The influence of ventilatory control on heart rate variability in children

The aim of this study was to determine the influence of breathing frequency and tidal volume on resting heart rate variability in children aged 9 years (n = 29) and 16 years (n = 19). Heart rate variability was measured in four conditions: (1) without the control of ventilation followed at random by (2) a fixed breathing frequency of 12 breaths x min(-1), (3) a breathing frequency of 12 breaths x min(-1) but with a fixed tidal volume of 30% vital capacity and (4) a fixed breathing frequency of 6 breaths x min(-1) and a tidal volume of 30% vital capacity. A total of 128 RR intervals (the time between two spikes in the heart rate) were detected and absolute high- and low-frequency spectral components were calculated using autoregressive modelling. The younger children were unable to control ventilation to achieve conditions 3 and 4; therefore, a 2 x 2 (group x condition) analysis of variance was used to analyse conditions 1 and 2. There were significant interactions between group and heart rate variability conditions for the low-frequency component and the ratio of low to high frequencies (P < 0.001). The main effect for condition showed that at 12 breaths x min(-1) with no fixed tidal volume there was a significantly higher standard deviation of the RR interval, total power and high-frequency (P< 0.01) and low-frequency spectral components (P < 0.05) than in the condition with no ventilatory control. Across the four breathing conditions for the older participants, the high-frequency spectral component was significantly higher in the condition at 6 breaths x min(-1) with a fixed tidal volume than in that with no ventilatory control (P < 0.005); the ratio of high to low frequencies was significantly lower for the spontaneous condition than those performed at 12 breaths x min(-1) (P < 0.001). The results provide evidence of the need for ventilatory control when assessing short-term resting heart rate variability in children.     

Age-related differences in vision and proprioception in a lower limb interceptive task: the effects of skill level and practice

This study examined age-related differences in the role of visual proprioception during a lower limb interceptive action and how this varies as a function of skill and practice. In Experiment 1, skilled and less-skilled 8-, 10-, and 12-year-old boys controlled a soccer ball using their preferred foot under full vision and when sight of the effector was occluded. With the exception of the high-skilled 12-year-olds and low-skilled 8-year-olds, participants showed a decrement in peformance when denied access to visual proprioception. In Experiment 2, the effect of practicing under different informational constraints was examined for 12 year-old boys. Children performed varying amounts of practice under full vision, or in a condition where sight of the foot was occluded, before being transferred to the alternative viewing condition. Participants who practiced under occluded viewing conditions showed greater relative improvement in performance over practice and transfer sessions compared with a full vision control group. Some support is provided for the manipulation of visual informational constraints as an effective pedagogical approach to motor learning.     

The Loughborough Intermittent Shuttle Test: a field test that simulates the activity pattern of soccer

The aims of this study were to describe and determine the test-retest reliability of an exercise protocol, the Loughborough Intermittent Shuttle Test (the LIST), which was designed to simulate the activity pattern characteristic of the game of soccer. The protocol consisted of two parts: Part A comprised a fixed period of variable-intensity shuttle running over 20 m; Part B consisted of continuous running, alternating every 20 m between 55% and 95% VO2max, until volitional fatigue. Seven trained games players (age 21.5+/-0.9 years, height 182+/-2 cm, body mass 80.1+/-3.6 kg, VO2max 59.0+/-1.9 ml x kg(-1) x min(-1); mean +/- s(x)) performed the test on two occasions (Trial 1 and Trial 2), at least 7 days apart, to determine the test-retest reliability of the sprint times and running capacity. The physiological and metabolic responses on both occasions were also monitored. The participants ingested water ad libitum during the first trial, and were then prescribed the same amount of water during the second trial. The 15 m sprint times during Trials 1 and 2 averaged 2.42+/-0.04 s and 2.43+/-0.04 s, respectively. Run time during Part B was 6.3+/-2.0 min for Trial 1 and 6.1+/-1.3 min for Trial 2. The 95% limits of agreement for sprint times and run times during Part B were -0.14 to 0.12 s and -3.19 to 2.16 min respectively. There were no differences between trials for heart rate, rating of perceived exertion, body mass change during exercise, or blood lactate and glucose concentrations during the test. Thus, we conclude that the sprint times and the Part B run times were reproducible within the limits previously stated. In addition, the activity pattern and the physiological and metabolic responses closely simulated the match demands of soccer.     

Evaluating carrascolendas: A television series for Mexican‐American children

Readers with young children may have noticed the occasional Spanish language vignettes appearing from time to time on Sesame Street, the popular public television program for pre‐schoolers. The following article describes the development and audience impact of a program designed to reach a Spanish‐American audience in a Texas city. The study is presented primarily as a guide for other programmers desiring to evaluate audience effects of such content. This article is a summary of a longer report done under an Office of Education subcontract to the Center for Communication Research at the University of Texas. Dr. Williams is Director of the Center and professor in the school of communications, while Diana Natalicio is now an assistant professor of linguistics at the University of Texas at El Paso after having completed her doctorate in linguistics at the Austin campus in 1970.     

Increased dietary carbohydrate and endurance during single-leg cycling using a limb with normal muscle glycogen concentration

The purpose of this study was to test the hypothesis that increased availability of blood-borne glucose would improve endurance after carbohydrate loading. A single-leg exercise model was employed, taking advantage of the fact that supercompensation of muscle glycogen occurs only in a previously exercised limb. Endurance time to exhaustion at 70% of maximal oxygen uptake (VO2 max) was determined for 11 males and three females who were then allocated to a control group or a high-carbohydrate (CHO) group. For 3 days following Test 1 the control group maintained a prescribed normal diet whilst the CHO group increased the proportion of energy derived from carbohydrate (62.1 +/- 4.3% cf. 43.9 +/- 2.0%, P less than 0.01). The endurance test was then repeated using the leg that was inactive during Test 1. Endurance time was increased on Test 2 (123.7 +/- 43.2 min cf. 98.5 +/- 21.9 min, P less than 0.05 one-tailed test) for the CHO group but not for the control group (101.8 +/- 21.7 min cf. 107.5 +/- 9.1 min, NS). There was no indication of enhanced carbohydrate metabolism during Test 2 for the CHO group but mean heart rate was lower during Test 2 than during Test 1 (145 +/- 14 beat min-1 cf. 152 +/- 12 beat min-1, P less than 0.05). These results suggest that the prior consumption of a high-carbohydrate diet improves endurance during high-intensity cycling with a limb with normal muscle glycogen concentration.