and dynamic (velocity-dependent force) transformations in goal-directed arm movements. A total of 64 participants (32 adults and 32 children) performed horizontal forearm movements using a single-joint arm manipulandum. When participants first learned kinematic and dynamic transformations separately, target error decreased in a subsequent combined transformation task. This effect was based on previous learning of the kinematic transformation. When they first learned the combined transformation, target error was smaller in the following kinematic—but not in the dynamic—transformation. No difference was found in adaptation performance between children and adults. The results suggest that there are two separate models for the kinematic and dynamic transformation and that a possible differentiation of kinematic and dynamic features of the motor task might already be present at age 11.
Role of Limb and Target Vision in the Online Control of Memory-Guided Reaches
Authors: Heath Matthew
Published: August 2016

This investigation tested the proposal that a “highly accurate” and temporally unstable stored target representation is available to the motor system for the online control of memory-guided reaches. Participants reached to a target that was: (a) visible during the response, (b) extinguished at movement onset, and (c) occluded for 0, 500, 1500 and 2,500 ms in advance of response cueing. Additionally, trials were performed with (i.e., limb visible) and without (i.e., limb occluded) vision of the reaching limb. Results showed that limb occluded trials undershot the target location in each target condition, and were characterized by a primarily offline mode of control. In contrast, limb visible trials showed a consistent level of endpoint accuracy for each target condition and elicited more online reaching corrections than limb occluded trials. It is therefore proposed that a reasonably accurate and temporally stable stored target representation can be combined with vision of the moving limb for the online control of memory-guided reaches.
Probing Expert Anticipation with the Temporal Occlusion Paradigm: Experimental Investigations of Some Methodological Issues
Authors: Farrow Damian , Abernethy Bruce , Jackson Robin C.
Published: August 2016

Two experiments were conducted to examine whether the conclusions drawn regarding the timing of anticipatory information pick-up from temporal occlusion studies are influenced by whether (a) the viewing period is of variable or fixed duration and (b) the task is a laboratory-based one with simple responses or a natural one requiring a coupled, interceptive movement response. Skilled and novice tennis players either made pencil-and-paper predictions of service direction (Experiment 1) or attempted to hit return strokes (Experiment 2) to tennis serves while their vision was temporally occluded in either a traditional progressive mode (where more information was revealed in each subsequent occlusion condition) or a moving window mode (where the visual display was only available for a fixed duration with this window shifted to different phases of the service action). Conclusions regarding the timing of information pick-up were generally consistent across display mode and across task setting lending support to the veracity and generalisability of findings regarding perceptual expertise in existing laboratory-based progressive temporal occlusion studies.
Movement-Accuracy Control in Tetraparetic Cerebral Palsy: Effects of Removing Visual Information of the Moving Limb
Authors: van Roon Dominique , Steenbergen Bert , Meulenbroek Ruud G.J.
Published: August 2016

People with cerebral palsy (CP) are known to rely heavily on visual guidance when making targeted upper-limb movements. In the present study, we examined whether being able to visually monitor the moving limb forms a precondition for people with CP to make accurate upper-limb movements. Eight participants with tetraparetic CP and eight controls were asked to produce large-amplitude, straight-line drawing movements on a digitizing tablet. In half the trials, vision of the moving limb was blocked. Accuracy constraints were manipulated by varying the width of the target and by imposing a maximum width of the movement path. Surprisingly, when vision was blocked movement accuracy was comparable in the two groups. Thus, people with tetraparetic CP do not strictly require constant vision of their moving limb to make accurate upper-limb movements. They compensated for the lack of visual information, however, by prolonging movement time. Using a high pen force proved a general strategic adaptation, possibly to filter out unwanted noise from the motor system or to enhance proprioceptive input.
Ground Reaction Forces in Children’s Gait
Authors: Greer Nancy L. , Hamill Joseph , Campbell Kevin R.
Published: August 2016

Ground reaction force patterns during walking were observed in 18 children 3 and 4 years of age. The children walked barefoot at a self-chosen walking pace. Selected variables representing the vertical, anteroposterior, and mediolateral force components were evaluated. The results indicated that children in this age range contact the ground with greater vertical force measures relative to body mass than do adults. In addition, the minimum vertical force was lower, the transition from braking to propulsion occurred earlier, and the mediolateral force excursions were higher than typically found in adults. When the children were divided into groups on the basis of sex, differences were observed between those groups. The boys exhibited a greater difference in the vertical peak forces, a lower minimum force, a greater braking force, and a higher mediolateral force excursion value. The results indicated that children display a different ground reaction force pattern than do adults and that differences between boys and girls may be observed as early as ages 3 and 4 years.
Physiological Effects of a Physical Training Program in Children with Exercise-Induced Asthma
Authors: King M. Jonathan , Noakes Timothy David , Weinberg Eugene Godfrey
Published: August 2016

Twelve boys with atopic asthma, ages 9-14 years, were divided equally into exercise and control groups. Identical measurements were made before and after a 3-month trial period during which the exercise group was trained. The trained group, but not the control group, showed significant improvements in parameters of physical fitness including maximum oxygen consumption (V̇O2max) and peak running velocity during the maximal treadmill test (p<0.05). Treadmill velocity at the lactate tumpoint was greater and heart rate during submaximal exercise was lower in the trained subjects after the trial period. Subjective and objective findings (less use of medication, fewer asthmatic attacks, increased physical activity) suggested that clinical asthma improved with training. However exercise-induced asthma (EIA), measured by the airway’s response to a standardized treadmill run, did not alter with training.
The Effects of Upper Body Resistance Training on Prepubescent Children
Authors: Siegel Judith A. , Camaione David N. , Manfredi Thomas G.
Published: August 2016

To assess the effects of a group resistance exercise program on prepubescent children, an experimental group of boys (n = 26) and girls (n = 24), with a mean age of 8.4 ± 0.5 years, participated in 12 weeks of school based training. The program consisted of upper body exercise using hand-held weights, stretch tubing, balls, and self-supported movements. A control group of boys (n = 30) and girls (n = 16), mean age 8.6 ± 0.5 years, had a free-play period. Boys were significantly stronger than girls on all initial strength evaluations and were taller and had lesser skinfold sums. ANCOVA was used to evaluate pre/post changes in cable tensiometer elbow flexion and extension, right and left handgrip strength, pull-ups, flexed arm hang, sit-ups, sit-and-reach flexibility, and body composition parameters. Following the training period, significantly greater gains were made by the experimental group for right handgrip, flexed arm hang, pull-ups, and flexibility. Greater decreases in sum of skinfolds were also found. Training responses of boys and girls were similar. It was concluded that a group strength training program can be an effective means of increasing fitness levels and improving body composition in both boys and girls of this age.
Muscular Efficiency during Treadmill Walking: The Effects of Age and Workload
Authors: Kanaley Jill A. , Boileau Richard A. , Massey Benjamin H. , Misner James E.
Published: August 2016

Changes in muscular efficiency as it relates to age were examined during inclined submaximal treadmill walking in 298 boys ages 7–15 years. Furthermore, the changes in efficiency with increased work intensity (67–90% V̇O2max) were studied. Efficiency was expressed as submaximal oxygen consumption (V̇O2) and was calculated mathematically as energy out/energy in = (vertical distance) (wt of subject)/(V̇O2 L • min−1) (kcal equivalent). Efficiency, calculated mathematically, was found to significantly increase (p<.01) with age, with the younger children (<9 yrs) being less efficient than the older children (13–15 yrs). These values ranged from 12.8% for the youngest boys (<9 yrs) to 16.4% for the oldest boys (13–15 yrs). In addition, efficiency significantly increased in a linear fashion (p<.01) during submaximal workloads within each age group. No significant interactions (p>.05) between age and workload were found. These values are lower than gross efficiency values during cycling previously reported in the literature for adults; however, they support earlier findings that children increase in efficiency with age and work intensity, regardless if expressed as efficiency or V̇O2 (ml • kg−1 •min−1). These findings suggest that parameters associated with growth and development may influence muscular efficiency with age.
Children’s Motivation for Participation in and Withdrawal from Sport: Identifying the Missing Links
Authors: Weiss Maureen R. , Petlichkoff Linda M.
Published: August 2016

Children’s reasons for participating in sport as well as their reasons for discontinuing involvement have been extensively studied over the last decade. However, a complete understanding of the underlying processes influencing these phenomena has been clouded by failing to consider a number of individual difference and contextual factors related to sport participation. These missing links include participant status group differences, program type, level of intensity, type of sport, particular reasons for attrition, multiple assessments across a season, developmental differences, and the social structure surrounding the sport experience. Future research possibilities and practical implications for pediatric educators are provided.
Anaerobic Threshold in Children
Authors: Washington Reginald L.
Published: August 2016

The ventilatory anaerobic threshold (VAT) occurs when there is an isolated increase in the slope for ventilator equivalent for oxygen consumption (VE/VO2) with no change in the slope for ventilatoiy equivalent for carbon dioxide production (VE/VCO2) when both are plotted against time. The concept of anaerobic threshold remains controversial. However, it is a clinically useful tool in evaluating the exercise capacity of children. This paper will review the history, biochemistry, and methodology involved in determining the anaerobic threshold, as well as the ventilatory anaerobic threshold in children.
Fractional Utilization of Maximal Aerobic Capacity in Children 6 to 8 Years of Age
Authors: Krahenbuhl Gary S. , Pangrazi Robert P. , Stone William J. , Morgan Don W. , Williams Tracy
Published: August 2016

Untrained 6- to 8-year-old children (N = 80) served as subjects in a cross sectional study of the fractional utilization of maximal aerobic power during submaximal running. Using the open-circuit method, the absolute oxygen demands of submaximal running were found to increase with age. When expressed relative to body weight, oxygen demands of submaximal running showed no statistically significant changes over the 3-year span. VO2max increased 36.2%, which was proportionally greater than the percentage increase for either body weight (28.4%) or the absolute oxygen demands of submaximal running (22.9%). Thus, during the span of years studied there was a significant reduction in the fractional utilization of maximal aerobic power required to run at a fixed submaximal speed.
The Relationship between Perceived Exertion and Heart Rate in Children and Adults
Authors: Gillach Mary C. , Sallis James F. , Buono Michael J. , Patterson Patricia , Nader Philip R.
Published: August 2016

This study examined the relationship between heart rate (HR) as a measure of physiological strain and ratings of perceived exertion (RPE) in 193 children (mean age = 11 yrs) and 188 adults (mean age = 36 yrs) during submaximal cycle ergometry. Two methods of correlating HR and RPE were compared. Computing correlations (r) for each individual’s data and then taking the group mean produced very high rs, ranging from 0.92 to 0.95. Correlating HR and RPE for the entire group at all powers simultaneously produced much lower rs, ranging from 0.63 to 0.65. Correlations were essentially the same for children and adults, and there was no evidence of a practice effect. The results indicated that (a) children in this age group were as capable of expressing RPE as adults, and (b) absolute levels of perceived exertion were not predictive of physiological strain (as indicated by heart rate).
Longitudinal Assessment of Aerobic Fitness in Middle School African-American Girls
Authors: Pivarnik James M. , Taylor Wendell C. , Cummings Sharon S.
Published: August 2016

This study presents 3 years of data from a longitudinal study designed to follow changes in VO2max and treadmill (TM) exercise performance in African-American girls throughout middle school. Subjects (N = 19) were tested 6 months apart during grades 6-8. VO9 and heart rates (HR) were measured continuously while each subject performed an incremental TM test to volitional exhaustion. Absolute VO2max (ml • min1) increased with time, while relative (ml • kg 1 * min1) values declined significantly from 6th to 8th grade. Treadmill time to exhaustion improved after the first test, but showed a significant decline by the end of 8th grade. Correlations between fall 6th-grade and spring 8th-grade aerobic fitness measures ranged from .35 to .57, indicating moderate tracking of these variables throughout middle school. Aerobic fitness values are low (compared to Caucasians) in African-American adolescent girls and show significant declines throughout middle school. Future studies should investigate anatomical, physiological, and behavioral reasons for the apparently low aerobic fitness seen in African-American girls.
Bone Mineral Density in Weight-Bearing and Nonweight-Bearing Female Athletes
Authors: Rourke Kathleen M. , Bowering Jean , Turkki Pirkko , Buckenmeyer Philip J. , Thomas F. Deavor , Keller Betsy A. , Sforzo Gary A.
Published: August 2016

Bone mineral density (BMD) development and maintenance is enhanced with weight-bearing exercise, while bed rest and zero gravity results in BMD loss. The purpose of this study is to determine if BMD is significantly different in female athletes engaged in weight-bearing versus nonweight-bearing sports. Six BMD sites and anthropometric measurements were assessed at 3 equal intervals utilizing 2-way ANOVA’s. Controlling for body-weight, differences in BMD were investigated utilizing ANCOVA. Pearson and Spearman Rank Correlations were utilized to investigate interrelationships between anthropometric, VO2max, and BMD measurements. Swimmers were taller and heavier with greater percent, body fat. BMD was significantly different between runners and swimmers only at the distal, which was higher for swimmers at 6 months. There was no difference in radial BMD when utilizing ANCOVA, with weight serving as the covariate. Swimming does not appear to be a contraindicated activity for BMD accrual and maintenance.
Relationships among Muscle Endurance, Explosiveness, and Strength in Circum-Pubertal Boys
Authors: Suei Kensaku , McGillis Leslie , Calvert Randy , Bar-Or Oded
Published: August 2016

We assess relationships among muscle endurance, strength, and explosiveness in forty-eight 9.6- to 17.0-year-old males divided into 3 maturational groups (Tanner Stages I, II-IV, and V). Peak torque during isometric knee extension and flexion was averaged to reflect strength. Mechanical power in the Sargent vertical jump was taken as explosiveness, and total work in the Wingate test reflected muscle endurance. Correlations (3 groups combined) among the variables, expressed in absolute terms, were r = .82 to .92, but only -.11 to .70 when expressed per body mass or lean thigh size. These correlations were distinctly lower in the Tanner V boys than in the 2 less-mature groups, which may suggest that specialization into discrete muscle performance characteristics does not occur before late puberty.
Increasing Physical Activity of Children with Cystic Fibrosis: A Home-Based Family Intervention
Authors: Tuzin Beverly J. , Mulvihill Mary M. , Kilbourn Kristin M. , Bertran Deborah A. , Buono Michael , Hovell Melbourne F. , Harwood Ivan R. , Light Michael J.
Published: August 2016

This study evaluated a home-based, parent-managed, behavioral program to increase routine physical activity of ten 7-to 14-year-old children with cystic fibrosis. In each of 3 replications of a multiple baseline design, physical activity increased only after the intervention was initiated. Eight children increased total activity 42.5% to 321 %, and 2 children exercised more consistently. Study II recorded further activity increases at 6-week follow-up. Study III validated reported activity with increases of 7% to 27% in VO2max, 8% and 31.6% in VEmax, and 14.2% and 20% in Wmax. Results suggest that a home-based contingency management program can increase physical activity among chronically ill children with cystic fibrosis. Future studies are needed to assess maintenance and possible health benefits.
Application of the Transtheoretical Model of Behavior Change to Preadolescents’ Physical Activity and Exercise Behavior
Authors: Cardinal Bradley J. , Engels Hermann-J. , Zhu Weimo
Published: August 2016

The Transtheoreticai Model of behavior change was applied to a sample of 669 preadolescents (M age = 8.2) to determine whether stages of exercise could be observed. Associations between stage of exercise classification and demographic, fitness, and cognitive variables were examined. Stage of exercise classifications, on the basis of the Children’s Stage of Exercise Algorithm, were as follows: maintenance (50.8%), action (36.5%), preparation (3.1%), contemplation (4.9%), and precontemplation (4.6%). Stage of exercise was significantly related to gender, age, and grade level. Controlling for these differences, the relationship between exercise beliefs and stage of exercise was significant.
Russian and British Children’s Physical Self-Perceptions and Physical Activity Participation
Authors: Hagger Martin , Ashford Basil , Stambulova Natalia
Published: August 2016

This study examined cross-cultural differences between Russian and British children’s physical self-perceptions and physical activity levels. The relationship between physical self-perceptions and physical activity behavior was also investigated. Two hundred and fifty-two Russian children (118 boys, 134 girls) and 240 British children (113 boys, 127 girls) aged 13 to 14 years completed Whitehead and Corbin’s (32) Physical Self-Perception Profile for Children (PSPP-C) and the leisure time exercise questionnaire (11). Results showed that boys from both nationalities were significantly more active than their female counterparts, and Russian boys participated in more moderate intensity activity than British girls. Multisample confirmatory factor analyses revealed that Russian and British children appraised the PSPP-C subdomains in similar ways, but the fit of the data to the hypothesized model was unsatisfactory. Russian children exhibited gender differences on all of the PSPP-C subdomains, but there was only one gender difference for the body-attractiveness subdomain in British children.
Physical Activity of 6-Year-Old Children: Validation of Two Proxy Reports
Authors: Manios Yannis , Kafatos Anthony , Markakis George
Published: August 2016

Heart rate monitoring was used to evaluate the validity and reliability of 2 proxy report measures in assessing moderate to vigorous physical activity (MYPA) in 39 six-year-old children. Significant positive correlations were found between the proxy measures and corresponding heart rate data for school hours and leisure time, respectively (teacher reports, r = .58, p < .001; parent reports, r = .71 to .81, p < .001), but these decreased when each proxy measure was compared with heart rate data collated over a 3-day period (teacher reports, r = .40, p = .01; parent reports, r = .68, p < .001). Repeating the measurements gave a positive test-retest reliability coefficient of r = .84 (p < .001) and r = .64 (p < .001) for teacher and parent reports, respectively. The results indicate that both proxy reports can be useful tools in assessing MVPA in young children but that leisure-time activity reports provide a better basis for extrapolation in assessing weekly MVPA.
Cellular Immune Response to Anaerobic Exercise among Gymnasts and Untrained Girls
Authors: Wolach Baruch , Falk Bareket , Kodesh Einat , Radnay Judith , Shapiro Hava , Yarom Yonathan , Eliakim Alon
Published: August 2016

The purpose of the present study was to investigate the effect of anaerobic exercise on aspects of cellular immune function among 10–12-year-old highly trained female gymnasts (n = 7) compared with age- and maturity-matched untrained girls (n = 6). Blood samples were drawn before, immediately after, and 24 hr following exercise. Leukocyte number, particularly neutrophils and lymphocytes, increased following 30 s of supramaximal exercise and returned to baseline values following 24 hr in both groups. Total T-cell and B-cell concentrations, as well as T-helper (CD4) and T-suppressor (CD8) number increased immediately after exercise and decreased following 24 hr in both groups. The CD4:CD8 ratio was reduced following exercise mainly due to an increase in CD8. Natural killer cell count was elevated following exercise and continued to be elevated 24 hr following exercise in both groups. In summary, the exercise-induced changes in cellular immune function among both groups were similar to changes described in adults.
Muscle Function of 11- to 17-Year-Old Children of Extremely Low Birthweight
Authors: Small Eric , Bar-Or Oded , Van Mil Edgar , Saigal Saroj
Published: August 2016

This study compared the anaerobic performance and the muscle strength between extremely low birthweight (> 1,000 g = ELBW) 11- to 17-year-old adolescents and normal birthweight (< 2,500 g = NEW) controls. Seventeen ELBW (9 females and 8 males) and 17 NEW (9 females and 8 males) subjects took part. ELBW had lower anaerobic performance, as manifested in mean (p = .03) and peak (p < .001) mechanical power per kg body mass (Wingate Anaerobic Test). In absolute units mean power and peak power tended (p = .06 and .08, respectively) to be lower in the ELBW group, but there were no inter-group differences in the isokinetic strength of knee extensors or flexors (Kin Com dynamometer). ANOVA revealed no interaction between the effects of low birthweight and gender. We propose that dynamic, but not static, muscle performance in ELBW is still somewhat inferior in adolescence. This may reflect deficient neuromuscular control.
Using a Facemask and Sealant to Measure Respiratory Gas Exchange in Children during Exercise
Authors: Mahon Anthony D. , Stolen Kira Q. , Gay Julie A.
Published: August 2016

The purpose of this study was to compare the cardiorespiratory responses during treadmill exercise in 19 children (age, 10.5 ± 1.6 years) wearing a facemask and sealant versus a mouthpiece and nose clip. Cardiorespiratory responses were measured at 80.4 m · min−1, 134.0 m · min−1 and at peak exercise during two separate exercise tests. During the facemask trial, VO2 (ml · kg−1 min−1) was 16.9 ±3.1 at 80.4 m · min−1, 36.2 ± 3.9 at 134.0 m · min−1, and 49.5 ± 5.6 at peak exercise. During the mouthpiece trial, VO2 was 17.2 ± 2.8,36.7 ± 3.9, and 49.9 ± 5.2, respectively. VE (L · min−1) at the three intensities were 13.6 ± 2.2, 34.3 ± 5.7, and 56.5 ±11.1 for the facemask trial and 13.2 ± 1.6, 33.4 ± 5.0, and 54.8 ± 11.9 for the mouthpiece trial, respectively. Differences between trials were not significant. Intraclass correlations between the trials for VO2, (ml · kg −1 · min−1) ranged from R = 0.83 while walking to R = 0.95 at peak exercise; for VE, the intraclass correlations ranged from R = 0,63 to R = 0.91. In conclusion, die use of a facemask and sealant during exercise testing in this age group produced comparable results to those obtained using a mouthpiece and nose clip, and was more preferred.
Validation of an Electronic Pedometer for Measurement of Physical Activity in Children
Authors: Kilanowski Colleen K. , Consalvi Angela R. , Epstein Leonard H.
Published: August 2016

Activity measurement using a uniaxial electronic pedometer was compared to a triaxial accelerometer and behavioral observation measurements for ten 7−12-year-old children studied during high intensity recreational and low intensity classroom periods. Correlations between all measures were significant for recreational and classroom periods combined, and recreational periods alone (r’s > .90, p < .001). Correlations between the pedometer and accelerometer were significantly lower during classroom versus recreational activities (0.98 vs. 0.50, p < .05). This may be due in part to the uniaxial pedometer being sensitive only to vertical and not back and forward or side to side movement.
Children’s Physical Activity Choices: A Developmental Analysis of Gender, Intensity Levels, and Time
Authors: Hovell Melbourne F. , Sallis James F. , Kolody Bohdan , McKenzie Thomas L.
Published: August 2016

Students’ (n = 1,041) physical activity choices were assessed during the fourth and sixth grades for weekdays, weekends, and summer vacations. Activities were summarized for boys and girls by intensity, individual versus team, and for selected classes. Boys performed more team activities and reported more overall physical activity. Boys and girls decreased their participation in individual physical activities. Students decreased in total energy expended for all time periods. Decreasing activity level and selection of fewer individual activities make lifetime exercise unlikely. Results suggest that children become less active than recommended for health promotion before completing elementary school.
Clustering of Lifestyle CVD Risk Factors and Its Relationship with Biological CVD Risk Factors
Authors: Kilkens Olga J.E. , Gijtenbeek Britt A.J. , Twisk Jos W.R. , van Mechelen Willem , Kemper Han C.G.
Published: August 2016

The purpose of this study was (a) to investigate whether lifestyle risk factors cluster and (b) to investigate the influence of this clustering on biological CVD risk factors. This study was part of the Amsterdam Growth and Health Study (AGHS), an observational longitudinal study in which 6 repeated measurements were carried out on 181 13-year-old subjects over a period of 15 years. A longitudinal analysis (carried out with generalized estimating equations) showed no significant clustering of lifestyle risk factors at the population level. For each subject at each separate measurement period, lifestyle risk factors were summed to form a cluster score. A longitudinal linear regression analysis showed no significant relationship between the cluster score and biological CVD risk factors, except for a significant inverse relationship with cardiopulmonary fitness. In general, however, the results did not support the assumption that clustering of unhealthy lifestyle is related to biological CVD risk factors.
Short Longitudinal Study of Boys Playing Soccer: Parental Height, Birth Weight and Length, Anthropometry, and Pubertal Maturation in Elite and Non-Elite Players
Authors: Hansen Lone , Klausen Klaus , Bangsbo Jens , Müller Jørn
Published: August 2016

Ninety-eight young male soccer players were investigated for differences between elite players (E) and non-elite players (NE) in height, weight, BMI, skinfold, maturation, genetic potential for height, and birth weight and length. The subjects were included in the study at the age of 10-12 years and then examined three times with half-year intervals. Maturation was evaluated by testicular volumes. In addition, serum testosterone and insulin-like growth factor-I were measured. Adjustment for age was carried out because of a difference in age (11.9 [E] vs. 11.6 [NE] years) between the two groups. The players selected for the elite group were taller (152.7, 155.7, and 160 cm (E) vs. 147.4, 150.1, and 154.3 cm (NE), p = .015; MANOVA), had lower values for skinfolds (27.6, 28.3, and 27.5 mm (E) vs. 33.7, 35.1, and 36.1 mm (NE), p = .005), and greater testicular volume, compared with non-elite players (5.8, 7.6, and 9.3 ml (E) vs. 3.9, 5.0, and 6.6 ml (NE), p < .05). A tendency for higher values of serum testosterone in the elite group was present (p = .076), but no difference in IGF-I was found (p = .796). No differences in the genetic constitution for height was found. The present data shows that young soccer players selected for the best teams are taller, leaner, and more mature compared to young soccer players at a lower level.
Validity of Heart Rate, Pedometry, and Accelerometry for Estimating the Energy Cost of Activity in Hong Kong Chinese Boys
Authors: Louie Lobo , Eston Roger G. , Rowlands Ann. V. , Tong Kwok Keung , Ingledew David K. , Fu Frank H.
Published: August 2016

This study compared the accuracy of heart rate monitoring, pedometry, and uniaxial and triaxial aecelerometry for estimating oxygen consumption during a range of activities in Hong Kong Chinese boys. Twenty-one boys, aged 8–10 years, walked and ran on a treadmill, played catch, played hopscotch, and sat and crayoned. Heart rate, uniaxial and triaxial accelerometry counts, pedometry counts, and scaled oxygen uptake (SVO2) were measured. All measures correlated significantly with VO2 scaled to body mass−0.75 (SVO2). The best predictor of SVO2 was triaxial accelerometry (R2 = 0.89). Correlations in this study were comparable with those in a previous study that used identical methods on 30 UK boys and girls. These results provide further confirmation that triaxial accelerometry provides the best assessment of energy expenditure and that pedometry offers potential for large population studies.
Physiological Determinants of Maximal Aerobic Power in Healthy 12-Year-Old Boys
Authors: Rowland Thomas , Kline Gregory , Goff Donna , Martel Leslie , Ferrone Lisa
Published: August 2016

Little is known regarding the physiological determinants of maximal oxygen uptake (VO2max) in children. A group of 39 healthy sixth-grade boys (mean age, 12.2 years) underwent maximal cycle testing with determination of cardiovascular factors using Doppler echocardiography as well as standard gas exchange variables. Maximal stroke index was related to VO2max/kg (r=0.52, p < .05), but no relationship was observed between VO2max/kg and either maximal heart rate or calculated maximal arteriovenous oxygen difference. Values of maximal stroke index were closely related to those at rest (r = 0.67). These findings suggest that factors influencing resting stroke volume are primarily responsible for inter-individual differences in VO2max per kg in healthy, non-athletically-trained boys.
Validity of the Previous Day Physical Activity Recall (PDPAR) in Fifth-Grade Children
Authors: Trost Stewart G. , Ward Dianne S. , McGraw Ben , Pate Russell R.
Published: August 2016

This study evaluated the validity of the Previous Day Physical Activity Recall (PDPAR) self-report instrument in quantifying after-school physical activity behavior in fifth-grade children. Thirty-eight fifth-grade students (mean age, 10.8 ± 0.1; 52.6% female; 26.3% African American) from two urban elementary schools completed the PDPAR after wearing a CSA WAM 7164 accelerometer for a day. The mean within-subject correlation between self-reported MET level and total counts for each 30-min block was 0.57 (95% C.I., 0.51–0.62). Self-reported mean MET level during the after-school period and the number of 30-min blocks with activity rated at ≥ 6 METs were significantly correlated with the CSA outcome variables. Validity coefficients for these variables ranged from 0.35 to 0.43 (p < .05). Correlations between the number of 30-min blocks with activity rated at ≥ 3 METs and the CSA variables were positive but failed to reach statistical significance (r = 0.19–0.23). The PDPAR provides moderately valid estimates of relative participation in vigorous activity and mean MET level in fifth-grade children. Caution should be exercised when using the PDPAR to quantify moderate physical activity in preadolescent children.
Tracking of Physical Activity, Physical Inactivity, and Health-Related Physical Fitness in Rural Youth
Authors: Pate Russell R. , Trost Stewart G. , Dowda Marsha , Ott Alise E. , Ward Dianne S. , Saunders Ruth , Felton Gwen
Published: August 2016

This study examined the tracking of selected measures of physical activity, inactivity, and fitness in a cohort of rural youth. Students (N = 181, 54.7% female, 63.5% African American) completed test batteries during their fifth- (age = 10.7 ± 0.7 years), sixth-, and seventh-grade years. The Previous Day Physical Activity Recall (PDPAR) was used to assess 30-min blocks of vigorous physical activity (VPA), moderate-to-vigorous physical activity (MVPA), TV watching and other sedentary activities, and estimated energy expenditure (EE). Fitness measures included the PWC 170 cycle ergometer test, strength tests, tnceps skinfold thickness, and BMI. Intraclass correlation coefficients (ICCs) for VPA, MVPA, and after-school EE ranged from 0.63 to 0.78. ICCs ranged from 0.49 to 0.71 for measures of inactivity and from 0.78 to 0.82 for the fitness measures. These results indicate that measures of physical activity, inactivity, and physical fitness tend to track during the transition from elementary to middle school.
Risks and Benefits of Youth Sport Specialization: Perspectives and Recommendations
Authors: Wiersma Lenny D.
Published: August 2016

Of growing concern to sport researchers is the practice of youth sport athletes specializing in sport at a young age. Sport specialization is characterized by year-round training in a single sport at the exclusion of other sport or nonsport activities. The purpose of this paper is to discuss the potential benefits of specialized sport at an early age in light of the potential risks associated with specialized participation. Three areas of consideration are discussed, including motor skill acquisition and performance, potential sociological consequences, and psychological concerns related to high-intensity training of young athletes. Finally, recommendations for further research and practical considerations are suggested for deciding the appropriateness of specialized sport in the training and development of youth sport athletes.
Training Practices and Staleness in 13–18-Year-Old Swimmers: A Cross-Cultural Study
Authors: Raglin John , Sawamura Sachi , Alexiou Serafim , Hassmén Peter , Kenttä Goran
Published: August 2016

Adolescent swimmers (N = 231) from Greece, Japan, Sweden, and the U.S. completed questionnaires on training practices, mood state, staleness prevalence, and symptoms. Contrasts were made across countries and between stale and healthy groups. Of the total sample, 34.6% reported having been stale, ranging from 20.5% to 45.1% across countries. The mean length of staleness episodes was 3.6 weeks. Stale swimmers had faster (p < .01) personal best times in the 100-m freestyle compared with healthy swimmers. Mood disturbance was elevated (p < .05) during peak training for all countries except Japan. Stale swimmers reported greater (p < .05) mood disturbance at all assessments compared with healthy swimmers. The pattern of staleness symptoms was similar across all countries, with perception of training effort being the most affected.
Correlates of Physical Activity in Male and Female Youth
Authors: Bungum Timothy , Dowda Marsha , Weston Anne , Trost Stewart G. , Pate Russell R.
Published: August 2016

This study examined associations between psychosocial factors and physical activity in a group of youth (n = 520). Students completed the Previous Day Physical Activity Recall and a survey of potential determinants of physical activity. Regression analyses of intentions to be physically active revealed that enjoyment and self-efficacy predicted intentions for both males and females. Attitudes predicted moderate to vigorous activity (MVPA), and enjoyment and self-efficacy predicted vigorous activity (VPA) for males. Self-efficacy predicted both MVPA and VPA for females. The findings suggest that intervention programs targeted at youth should include developmentally appropriate activities that are fun and promote physical activity self-efficacy.