Differentiated ratings of perceived exertion at ventilatory threshold in children and adults

The purpose of this study was to examine overall, leg and chest ratings of perceived exertion (RPE) at ventilatory threshold (Th_vent) in 16 children (mean age 10.9 years) and 17 adults (mean age 24.3 years). Th_vent and maximum oxygen consumption (V˙O_{2 max} ) were measured during a graded exercise test on a cycle ergometer. Overall, leg and chest RPE were obtained at the end of each exercise stage. V˙O_{2 max} was 49.9 (8.5) and 47.1 (6.1) ml · kg⁻¹· min⁻¹ [mean (SD)] in the adults and children, respectively (P > 0.05). Relative to V˙O_{2 max} , Th_vent was 61.7 (5.3)% in the adults and 64.7 (5.2)% in the children (P > 0.05). Overall, leg, and chest RPE values at Th_vent for the adults were 11.5 (2.6), 11.9 (2.5), and 10.5 (2.5), while for the children these values were 13.6 (2.2), 14.1 (2.2), and 12.6 (2.3), respectively. All RPE values were higher for the children (P < 0.05). These results suggest that children are able to discriminate levels of exertion in different parts of their body during graded exercise. Furthermore, children rate an intensity corresponding to Th_vent to require a greater overall, leg and chest effort than adults exercising at a similar intensity. This indicates that children experience more pronounced cardiorespiratory and muscular sensations during this type of exercise. Accepted: 19 February 1998     

The measurement of resting metabolic rate in preschool children

Objective: This study examined the repeatability of measuring resting metabolic rate (RMR) in preschool children and the effect of different calculation protocols. Research Methods and Procedures: Eleven children (4 females and 7 males) participated in the project. They were recruited through advertisements in local schools and community centers. Resting metabolic rate was measured on 3 occasions over a 2‐week period, each after an overnight fast and each lasting ～20 to 25 minutes. Results were compared using repeated‐measures ANOVA to check for repeatability, and a number of methods of calculating RMR were assessed. Results: Repeatability of RMR measurements was good (coefficient of variation of replicates, 6.8%), with no significant difference between days of measurement. The lowest RMR measurement was obtained when the first 10 minutes were excluded and periods during which large activity was observed were excluded. This measurement was, on average, 4% lower than averaging the measurements after the first 5 minutes, including body movements. Discussion: This study suggests that RMR can be measured in preschool children and that the best method for calculating RMR in these subjects is to exclude periods when large body movements occur and the first 10 minutes of the measurement period. Only a single measurement of RMR is needed to obtain a reliable estimate.     

Sex and gender differences in secular trend of body size and frame indices of Lithuanians

In Lithuania, as in many other European countries, positive secular trend of body size became especially expressed at the middle of XX. century. The analysis showed the evident secular trend in height of adult Lithuanians since the end of XIX. century till 2001 from 163.5 till 181.3 cm in males and from 153.3 cm till 167.5 cm in females. Concerning growth and development of children, during the 1925-2001 period especially obvious acceleration of height was determined at the middle of adolescence due to much earlier sexual maturation at the end of XX. century. Secular trend of body height was more expressed in males of all ages, nevertheless this process stabilized in both sexes during the last decades. While comparing secular changes in BMI of adolescent Lithuanian girls and boys between the 1925-2001 period, the evident sexual differences in secular changes were determined from the middle of pubescence: the course of changes in BMI during the XX. century was nearly the same in both sexes, but at the end of XX. century older adolescent girls became obviously thinner compared with the changes of BMI in boys of the same age. A very similar trend in BMI of adult Lithuanian women since 1980 till 2002 was also detected. This phenomenon could be more related with the changes in life stile, modern-day canons for unrealistically thin female's body and strong social pressure on women today.     

Sex differences in the effect of birth order and parents’ educational status on stunting: A study on Bengalee preschool children from eastern India

One of the greatest problems facing developing countries, including rural India, is undernutrition in terms of stunting among under 5-year-old children. However, there exists scanty information on the prevalence of stunting among preschool children in India and in particular in West Bengal. This study investigated prevalence of stunting and identified the predictor(s) of stunting among 1-5-year-old Bengalee rural preschool children of Integrated Child Development Services (ICDS) centres. This cross-sectional study was undertaken at different ICDS centres of Chapra Block, Nadia District, West Bengal, India. A total of 673 preschool children (323 boys and 350 girls), aged 1-5 years were selected from 30 randomly selected ICDS centres to study the impact of parents’ educational status and child birth order on stunting. The overall (age and sex combined) rate of stunting was 39.2%. Child birth order (BO) (χ² = 14.10, df = 1, p < 0.001), father educational status (FES) (χ² = 21.11, p < 0.001) and mother educational status (MES) (χ² = 14.34, df = 1, p > 0.001) were significantly associated with the prevalence of stunting among girls. Logistic regression analyses revealed that both FES (Wald = 19.97, p < 0.001) as well as MES (Wald = 13.95, p < 0.001) were strong predictors of stunting among girls. Similarly BO (Wald = 13.71, p < 0.001) was a strong predictor of stunting among girls. Girls with ≥3rd BO had significantly higher risk (OR = 2.49, CI = 1.54-4.03) of stunting than those with ≤2nd BO. Moreover, girls with FES lower than secondary level had significantly (OR = 3.30, CI = 1.96-5.58) higher rate of stunting than those with FES ≥ secondary level. Similarly, girls with MES < secondary level had significantly (OR = 2.50, CI = 1.54-4.03) higher rate of stunting than those with FES ≥ secondary level.In conclusion our study revealed that BO as well as parents’ educational status were strong predictors of stunting among girls but not boys. Sex discrimination could be a likely cause for this sex difference in the impact of BO and parents’ educational status.     

Validation and calibration of an accelerometer in preschool children

Objective: Obesity rates in young children are increasing, and decreased physical activity is likely to be a major contributor to this trend. Studies of physical activity in young children are limited by the lack of valid and acceptable measures. The purpose of this study was to calibrate and validate the ActiGraph accelerometer for use with 3‐ to 5‐year‐old children. Research Methods and Procedures: Thirty preschool children wore an ActiGraph accelerometer (ActiGraph, Fort Walton Beach, FL) and a Cosmed portable metabolic system (Cosmed, Rome, Italy) during a period of rest and while performing three structured physical activities in a laboratory setting. Expired respiratory gases were collected, and oxygen consumption was measured on a breath‐by‐breath basis. Accelerometer data were collected at 15‐second intervals. For cross‐validation, the same children wore the same instruments while participating in unstructured indoor and outdoor activities for 20 minutes each at their preschool. Results: In calibrating the accelerometer, the correlation between V?o ₂ (ml/kg per min) and counts was r = 0.82 across all activities. The only significant variable in the prediction equation was accelerometer counts (R² = 0.90, standard error of the estimate = 4.70). In the cross‐validation, the intraclass correlation coefficient between measured and predicted V?o ₂ was R = 0.57 and the Spearman correlation coefficient was R = 0.66 (p < 0.001). Cut‐off points for moderate‐ and vigorous‐intensity physical activity were identified at 420 counts/15 s (V?o ₂ = 20 mL/kg per min) and 842 counts/15 s (V?o ₂ = 30 mL/kg per min), respectively. When these cutpoints were applied to the cross‐validation data, percentage agreement, kappa, and modified kappa for moderate activity were 0.69, 0.36, and 0.38, respectively. For vigorous activity, the same measures were 0.81, 0.13, and 0.62. Discussion: Accelerometer counts were highly correlated with V?o ₂ in young children. Accelerometers can be appropriately used as a measure of physical activity in this population.     

Cultural and national differences in the epidemiology of behavior problems of preschool children

Results from two epidemiological surveys, one British and the other American, examining the prevalence of behavior problems in preschool children are compared. Using the same interview technique, prevalence rates were found to be similar despite national, cultural and demographic differences. These surveys constitute the first stage in projects to examine the causes and persistence of childhood psychiatric disorder arising during the preschool years. The relevance of this work to anthropology is discussed.     

Influence of climate on heart rate in children: comparison between intermittent and continuous exercise

Heart rate (HR) monitoring is commonly used to assess 24-h energy expenditure (EE) in children but it has been found to overestimate the true values. One reason for this may be the effect of climatic heat stress on HR. An equation has been previously developed to adjust HR measured during continuous exercise for the influence of climate. Since play in children is rarely of a continuous pattern, one objective of this study was to compare the effects of climatic heat stress on the HR response to intermittent and to continuous exercise. A second objective was to determine whether the previously developed equation is suitable for intermittent exercise. A group of 12 boys and 8 girls (aged 8–11 years) cycled in a climatic chamber. The exercise consisted of continuous cycling for 5 min at 35%, 55%, and 75% of peak oxygen up take (random order) followed by alternating cycling at the same resistance and cadence (30 s) and rest (30 s) for 3 additional min. The oxygen uptake (V˙O₂) and HR were determined for 2 min at the end of continuous cycling and for 2 min during intermittent cycling. Climatic conditions (randomly assigned) were dry bulb temperature T _db 22°C, 50% relative humidity (rh); T _db 28°C, 55% rh; T _db 32°C, 52% rh; or T _db 35°C, 58% rh. The difference between HR measured at a given T _db (HR_meas) and HR at 22°C and at the same V˙O₂ was then calculated (ΔHR). The ΔHR increased linearly with increasing temperature but was not related to V˙O₂ or to exercise type. However, a small but significant difference was found if the published equation was used with data from intermittent exercise. The accuracy of the existing equation adjusting HR_meas for the influence of T _db (HR_corr) could be improved to HR_corr= HR_meas · (1.18308−(0.0083218 · T _db)). In conclusion, the effects of climatic heat stress on HR were similar in continuous and intermittent exercise, and HR can be adjusted for the influence of climate in groups of pre- and early pubertal children during rest, intermittent and continuous exercise at ambient temperatures between 22°C and 35°C, thereby reducing the error in predicting EE from HR. Accepted: 13 January 1998     

Sex differences in political leadership in an egalitarian society

We test the contribution of sex differences in physical formidability, education, and cooperation to the acquisition of political leadership in a small-scale society. Among forager-farmers from the Bolivian Amazon, we find that men are more likely to exercise different forms of political leadership, including verbal influence during community meetings, coordination of community projects, and dispute resolution. We show that these differences in leadership are not due to gender per se but are associated with men's greater number of cooperation partners, greater access to schooling, and greater body size and physical strength. Men's advantage in cooperation partner number is tied to their participation in larger groups and to the opportunity costs of women's intrahousehold labor. We argue these results highlight the mutual influence of sexual selection and the sexual division of labor in shaping how women and men acquire leadership.     

Electrocardiogram data mining based on frame classification by dynamic time warping matching

This paper presents an electrocardiogram (ECG) data mining scheme based on the ECG frame classification realised by a dynamic time warping (DTW) matching technique, which has been used successfully in speech recognition. We use the DTW to classify ECG frames because ECG and speech signals have similar non-stationary characteristics. The DTW mapping function is obtained by searching the frame from its end to start. A threshold is setup for DTW matching residual either to classify an ECG frame or to add a new class. Classification and establishment of a template set are carried out simultaneously. A frame is classified into a category with a minimal residual and satisfying a threshold requirement. A classification residual of 1.33% is achieved by the DTW for a 10-min ECG recording.     

Sex differences in rhesus monkey toy preferences parallel those of children

Sex differences in toy preferences in children are marked, with boys expressing stronger and more rigid toy preferences than girls, whose preferences are more flexible. Socialization processes, parents, or peers encouraging play with gender-specific toys are thought to be the primary force shaping sex differences in toy preference. A contrast in view is that toy preferences reflect biologically-determined preferences for specific activities facilitated by specific toys. Sex differences in juvenile activities, such as rough-and-tumble play, peer preferences, and infant interest, share similarities in humans and monkeys. Thus if activity preferences shape toy preferences, male and female monkeys may show toy preferences similar to those seen in boys and girls. We compared the interactions of 34 rhesus monkeys, living within a 135 monkey troop, with human wheeled toys and plush toys. Male monkeys, like boys, showed consistent and strong preferences for wheeled toys, while female monkeys, like girls, showed greater variability in preferences. Thus, the magnitude of preference for wheeled over plush toys differed significantly between males and females. The similarities to human findings demonstrate that such preferences can develop without explicit gendered socialization. We offer the hypothesis that toy preferences reflect hormonally influenced behavioral and cognitive biases which are sculpted by social processes into the sex differences seen in monkeys and humans.     

Sex of children and ultimate family size by time and class

Abstract

Data from this study and five earlier studies are analyzed to determine the magnitude and significance of the influence of sex combinations of prior children upon the ultimate (or completed) number of children in the family. In addition to confirming the observation of earlier investigators that the influence of combinations of sexes in the first two children differs by geographic area, it is shown that a difference has occurred in a single region over time, and the data for the most recent cohort suggest an effect of social class as well. Three measures of association (the corrected odds ratio, the natural logarithm of this ratio, and the fourfold point correlation) point to a small magnitude of the influence studied even when it is present at a statistically significant level. Notes on sample size relative to levels of α and β errors are included, as is discussion of a valid method of combining contingency tables.     

Age-related changes of body composition structure based on differences in morphological qualities of Japanese preschool children

This study aims to clarify age-related changes of body composition structure in terms of the percentages of body fat and muscle (muscle mass/weight×100) in preschool children by using BMI. The subjects were 533 preschool children, comprising 260 boys and 273 girls. Regression analysis for BMI was performed and a regression polynomial of a proper order was determined. After examining the validity of the order in a regression polynomial for %Fat and muscle percentages for BMI, a regression polynomial evaluation chart was made up. After judging the degree of fat or muscle accumulation from BMI and the fat or muscle percentages for each age group of the boys and girls, a frequency distribution map of excessive development and underdevelopment of fat and muscle was drawn up and its age-related changes were examined. As a result, a complementary relationship was confirmed to exist between BMI and %Fat in preschool children. In contrast, an opposite relationship was found for BMI and muscle percentages. These results suggest that BMI can be used as an index of muscle percentages as well as %Fat. As a final result, the distribution composition map of fat and muscle percentages for BMI does not show changes with age from infancy in preschool boys as a whole, but it does show such changes in girls. It is inferred that preschool girls show, due to early maturity, earlier changes (fat decrease) toward an integrated child's body than do boys.     

Effect of noise and filtering on largest Lyapunov exponent of time series associated with human walking

This study aimed to determine the effect of added noise, filtering and time series length on the largest Lyapunov exponent (LyE) value calculated for time series obtained from a passive dynamic walker. The simplest passive dynamic walker model comprising of two massless legs connected by a frictionless hinge joint at the hip was adopted to generate walking time series. The generated time series was used to construct a state space with the embedding dimension of 3 and time delay of 100 samples. The LyE was calculated as the exponential rate of divergence of neighboring trajectories of the state space using Rosenstein’s algorithm. To determine the effect of noise on LyE values, seven levels of Gaussian white noise (SNR = 55–25 dB with 5 dB steps) were added to the time series. In addition, the filtering was performed using a range of cutoff frequencies from 3 Hz to 19 Hz with 2 Hz steps. The LyE was calculated for both noise-free and noisy time series with different lengths of 6, 50, 100 and 150 strides. Results demonstrated a high percent error in the presence of noise for LyE. Therefore, these observations suggest that Rosenstein’s algorithm might not perform well in the presence of added experimental noise. Furthermore, findings indicated that at least 50 walking strides are required to calculate LyE to account for the effect of noise. Finally, observations support that a conservative filtering of the time series with a high cutoff frequency might be more appropriate prior to calculating LyE.     

The effects of walking speed on obstacle crossing in healthy young and healthy older adults

The effects of walking speed and age on the peak external moments generated about the joints of the trailing limb during stance just prior to stepping over an obstacle and on the kinematics of the trailing limb when crossing the obstacle were investigated in 10 healthy young adults (YA) and 10 healthy older adults (OA). The peak hip and knee adduction moments in OA were 21-43% greater than those in YA (p相似文献   

Sex differences in telomeres and lifespan

Males and females often age at different rates resulting in longevity 'gender gaps', where one sex outlives the other. Why the sexes have different lifespans is an age-old question, still fiercely debated today. One cellular process related to lifespan, which is known to differ according to sex, is the rate at which the protective telomere chromosome caps are lost. In humans, men have shorter lifespans and greater telomere shortening. This has led to speculation in the medical literature that sex-specific telomere shortening is one cause of sex-specific mortality. However, telomere shortening may be a cause for and/or a consequence of the processes that govern survival, and to infer general principles from single-taxon studies may be misleading. Here, we review recent work on telomeres in a variety of animal taxa, including those with reverse sexual lifespan dimorphism (i.e., where males live longer), to establish whether sex-specific survival is generally associated with sex differences in telomere dynamics. By doing this, we attempt to tease apart the potential underlying causes for sex differences in telomere lengths in humans and highlight targets for future research across all taxa.     

Sex differences in behaviour as an indirect consequence of mating system

A considerable literature has been devoted to documenting differences between the sexes. However, relatively little attention has hitherto been directed towards those differences that arise as an indirect consequence of mating system even though they can have profound implications for the daily lives of the animals involved. In this review we focus on differences in the non-reproductive behaviour of fish and relate these to sexual dimorphism in size and morphology, and to variance in fitness between the sexes. In line with our expectation, differences in distributional ecology, schooling, aggression, predator avoidance and foraging are exaggerated in sexually dimorphic species and polygamous mating systems. Nonetheless, the behaviour of males and females may also differ in sexually monomorphic and monogamous species. We conclude by highlighting promising directions for further research.     

Sex differences in spatial cognition in an invertebrate: the cuttlefish

Evidence of sex differences in spatial cognition have been reported in a wide range of vertebrate species. Several evolutionary hypotheses have been proposed to explain these differences. The one best supported is the range size hypothesis that links spatial ability to range size. Our study aimed to determine whether male cuttlefish (Sepia officinalis; cephalopod mollusc) range over a larger area than females and whether this difference is associated with a cognitive dimorphism in orientation abilities. First, we assessed the distance travelled by sexually immature and mature cuttlefish of both sexes when placed in an open field (test 1). Second, cuttlefish were trained to solve a spatial task in a T-maze, and the spatial strategy preferentially used (right/left turn or visual cues) was determined (test 2). Our results showed that sexually mature males travelled a longer distance in test 1, and were more likely to use visual cues to orient in test 2, compared with the other three groups. This paper demonstrates for the first time a cognitive dimorphism between sexes in an invertebrate. The data conform to the predictions of the range size hypothesis. Comparative studies with other invertebrate species might lead to a better understanding of the evolution of cognitive dimorphism.