The effect of crank rate strategy on peak aerobic power and peak physiological responses during arm crank ergometry

The main aim of this study was to determine whether the use of an imposed or freely chosen crank rate would influence submaximal and peak physiological responses during arm crank ergometry. Fifteen physically active men participated in the study. Their mean age, height, and body mass were 25.9 (s = 6.2) years, 1.80 (s = 0.10) m, and 78.4 (s = 6.1) kg, respectively. The participants performed two incremental peak oxygen consumption (VO(2peak)) tests using an electronically braked ergometer. One test was performed using an imposed crank rate of 80 rev x min(-1), whereas in the other the participants used spontaneously chosen crank rates. The order in which the tests were performed was randomized, and they were separated by at least 2 days. Respiratory data were collected using an on-line gas analysis system, and fingertip capillary blood samples ( approximately 20 microl) were collected for the determination of blood lactate concentration. Heart rate was also recorded throughout the tests. Time to exhaustion was measured and peak aerobic power calculated. Submaximal data were analysed using separate two-way repeated-measures analyses of variance, while differences in peak values were analysed using separate paired t-tests. Variations in spontaneously chosen crank rate were assessed using a one-way analysis of variance with repeated measures. Agreement between the crank rate strategies for the assessment of peak values was examined by calculating intra-class correlation coefficients (ICC) and 95% limits of agreement (95% LoA). While considerable between-participant variations in spontaneously chosen crank rate were observed, the mean value was not different (P > 0.05) from the imposed crank rate of 80 rev x min(-1) at any point. No differences (P > 0.05) were observed for submaximal data between crank strategies. Furthermore, mean peak minute power [158 (s = 20) vs. 158 (s = 18) W], time to exhaustion [739 (s = 118) vs. 727 (s = 111) s], and VO(2peak)[3.09 (s = 0.38) vs. 3.04 (s = 0.34) l x min(-1)] were similar for the imposed and spontaneously chosen crank rates, respectively. However, the agreement for the assessment of VO(2peak) (ICC = 0.78; 95% LoA = 0.04 +/- 0.50 l x min(-1)) between the cranking strategies was considered unacceptable. Our results suggest that either an imposed or spontaneously chosen crank rate strategy can be used to examine physiological responses during arm crank ergometry, although it is recommended that the two crank strategies should not be used interchangeably.     

Effect of stroke rate on the distribution of net mechanical power in rowing

The aim of this study was to assess the effect of manipulating stroke rate on the distribution of mechanical power in rowing. Two causes of inefficient mechanical energy expenditure were identified in rowing. The ratio between power not lost at the blades and generated mechanical power (P(rower)) and the ratio between power not lost to velocity fluctuations and P(rower) were used to quantify efficiency (e(propelling) and e(velocity) respectively). Subsequently, the fraction of P(rower) that contributes to the average velocity (chi(boat)) was calculated (e(net)). For nine participants, stroke rate was manipulated between 20 and 36 strokes per minute to examine the effect on the power flow. The data were analysed using a repeated-measures analysis of variance. Results indicated that at higher stroke rates, P(rower), chi(boat), e(propelling), and e(net) increase, whereas e(velocity) decreases (P < 0.0001). The decrease in e(velocity) can be explained by a larger impulse exchange between rower and boat. The increase in e(propelling) can be explained because the work at the blades decreases, which in turn can be explained by a change in blade kinematics. The increase in e(net) results because the increase in e(propelling) is higher than the decrease in e(velocity). Our results show that the power equation is an adequate conceptual model with which to analyse rowing performance.     

Consistency of performances in the Tkatchev release and re-grasp on high bar

The Tkatchev on the high bar is a release and re-grasp skill in which the gymnast rotates in a direction during flight opposite to that of the preceding swing. Since the release window is defined as the time during which the gymnast has appropriate linear and angular momentum to ensure the bar can be re-grasped, it was speculated that the release windows for this skill would be smaller than for dismounts that are less constrained. One senior male gymnast competing at national standard performed 60 Tkatchev trials. A four-segment planar simulation model of the gymnast and high bar was used to determine the release windows in 10 successful and 10 unsuccessful performances of the Tkatchev recorded using a Vicon motion analysis system. Model parameters were optimized to obtain a close match between simulations and recorded performances in terms of rotation angle (1 degree), bar displacements (0.01 m), and release velocities (1%). Each matched simulation was used to determine the time window around the actual point of release for which the model had appropriate release parameters to complete the Tkatchev successfully. The release windows for the successful trials were small compared with those of dismounts. The unsuccessful trials were associated with later release and later timing of the actions at the shoulders and hips.     

Assessing preschool children's physical activity: the Observational System for Recording Physical Activity in children-preschool version

In this paper we present initial information concerning a new direct observation system-the Observational System for Recording Physical Activity in Children-Preschool Version. The system will allow researchers to record young children's physical activity levels while also coding the topography of their physical activity, as well as detailed indoor and outdoor social and nonsocial contextual information. With respect to interobserver agreement (IOA), the kappa and category-by-category agreement mean of those obtained for the three illustrative preschools were generally above .80. Hence, our IOA data indicated that trained observers in the three preschools frequently agreed on the eight observational categories and accompanying codes. The results for preschoolers' level of physical activity indicated they spent the majority of observational intervals in sedentary activity (i.e., more than 80% intervals) and were observed in moderate to vigorous physical activity much less frequently (i.e., 5% or fewer intervals). For the 15 indoor and 12 outdoor activity contexts, variability across both the activity contexts and the three preschools were evident. Nevertheless, three classroom contexts-transition, snacks, and naptime--accounted for the greatest porportion of coded activity contexts for the children. In the three preschools, 4 of 17 physical activity types--sit and squat, lie down, stand, and walk--accounted for the topography of much of children's physical activity behavior Systematic observation of more representative preschool samples might better inform our present understanding of young children's physical activity in community preschool programs.     

Social Groups and Children’s Intergroup Attitudes: Can School Norms Moderate the Effects of Social Group Norms?

The effects of social group norms (inclusion vs. exclusion vs. exclusion-plus-relational aggression) and school norms (inclusion vs. no norm) on 7- and 10-year-old children's intergroup attitudes were examined. Children (n = 383) were randomly assigned to a group with an inclusion or exclusion norm, and to 1 of the school norm conditions. Findings indicated that children's out-group attitudes reflected their group's norm but, with increasing age, they liked their in-group less, and the out-group more, if the group had an exclusion norm. The school inclusion norm instigated more positive attitudes toward out-group members, but it did not moderate or extinguish contrary group norms. The use of school norms to counteract the effects of children's social group norms is discussed.     

Reporter discrepancies among parents, adolescents, and peers: adolescent attachment and informant depressive symptoms as explanatory factors

The issue of informant discrepancies about child and adolescent functioning is an important concern for clinicians, developmental psychologists, and others who must consider ways of handling discrepant reports of information, but reasons for discrepancies in reports have been poorly understood. Adolescent attachment and informant depressive symptoms were examined as 2 explanations for absolute and directional discrepancies about adolescent symptoms, relationships, and social behavior in a sample of 189 eleventh-grade students (mean age=16.5 years). Adolescent attachment predicted absolute discrepancies, with greater attachment coherence associated with fewer discrepancies in reports of adolescent depressive symptoms, parent-adolescent conflict, and adolescent externalizing behavior. Parents' but not adolescents' depressive symptoms sometimes predicted absolute discrepancies. Mothers' depressive symptoms and adolescent attachment predicted the direction of discrepancies for mother-peer reports only.     

A randomized controlled trial of Child FIRST: a comprehensive home-based intervention translating research into early childhood practice

This randomized, controlled trial was designed to document the effectiveness of Child FIRST (Child and Family Interagency, Resource, Support, and Training), a home-based, psychotherapeutic, parent-child intervention embedded in a system of care. Multirisk urban mothers and children, ages 6-36 months (N = 157) participated. At the 12-month follow-up, Child FIRST children had improved language (odds ratio [OR] = 4.4) and externalizing symptoms (OR= 4.7) compared to Usual Care children. Child FIRST mothers had less parenting stress at the 6-month follow-up (OR = 3.0), lower psychopathology symptoms at 12-month follow-up (OR = 4.0), and less protective service involvement at 3 years postbaseline (OR = 2.1) relative to Usual Care mothers. Intervention families accessed 91% of wanted services relative to 33% among Usual Care. Thus, Child FIRST is effective with multirisk families raising young children across multiple child and parent outcomes.     

The significance of insecure and disorganized attachment for children's internalizing symptoms: a meta-analytic study

This meta-analytic review examines the association between attachment and internalizing symptomatology during childhood, and compares the strength of this association with that for externalizing symptomatology. Based on 42 independent samples (N = 4,614), the association between insecurity and internalizing symptoms was small, yet significant (d = 0.15, CI 0.06~0.25) and not moderated by assessment age of internalizing problems. Avoidance, but not resistance (d = 0.03, CI -0.11~0.17) or disorganization (d = 0.08, CI -0.06~0.22), was significantly associated with internalizing symptoms (d = 0.17, CI 0.03~0.31). Insecurity and disorganization were more strongly associated with externalizing than internalizing symptoms. Discussion focuses on the significance of attachment for the development of internalizing versus externalizing symptomatology.     

Components and context: exploring sources of reading difficulties for language minority learners and native english speakers in urban schools

Drawing on the cognitive and ecological domains within the componential model of reading, this longitudinal study explores heterogeneity in the sources of reading difficulties for language minority learners and native English speakers in urban schools. Students (N = 150) were followed from first through third grade and assessed annually on standardized English language and reading measures. Structural equation modeling was used to investigate the relative contributions of code-related and linguistic comprehension skills in first and second grade to third grade reading comprehension. Linguistic comprehension and the interaction between linguistic comprehension and code-related skills each explained substantial variation in reading comprehension. Among students with low reading comprehension, more than 80% demonstrated weaknesses in linguistic comprehension alone, whereas approximately 15% demonstrated weaknesses in both linguistic comprehension and code-related skills. Results were remarkably similar for the language minority learners and native English speakers, suggesting the importance of their shared socioeconomic backgrounds and schooling contexts.