Effect of postural changes on 3D joint angular velocity during starting block phase

Abstract

Few studies have focused on the effect of posture during sprint start. The aim of this study was to measure the effect of the modification of horizontal distance between the blocks during sprint start on three dimensional (3D) joint angular velocity. Nine trained sprinters started using three different starting positions (bunched, medium and elongated). They were equipped with 63 passive reflective markers, and an opto-electronic Motion Analysis® system was used to collect the 3D marker trajectories. During the pushing phase on the blocks, norm of the joint angular velocity (NJAV), 3D Euler angular velocity (EAV) and pushing time on the blocks were calculated. The results demonstrated that the decrease of the block spacing induces an opposite effect on the angular velocity of joints of the lower and the upper limbs. The NJAV of the upper limbs is greater in the bunched start, whereas the NJAV of the lower limbs is smaller. The modifications of NJAV were due to a combination of the movement of the joints in the different degrees of freedom. The medium start seems to be the best compromise because it leads, in a short pushing time, to a combination of optimal joint velocities for upper and lower segments.     

Parental child abuse potential and subsequent coping competence in disadvantaged preschool children: moderating effects of sex and ethnicity

This study evaluated the effects of abuse potential in parents on subsequent coping competence domains in their children, using a model empirically supported in a high-risk community sample by Moreland and Dumas (2007). Data from an ethnically diverse sample of 579 parents enrolled in the PACE (Parenting Our Children to Excellence) program was used to evaluate whether parental child abuse potential assessed at pre-intervention negatively contributed to child affective, achievement, and social coping competence in preschoolers one year later, and whether these associations were moderated by sex or ethnicity. Cross-sectional results indicated that parental child abuse potential was negatively related to child affective and achievement coping competence, after accounting for variance associated with child behavior problems. However, child abuse potential was not predictive of subsequent coping competence in any domain after controlling for previous levels of child coping competence. No moderating effects were found for sex and ethnicity, but results showed main effects of sex and ethnicity in cross-sectional analyses. Clinical implications and future directions are discussed.     

Behavioral and Contextual Manifestations of Parenting Stress in Mother-Child Dyads

Extensive data from mother-child interaction in the laboratory, teacher reports of child behavior problems in the preschool and maternal reports of child behavior problems, marital satisfaction, depression, social insularity, and other contextual risk factors were used to (1) describe the behavioral and contextual manifestations of parenting stress, (2) empirically investigate different cutoff points using the Parenting Stress Index (PSI; Abidin, 1990), and (3) validate a new French translation of the PSI Groups of mothers were formed on the basis of PSI percentile scores using cutoffs of 90% (Very High), 80-90% (High), 20-80% (Average) and 0-20% (Low) in order to determine the levels of parenting stress associated with the various risk factors assessed. Base rates and conditional probabilities were calculated to assess the extent to which mother and child responded contingently to each other's behaviors and affect during a problem-solving task . Results showed that (1) maternal behavior was more associated with total parenting stress than child behavior. (2) parenting stress was clearly associated with child's behavior problems in the home and classroom; (3) parenting stress was consistently associated with other risk factors; and (4) very highly stressed mothers appeared to be at significantly greater risk than high stressed mothers in terms of their social adaptation and emotional well being, as well as that of their preschool children.