Evidence of saltatory growth in infancy

Expected and Desirable Preterm and Small Infant Growth Patterns

Adequate nutrition is necessary for achieving optimal growth and neurodevelopment. Growth is a natural and expected process that happens concomitantly with rapid advancements in neurodevelopment. Serial weight, length, and head circumference growth measures are essential for monitoring development, although identifying pathological deviations from normal growth can pose challenges. Appropriate growth assessments require considerations that a range of sizes for length, head circumference, and weight are expected and appropriate. Because of genetic differences and morbidities, there is a considerable overlap between the growth of healthy infants and those with growth alterations. Parents tend to be over-concerned about children who plot low on growth charts and often need reassurance. Thus, the use of terms such as "poor" growth or growth "failure" are discouraged when growth is approximately parallel to growth chart curves even if their size is smaller than specific percentiles. No specific percentile should be set as a growth goal; individual variability should be expected. An infant's size at birth is important information that goes beyond the common use of prognostic predictions of appropriate compared with small or large for gestational age. The lower the birthweight, the lower the nutrient stores and the more important the need for nutrition support. Compared to term infants, preterm infants at term-equivalent age have a higher percentage of body fat, but this diminishes over the next months. Current research findings support expert recommendations that preterm infants should grow, after early postnatal weight loss, similar to the fetus and then term-born infants, which translates to growth approximately parallel to growth chart curves. There is no need for a trade-off between optimum cognition and optimum future health. Each high-risk infant needs individualized nutrition and growth assessments. This review aims to examine infant growth expectations and messaging for parents of preterm and term-born infants within the broader causal framework.

Short-term dynamics of linear growth among Peruvian infants in the first year of life in a population with linear growth faltering

OBJECTIVES

Infant growth is recognized to vary over the short term, with periods of greater and lesser linear growth velocity. Our objectives were to (1) examine the potential differences in overall growth profiles between children who experienced cumulative growth faltering in the first year of life consistent with that seen by many children living in poverty in low- and middle-income countries, versus children without growth faltering and (2) test whether biological factors were associated with the timing of magnitude of growth saltations.

METHODS

Thrice-weekly measurements of length were recorded for n = 61 Peruvian infants (28 boys and 33 girls) enrolled from birth to 1 year. A total of 6040 measurements were analyzed. We tested for the evidence of saltatory growth and used hurdle models to test whether the timing and magnitude of saltations varied between children with greater or lesser growth faltering.

RESULTS

There were no differences in the duration of stasis periods or magnitude of growth saltations between children who were stunted at 1 year old (N = 18) versus those who were not stunted (N = 43). Children who experienced greater declines in LAZ in the first year of life trended toward longer periods between saltations than those with less of a decline (14.5 days vs. 13.4 days, p = .0512). A 1-unit increase in mid upper arm circumference for age Z-score in the 21 days prior was associated with 35% greater odds of a saltation occurring (p < .001), and a 0.128 cm greater saltation (p < .001).

CONCLUSIONS

After characterizing infant growth into periods of saltation and stasis, our results suggest that increases in weight preceded increases in length.

Learning to Move in a Changing Body in a Changing World

Infants of all species learn to move in the midst of tremendous variability and rapid developmental change. Traditionally, researchers consider variability to be a problem for development and skill acquisition. Here, we argue for a reconsideration of variability in early life, taking a developmental, ecological, systems approach. Using the development of walking in human infants as an example, we argue that the rich, variable experiences of infancy form the foundation for flexible, adaptive behavior in adulthood. From their first steps, infants must cope with changes in their bodies, skills, and environments. Rapid growth spurts and a continually expanding environment of surfaces, elevations, and obstacles alter the biomechanical constraints on balance and locomotion from day to day and moment to moment. Moreover, infants spontaneously generate a variable practice regimen for learning to walk. Self-initiated locomotion during everyday activity consists of immense amounts of variable, time-distributed, error-filled practice. From infants' first steps and continuing unabated over the next year, infants walk in short bursts of activity (not continual steps), follow curved (not straight) paths, and take steps in every direction (not only forward)-all the while, accompanied by frequent falls as infants push their limits (rather than a steady decrease in errors) and explore their environments. Thus, development ensures tremendous variability-some imposed by physical growth, caregivers, and a changing environment outside infants' control, and some self-generated by infants' spontaneous behavior. The end result of such massive variability is a perceptual-motor system adept at change. Thus, infants do not learn fixed facts about their bodies or environments or their level of walking skill. Instead, they learn how to learn-how to gauge possibilities for action, modify ongoing movements, and generate new movements on the fly from step to step. Simply put, variability in early development is a feature, not a bug. It provides a natural training regimen for successfully navigating complex, ever-changing environments throughout the lifespan. Moreover, observations of infants' natural behavior in natural, cluttered environments-rather than eliciting adult-like behaviors under artificial, controlled conditions-yield very different pictures of what infants of any species do and learn. Over-reliance on traditional tasks that artificially constrain variability therefore risks distorting researchers' understanding of the origins of adaptive behavior.

Evaluation of the Healthy Eating Index-Toddlers-2020

BACKGROUND

With the addition of new guidance for children from birth to 24 months in the Dietary Guidelines for Americans, 2020-2025 (DGA), a Healthy Eating Index (HEI) was developed for toddlers.

OBJECTIVE

To evaluate the psychometric properties of the HEI-Toddlers-2020, 5 analyses relevant to construct and concurrent validity and 2 related to reliability were examined.

DESIGN

Twenty-four-hour diet recall data from the cross-sectional National Health and Nutrition Examination Survey (2011-2018) were used. In addition, exemplary menus were analyzed.

PARTICIPANTS/SETTING

The main analytic sample included toddlers aged 12 through 23 months (n = 838), with additional analyses of toddlers aged 12 through 35 months (n = 1,717) from the United States. Included participants had valid diet recalls and available weight-for-age data.

MAIN OUTCOME MEASURES

Outcomes measures included HEI-Toddlers-2020 total and component scores on menus, population distributions, and correlations.

STATISTICAL ANALYSES

HEI total and component scores were calculated using menus from the American Academy of Pediatrics and Healthy Eating Research. Score means and distributions were estimated using a Markov Chain Monte Carlo approach with National Health and Nutrition Examination Survey data (2011-2018). Principal component analysis explored dimensions and Pearson correlations examined components, energy, and Cronbach α. In addition, HEI-Toddlers-2020 and HEI-2020 scores were compared for identical intakes at age 24 months.

RESULTS

For validity, exemplary menus received high scores with the HEI-Toddlers-2020. The mean ± SE total HEI-Toddlers-2020 score for toddlers aged 12 through 23 months was 62.9 ± 0.78 and ranged from 40.1 to 84.4 (1st to 99th percentile). Correlation between diet quality and diet quantity was low (-0.15); the scree plot revealed multiple factors. In addition, total scores for identical intakes were approximately 1.5 points higher for HEI-Toddlers-2020 compared with HEI-2020 (difference range for component scores, -4.97 to 4.89). For reliability, most of the intercorrelations among components were low to moderate (0 to 0.49), with a few exceptions among related components. Cronbach α was .48. These results indicate that the index is multidimensional, with no single component driving the total score, and no unnecessary components that are highly correlated with another component.

CONCLUSIONS

The results demonstrated evidence supportive of validity and reliability. The HEI-Toddlers-2020 can be used to assess alignment with the DGA for toddlers.

Aflatoxin exposure and child nutrition: measuring anthropometric and long-bone growth over time in Nepal

BACKGROUND

Naturally occurring aflatoxins may contribute to poor growth and nutritional statuses in children.

OBJECTIVES

We analyzed the relationship between contemporary and lagged aflatoxin exposure and 1) length-for-age z-score (LAZ); and 2) length, knee-heel length, stunting, weight-for-age z-score (WAZ), and weight-for-length z-score (WLZ).

METHODS

We conducted a longitudinal birth cohort study involving 1675 mother-infant dyads in rural Nepal. Participants were repeatedly visited from pregnancy to 2 years of age (2015-2019). One blood sample was collected during pregnancy and 4 samples were collected from the children at 3, 6, 12, and 18-22 months of age to measure concentrations of aflatoxin B1 (AFB1)-lysine adduct. Multivariate linear fixed-effects and logistic models with generalized estimating equations were used to identify associations between child growth and aflatoxin exposure.

RESULTS

AFB1-lysine adducts were detected in the majority of children (at 3 months, 80.5%; at 6 months, 75.3%; at 12 months, 81.1%; and at 18-22 months, 85.1%) and in 94.3% of pregnant women. Changes in contemporary ln child AFB1-lysine adduct concentrations were significantly associated with changes in LAZ (β, -0.05; 95% CI, -0.09 to -0.02; P = 0.003), length (β, -0.19; 95% CI, -0.29 to -0.10; P < 0.001), knee-heel length (β, -0.09; 95% CI, -0.13 to -0.05; P < 0.001), and WAZ (β, -0.04; 95% CI, -0.07 to -0.005; P = 0.022). Serum aflatoxin concentrations were associated with stunting (OR, 1.18; 95% CI, 1.05-1.32; P = 0.005). Similar results were found in the models using changes in contemporary ln AFB1 adjusted for changes in child weight, with significant associations with changes in WLZ (β, -0.07; 95% CI, -0.10 to -0.03; P < 0.001). Changes in time-lagged ln AFB1 (unadjusted and adjusted for changes in child weight) were associated with changes in length and knee-heel length.

CONCLUSIONS

Our results add to the growing body of evidence confirming chronic aflatoxin exposure and suggest that exposure is significantly correlated with various negative growth outcomes, which may vary by child weight status. This trial was registered at clinicaltrials.gov as NCT03312049.

An Ecological Approach To Learning In (Not And) Development

The ecological approach is a framework for studying the behavior of animals in their environments. My version of an ecological approach focuses on learning in the context of development. I argue that the most important thing animals learn is behavioral flexibility. They must acquire the ability to flexibly guide their behavior from moment to moment in the midst of developmental changes in their bodies, brains, skills, and environments. They must select, modify, and create behaviors appropriate to the current situation. In essence, animals must learn how to learn. I describe the central concepts and empirical strategies for studying learning in development and use examples of infants coping with novel tasks to give a flavor of what researchers know and still must discover about the functions and processes of learning (to learn) in (not and) development.

Motor Development: Embodied, Embedded, Enculturated, and Enabling

Motor development and psychological development are fundamentally related, but researchers typically consider them separately. In this review, we present four key features of infant motor development and show that motor skill acquisition both requires and reflects basic psychological functions. ( a) Motor development is embodied: Opportunities for action depend on the current status of the body. ( b) Motor development is embedded: Variations in the environment create and constrain possibilities for action. ( c) Motor development is enculturated: Social and cultural influences shape motor behaviors. ( d) Motor development is enabling: New motor skills create new opportunities for exploration and learning that instigate cascades of development across diverse psychological domains. For each of these key features, we show that changes in infants' bodies, environments, and experiences entail behavioral flexibility and are thus essential to psychology. Moreover, we suggest that motor development is an ideal model system for the study of psychological development.

Development (of Walking): 15 Suggestions

Although a fundamental goal of developmental science is to identify general processes of change, developmental scientists rarely generalize beyond their specific content domains. As a first step toward a more unified approach to development, we offer 15 suggestions gleaned from a century of research on infant walking. These suggestions collectively address the multi-leveled nature of change processes, cascades of real-time and developmental events, the diversity of developmental trajectories, inter- and intraindividual variability, starting and ending points of development, the natural input for learning, and the roles of body, environment, and sociocultural context. We argue that these 15 suggestions are not limited to motor development, and we encourage researchers to consider them within their own areas of research.

Development of an evidence-based clinical practice guideline on linear growth measurement of children

Growth is an important indicator of child health; however, measurements are frequently inaccurate and unreliable. This article reviews the literature on linear growth measurement error and describes methods used to develop and evaluate an evidence-based clinical practice guideline on the measurement of recumbent length and stature of infants, children, and adolescents. Systematic methods were used to identify evidence to answer clinical questions about growth measurement. A multidisciplinary team critically appraised and synthesized the evidence to develop clinical practice recommendations using an evidence-based practice rating scheme. The guideline was prospectively evaluated through internal and external reviews and a pilot study to ensure its validity and reliability. Adoption of the clinical practice guideline can improve the accuracy and reliability of growth measurement data.

Infant head circumference growth is saltatory and coupled to length growth

BACKGROUND

Rapid growth rates of head circumference and body size during infancy have been reported to predict developmental pathologies that emerge during childhood.

AIMS

This study investigated whether growth in head circumference was concordant with growth in body length.

SUBJECTS

Forty infants (16 males) were followed between the ages of 2 days and 21 months for durations ranging from 4 to 21 months (2616 measurements).

STUDY DESIGN

Longitudinal anthropometric measurements were assessed weekly (n=12), semi-weekly (n=24) and daily (n=4) during home visits. Individual head circumference growth was investigated for the presence of saltatory patterns. Coincident analysis tested the null hypothesis that head growth was randomly coupled to length growth.

RESULTS

Head circumference growth during infancy is saltatory (p<0.05), characterized by median increments of 0.20 cm (95% confidence interval, 0.10-0.30 cm) in 24-h, separated by intervals of no growth ranging from 1 to 21 days. Daily assessments identified that head growth saltations were coupled to length growth saltations within a median time frame of 2 days (interquartile 0-4, range 1-8 days). Assessed at semi-weekly and weekly intervals, an average 82% (SD 0.13) of head growth saltations was non-randomly concordant with length growth (p≤0.006).

CONCLUSIONS

Normal infant head circumference grows by intermittent, episodic saltations that are temporally coupled to growth in total body length by a process of integrated physiology that remains to be described.

Short-term growth in head circumference and its relationship with supine length in healthy infants

BACKGROUND

Daily changes in height have been found to be a non-linear process. Its exact pattern is still controversial. In previous studies on 34 healthy children aged 0.32-12.99 years, we found that growth is a tri-phasic process: stasis, steep changes (or saltation) and continuous growth. There is very little information in the literature about daily changes in head circumference.

AIM

The present study analysed growth in head circumference and supine length in eight healthy infants.

SUBJECT AND METHODS

Supine length and head circumference was measured five times a week during 151 days. Mean intra-observer technical error of measurement (TEM) for head circumference and supine length were 0.10 and 0.15 cm, respectively; smoothing techniques used were based on the TEM with a hard rejection criterion.

RESULTS

The three types of events previously found in supine length are also present in head circumference. The number of steep changes was greater in supine length than in head circumference.

CONCLUSION

Growth is a discontinuous and irregular process, present not only in long bones but also in skull bones. Although long-term growth curves of head circumference and supine length are different, when measured on a daily basis findings suggest that skull and long bones have a common pattern; the physiological basis needs future research.

Short-term growth at adolescence in healthy girls

In the last decade, most investigators found that growth measured on a daily or weekly basis is a non-linear process, but its precise pattern has not yet been fully determined. Data are particularly scarce during puberty. On this basis we evaluated the daily growth in 10 healthy girls during their adolescent growth spurt with replicated height measurements over a period of 128-150 days. The technical error of measurement in each girl varied between 0.08 and 0.12 cm. A jump-preserving smoothing technique based on the technical error with a hard rejection criterion was used. Growth was defined as any increment between two consecutive smoothed values greater than 6 times the standard deviation of the difference of two consecutive smoothed values under the non-growth (stasis) assumption. Steep changes in height were conventionally defined as any 1-day increment greater than 0.3 cm.

RESULTS

All girls showed stasis periods, steep changes and days with a continuous growth with a wide range of daily increments in height. The number of stasis periods in each girl varied between three and seven, lasting between 7 and 22 consecutive days. The number of steep changes in each girl ranged between one and four with a mean amplitude between 0.37 and 0.52 cm. The sum of these steep changes calculated in each girl as a percentage of total growth during the study period ranged from 15.3 to 42.9%; the remaining growth was due to continuous growth. Rhythms or cycles were not found.

CONCLUSION

Short-term growth during the pubertal growth spurt in these healthy girls is an irregular and discontinuous process, composed of three types of events: stasis, steep changes and continuous growth periods with a wide individual range of daily height increments.

Growth, body composition and hormonal axes in children and adolescents

Growth and physical maturation are dynamic processes that encompass a broad range of cellular and somatic changes. Most investigators who study growth have focused on linear growth (change in height over time), but alterations in the relative body proportions, body composition, and the regional distribution of body fat (upper body vs lower body, axial vs appendicular, and sc vs deep visceral) are essential elements for growth and sexual maturation. In fact, cardiovascular risk assessment in the adult relies heavily on the regional distribution of body fat. The antecedents for the adult pattern of fat are clearly present in the adolescent, if not the younger child. Standards for each of these parameters have been developed for multiple ethnic and racial populations and aid materially in the identification of children with normal growth and physical development, variations within the broad normal (physiological) range, and those with clearly pathological growth patterns.

The use of regularity as estimated by approximate entropy to distinguish saltatory growth

A nonlinear dynamics metric, approximate entropy (ApEn), is investigated as a diagnostic method for distinguishing between mathematical models, and the underlying mechanistic hypotheses that purport to describe the same time series experimental observations. ApEn measures the occurrence of pattern regularity within a time series, and is used here to investigate growth patterns in daily length growth. The notion investigated is that ApEn distributions for competing time series patterns expressed as mathematical formulations can be modelled by Monte Carlo and bootstrap methods and compared to the ApEn values for an original experimental data series. If the ApEn values for the different models do not overlap, then it is expected that ApEn can be utilized to distinguish these models and hypotheses, and to provide statistical assessment for the underlying biological patterns in experimental data. The conclusion is that the ApEn metric is successful as a time series diagnostic tool. It is a model-independent statistic that clearly differentiates saltatory growth from slowly varying continuous models of growth and serves to further document the saltatory nature of growth. This is a unique application of approximate entropy, illustrating the broad applicability of ApEn to biological time series, with the specific example of discriminating a saltatory growth process in longitudinal growth data. Future investigations of regularity in longitudinal time series in human biology with ApEn statistics are suggested.

Child factor in measurement dependability

A primary consideration in longitudinal growth studies is the identification of growth from error components. While previous research has considered matters of measurement accuracy and reproducibility in detail, few reports have investigated the errors of measurement due to aspects of the physiology and cooperation of the child. The present study directly assesses this source of measurement undependability for the first time. Investigation of total measurement error variance in 925 recumbent length replicates taken over stasis intervals in growth identifies that between 60% and 70% of total measurement unreliability is due to a child factor undependability. Individual differences are significant and longitudinal growth analyses should consider two to three times the technical error of measurement statistic as a reasonable estimate of the total unreliability for any single measurement of an infant's recumbent length. These results raise issues regarding analytic methods as applied to serial growth data.

Mixed distribution analysis identifies saltation and stasis growth

A maximum likelihood method of mixed distribution analysis is investigated for its utility as a method for the identification of saltation and stasis in longitudinal growth data. Daily infant growth data that have been previously identified to follow a saltatory growth process are employed. This is a novel application of the finite mixed distribution analysis (MDA), a method designed to objectively identify the presence of one or more Gaussian populations. The null hypothesis is that a single Gaussian distribution best describes the incremental growth data. This would be compatible with smooth, slowly varying daily growth patterns. This study explores whether or not two distinctive populations are evident in incremental saltatory growth data, as postulated by the saltation and stasis observations. The analysis is important in providing a growth model-independent test for the presence of saltation and stasis by a separate statistical assessment with none of the saltatory algorithm assumptions. The finite mixed distribution analysis identifies that each individual's incremental growth data is statistically best described as a mixture consisting of two components, or two populations of increments (chi-square, p < 0.05). For each individual, one of these populations is centred about a zero increment, and is compatible with the previous evidence of stasis intervals. The second population of data points is characterized by unique distributions for each individual, compatible with the previous observation that infants grow by unique patterns of growth saltations in both amplitude and frequency. The percentage of data points that fall within each of the two unique finite mixture distributions (FMDs) is similar to the proportions of discrete saltation and stasis intervals previously identified by the saltation and stasis method. Thus, the FMD analysis lends support to the nature of growth as a saltatory process characterized by two states in the daily growth of these infants. By contrast with the saltatory algorithm, which is applied to the original serial growth measurements, the mixed distribution analysis employs increments removed from their time relationships. The lack of time series sequence information precludes the mixed distribution method from reconstructing specific temporal patterns of saltatory growth. The present analysis reiterates that individual growth patterns are statistically unique and cannot be reconstructed or identified from group data.

A prospective longitudinal study of urinary excretion of a bone resorption marker in adolescents

In growing subjects, the rates of bone resorption and bone deposition are substantially larger than in non-growing individuals. The purpose of this study was to measure the urinary excretion of a specific bone resorption marker in function of adolescent growth stages in a prospective longitudinal study. A cohort of 60 adolescents (28 male and 32 female) was followed for 3.4 years (range 1.7-4.6 years). Monthly measurements of height, weight and urinary excretion of a bone resorption marker, collagen type I N-telopeptides (NTx), were made. Changes in standing height were used to classify the adolescents into one or more of six adolescent growth stages: pre-pubertal growth (continuous moderate growth rate), ascending growth spurt (increasing growth rate), peak growth spurt (growth rate higher than 7 cm/year for at least 6 months), descending growth spurt (continuous decrease in growth rate), end of growth (growth rate between 0 and 2 cm/year), and no growth. An increase in NTx excretion from the pre-pubertal to peak growth spurt of about 33% was found (44% and 27% for females and males respectively). The decreasing growth rate after the pubertal growth spurt coincided with a clear decrease in NTx excretion. These differences were statistically significant, except between the prepubertal and ascending growth stage. Individual mean NTx excretion during each growth stage was correlated with the individual's growth rate during that time (r = 0.81). There was large inter-and intra individual variability. In non-growing adolescents (growth rate 0 cm/y) NTx excretion levels were 4-7 times greater than in adults. In all females, menarche was followed by a decrease in NTx excretion. In conclusion, the excretion of a specific bone resorption marker, NTx, was correlated with the changes in growth rate during adolescence, both for males and females. There were large inter and intra-individual differences in NTx excretion during the different growth stages. In adolescents who reached their adult height at the end of the pubertal growth spurt. bone resorption decreased dramatically but remained 4-7 fold higher than in adults.

Evaluation of broiler growth velocity and acceleration in relation to pulmonary hypertension syndrome

An evaluation was made of the relationship between individual daily growth patterns and susceptibility of broiler chickens to pulmonary hypertension syndrome (PHS). In the first experiment, 46 male broilers were weighed for each of 50 d, during which time 13 developed PHS. Three temporal phases (0 to 15, 16 to 35, and 36 to 50 d) of broiler growth velocity and acceleration were examined. Correlation dimensions and Lyapunov exponents suggested evidence of chaos in growth velocity and acceleration, but the absence of detectable differences between broilers in the normal and PHS categories led us to reject the hypotheses that growth is more chaotic in normal broilers than in broilers susceptible to PHS. Growth velocity and acceleration values for mean and SD were statistically evaluated as response variables for each growth phase. Mean values for velocity during the third phase were different between broilers in the normal and PHS categories (velocity: 68.8 vs 48.9 g/d, P = 0.03, respectively) and (acceleration: 0.3 vs -1.4 g/d2, P = 0.07, respectively). The third phase SD (reflecting oscillation for velocity and acceleration) was greater for normal than for PHS birds (velocity: 26.1 vs 21.3 g/d, P = 0.13, respectively; acceleration: 39.7 vs 28.2 g/d2, P = 0.03, respectively). The hypothesis was accepted that normal birds have greater oscillations in growth velocity and acceleration than birds susceptible to PHS. A general regression neural network (GRNN) with genetic adaptive calibration was trained to predict PHS based on individual growth phases and their combinations. Data representing the first, first two, and all three phases of growth were determined to have potential for computerized diagnostic weighing. With the GRNN, birds in all three data sets were successfully classified (100%) with or without PHS. A third hypothesis, therefore, was accepted that artificial neural networks could be used to distinguish the difference between normal broilers and those susceptible to PHS. In the second experiment, only one bird was diagnosed with PHS. Velocity and acceleration neural networks from Phase 1 and Phases 1 and 2 in the first experiment were applied to the growth velocity and acceleration data of Experiment 2. The Phase 1 neural networks were the most promising in that they correctly identified 71.6 and 72.4% of the birds as normal for velocity and acceleration data, respectively. In general, data in the second experiment exceeded the neural network range of training for both velocity and acceleration, which reflected increased oscillation during the second phase of growth.

Anthropometric measurement error and the assessment of nutritional status

Anthropometry involves the external measurement of morphological traits of human beings. It has a widespread and important place in nutritional assessment, and while the literature on anthropometric measurement and its interpretation is enormous, the extent to which measurement error can influence both measurement and interpretation of nutritional status is little considered. In this article, different types of anthropometric measurement error are reviewed, ways of estimating measurement error are critically evaluated, guidelines for acceptable error presented, and ways in which measures of error can be used to improve the interpretation of anthropometric nutritional status discussed. Possible errors are of two sorts; those that are associated with: (1) repeated measures giving the same value (unreliability, imprecision, undependability); and (2) measurements departing from true values (inaccuracy, bias). Imprecision is due largely to observer error, and is the most commonly used measure of anthropometric measurement error. This can be estimated by carrying out repeated anthropometric measures on the same subjects and calculating one or more of the following: technical error of measurement (TEM); percentage TEM, coefficient of reliability (R), and intraclass correlation coefficient. The first three of these measures are mathematically interrelated. Targets for training in anthropometry are at present far from perfect, and further work is needed in developing appropriate protocols for nutritional anthropometry training. Acceptable levels of measurement error are difficult to ascertain because TEM is age dependent, and the value is also related to the anthropometric characteristics of the group of population under investigation. R > 0.95 should be sought where possible, and reference values of maximum acceptable TEM at set levels of R using published data from the combined National Health and Nutrition Examination Surveys I and II (Frisancho, 1990) are given. There is a clear hierarchy in the precision of different nutritional anthropometric measures, with weight and height being most precise. Waist and hip circumference show strong between-observer differences, and should, where possible, be carried out by one observer. Skinfolds can be associated with such large measurement error that interpretation is problematic. Ways are described in which measurement error can be used to assess the probability that differences in anthropometric measures across time within individuals are due to factors other than imprecision. Anthropometry is an important tool for nutritional assessment, and the techniques reported here should allow increased precision of measurement, and improved interpretation of anthropometric data.

The timing hypothesis and body proportionality of the intra-uterine growth retarded infant

Intra-uterine growth retardation (IUGR) is a heterogeneous designation, as seen in the fact that neonatal morbidity and mortality differ for IUGR infants that are disproportionate vs proportionate based on the ponderal index (weight/height(3)). Much less is known, however, concerning the etiology of these two forms. This study tests the hypothesis that the form of IUGR (proportionate vs disproportionate) is related to the timing of stress during gestation, specifically, that linear growth is compromised by second trimester stress and the ponderal index is compromised by third trimester stress. This hypothesis is tested using data on 755 full-term mother-infant pairs studied prospectively in rural northern Malawi where the seasonal stress of the pre-harvest rainy season (PHRS) is a regular occurrence. The results indicate that exposure to PHRS in the second trimester is not associated with weight, length, or the ponderal index at birth. Exposure to PHRS in the third trimester is associated with diminished birth weight and length, but not ponderal index. The results do not support the timing hypothesis, at least as previously framed in the literature, and suggest the possibility that linear growth may precede or be more sensitive to prenatal stress than the ponderal index. Am. J. Hum. Biol. 11:638-646, 1999. Copyright 1999 Wiley-Liss, Inc.

The timing of maternal weight gain during pregnancy and fetal growth

The morbidity, mortality, and growth patterns of intrauterine growth retarded (IUGR) infants vary according to body proportionality, or the ponderal index. Much less in known, however, about the factors that give rise to the various forms of IUGR. This study tests that hypothesis that the rate of maternal weight gain during early/mid and late pregnancy are differentially related to body size and proportions at birth in a nutritionally stressed population in rural Malawi. The data consist of prospectively collected measurements of maternal weight and infant size at birth on 272 mother-infant pairs. The results reveal that early/mid and late weight gain are both related to birth weight and length, but not to the ponderal index. Late weight gain is particularly predictive of infant size among thin women (BMI </= 18.5) and is several times stronger than early/mid weight gain. These findings do not support the timing hypothesis as previously stated in the literature, but do add to the suggestions arising from a disparate literature that growth acceleration in length may precede acceleration in weight-for-length during a period of nutritional replection in phases of the life cycle characterized by rapid growth. Am. J. Hum. Biol. 11:627-637, 1999. Copyright 1999 Wiley-Liss, Inc.

Micro and macro perspectives in auxology: findings and considerations upon the variability of short term and individual growth and the stability of population derived parameters

The present paper links the two most contrasting aspects of auxology, and addresses the apparent discrepancy between the variability and pulsatility of short term individual growth, and the stability of population derived parameters. When body stature is measured at monthly intervals, an irregular incremental pattern becomes obvious, with a number of large scale components such as series of prepubertal and pubertal growth spurts, seasonal influences on height gain, and influences of the psychosocial and economic background. When measurement intervals decrease, the patterns of stature increment appear even more irregular, and a number of short scale components become apparent, that are distinct from measurement error. Observations are presented that suggest growth being a pulsatile, a periodic, a saltatory, respectively a chaotic event as suggested by some recent studies in animals and in human newborns. Accurate measurements of the lower leg at intervals of 24 hours support the idea of short term growth being characterized by chaotic series of 'mini growth spurts' that occur at intervals of approximately 4-9 days. The amplitude of mini growth spurts ranges between 2 and some 10 mm, and also growth velocity of each spurt varies considerably so that one spurt needs between less than one and up to several days for completion. The very opposite of the variability of individual growth was found in populations. A meta-analysis of 40 male and 51 female European and US American growth studies revealed an almost uniform general pattern of average stature increment during the last 100 years. An additional analysis of stature variation of very large Japanese and Czechoslovakian growth surveys, with all together more than 23000000 measurements, and more than 500000 German preschool and school measurements, suggested similar uniformity in the standard deviation of stature.

An example of variation and pattern in saltation and stasis growth dynamics

The serial data from two siblings, aged 6.6 and 7.5 years of age at the initiation of the study, measured each evening for total standing height during 365 days, are analysed by two methods to investigate the nature of the underlying growth pattern. The saltation and stasis model, designed to identify the presence of statistically significant pulses in sequential data, is compared for goodness-of-fit to first to sixth degree polynomial functions, used to investigate the presence of a slowly varying smooth continuous function in the data, and high order polynomials of the same degree of flexibility as the individual's saltation and stasis results. The saltation and stasis model is found to better-fit the experimental data than the slowly varying smooth continuous functions (p < 0.01 to 0.001). The timing characteristics of the saltation and stasis patterns are investigated and the temporal patterns are suggestive of a non-random, aperiodical deterministic system.

Wrinkles induced by the use of smoothing procedures applied to serial growth data

This paper elucidates the effects of moving average filters when applied to serial growth measurements. This is a question of interest because smoothing procedures are inherently part of a number of analytical methods presently employed in auxological analyses. Particular attention is paid to sequential growth data analysed to identify what has been described as pulsatile, saltation and stasis patterns or mini-growth spurts. When applied to pulsatile, or saltatory, time series data the process of smoothing itself creates artifactual temporal patterns in the time series data similar to previously described mini growth spurts while removing the actual pulsatile characteristics of the data. These observations illustrate that smoothing approaches add noise to time series data while removing meaningful patterns in the original data sequence. Analyses employing such approaches produce results that include waveforms or other fluctuations compatible with an underlying pulsatile driving mechanism, but do not necessarily reflect the temporal characteristics of the original biological process.

Short-term growth: evidence for chaotic series of mini growth spurts in rat growth

Five thousand and eighteen quadruplet daily measurements of lower-leg length of 62 female and 81 male rats, were performed in order to characterize short-term growth. Within a short time, growth proceeds irregularly and consists of multiple incremental bursts (mini growth spurts) with no evidence for strict periodic behavior. Mini growth spurts are S-shaped incremental patterns that can be characterized by double-exponential functions (Gompertz's functions). Gompertz's functions are S-shaped, and can be defined by three parameters that identify amplitude, inflection point (age at peak growth velocity), and slope. The latter not only refers to the rapidity of each incremental burst, but also alludes to the duration that one incremental burst needs for completion. In regard to these characteristics, mini growth spurts differ significantly between the sexes in rats. Mean amplitude of mini growth spurts was 2153 microm (SD 1034 microm) in female rats and 2958 microm (SD 1614 microm) in male rats. Peak growth velocity of mini growth spurts appeared lower in male rats than in female rats. Female rats showed mean gamma of -1.23 (SD 0.72), whereas male rats showed mean y of -0.96 (SD 0.72). Partial growth hormone deficiency led to a modification in rats that was reversed when exogenous growth hormone was administered. Mean intervals between subsequent mini growth spurts ranged between 4.2 and 4.6 days, but the large variation of these intervals (SD between 1.6 and 2.3 days) and the fact that neither spurt-spurt interval nor spurt amplitude appeared predictable, strongly suggest chaotic behavior of mini growth spurts.

A brief history of the study of human growth dynamics

Human growth is non-linear and short term changes in height velocity cannot be used to predict future growth. This paper discusses the current knowledge of growth dynamics in the context of a historical review of the subject.