Effect of sleep deprivation on diurnal variation of vertical perception and postural control.

The aim of the study was to test the effect of total sleep deprivation on performance and time-of-day pattern of subjective visual vertical (SVV) and postural control. Nineteen healthy, young participants (4 women and 15 men 21.9 ± 1.2 yr) were engaged in two counterbalanced experimental sessions with or without total sleep deprivation. Oral temperature, Karolinska Sleepiness Scale, and visual analogic scale for fatigue, postural control, and SVV were randomly measured every 4 h, from 0600 to 2200. A linear mixed model was used to capture the effect of time of day and sleep condition as factors. A classical adjusted COSINOR function was then used to modelize this daily variation. After the control night of sleep, SVV as well as oral temperature, sleepiness, and fatigue showed significant time-of-day variation, contrasting with measures of postural control which remained stable across the day. After sleep deprivation, SVV showed no diurnal variation, but its mean deviation value increased by 29%. Postural control capability also decreased after sleep deprivation, with a higher center of pressure surface (+70.4%) and total length (+7.37%) but remained stable throughout the day. These results further confirm the negative effect of sleep loss on postural control capability. Even if a direct relationship cannot be confirmed, the disruption of SVV capacity after sleep deprivation could strongly play a role in postural control capacity changes. Sleep deprivation should be considered as a potent factor involved in balance loss and subsequent fall. NEW & NOTEWORTHY The topic of sleep deprivation and postural control is not understood, with discrepancy among results. This study described that postural control displays a stable level throughout the day and that sleep deprivation, even if it increases postural sway, does not affect this stable diurnal pattern. The modification of the perception of the vertical level after sleep deprivation could strongly play a role in the observed changes in postural control capacity.

Age- and gender-related development of stretch shortening cycle during a sub-maximal hopping task.

The aim of this study was to analyse the effects of age and gender (and their interaction) on a stretch shortening cycle solicited during a hopping task. For this aim, 147 girls and 148 boys aged 11 to 20 years, who were enrolled in middle school or secondary school with no experience in sport activity, or training less than three times per week, performed 3×5 hops in place. Leg-stiffness, jump-height and reactive-strength indices were assessed using an accelerometer (Myotest). The participants were selected in order to form five age groups: 11 12, 13-14, 15-16, 17-18 and 19-20 years. Regression analysis between force and centre of mass displacement revealed spring-mass behaviour for all groups (r(2)=.73-.89), meaning that beginning at the age of 11 years, children are able to perform complex inter-muscular coordination of the lower limbs, revealing efficient neural control early in childhood. Leg stiffness increased from 24.7 ± 10.6 kN · m(-1) at 11-12 years to 44.1 ± 14 kN · m(-1) in boys, with a small increase until 16 years (+17%) and a large increase between 17 and 20 years (+32.7%). In girls, leg stiffness increased from 26.6 ± 9 kN · m(-1) at 11-12 years to 39.4 ± 10.9 kN · m(-1) at 19-20 years, with a curious decrease in leg stiffness at 17-18 years, probably due to an increase in the percentage of fat at this age (25%). While no gender effect was found, the reactive-strength index revealed that, from 15-16 years onward, boys were better able to produce high levels of force in a shorter time than girls. The age of 15-16 years is a threshold of maturity and gender differentiation, where the boys investigated are more efficient in the stretch shortening cycle.

Development of information-movement couplings in a rhythmical ball-bouncing task: from space- to time-related information.

We studied the development of information-movement couplings in a ball-bouncing task with a special interest in how space- and time-related information is used by people of different ages. Participants from four age groups (children aged 7-8, 9-10 and 11-12 years, and adults) performed a virtual ball-bouncing task in which space- and time-related information were independently manipulated. Task performance and information-movement couplings were analyzed. Our results confirm a clear use of time-related information in adults, while children demonstrated a predominant relationship between space-related information and the period of movement. In the course of development, however, the children become progressively more capable of using time-related information in order to control the rhythmic ball-bouncing task. A second and weaker coupling, between ball height information and racket velocity at impact, also appears in the course of development. The data seem to show that the development of children follows the freezing-freeing-exploiting sequence proposed by Savelsbergh and Van der Kamp (Int J Sport Psychol 31:467-484, 2000), with a significant change in how information is used to control movement related to age.

Effects of tennis practice on the coincidence timing accuracy of adults and children.

This study examines the development of perceptuomotor processes involved in coincidence timing tasks according to age and experience in tennis. Tennis players and novices, 7, 10, 13, and 23 years of age, were tested in a coincidence timing task which consisted of estimating the arrival of a simulated moving object on a target. The effect of three different motions were analyzed: constant velocity, constant acceleration, and constant deceleration. Results showed that (1) timing accuracy improves mainly between the ages of 7 and 10 years; (2) tennis practice accelerates the development of timing accuracy; and (3) acceleration or deceleration of the moving stimulus had no effect on the timing accuracy of any of the tested groups, suggesting a continuous visual control of the trajectory. Theoretical implications for the development of perceptuomotor processes involved in coincidence timing tasks are discussed.