Diurnal variation in stature: is stretching the answer?

Musculoskeletal Health in Active Ambulatory Men with Cerebral Palsy and the Impact of Vitamin D

Purpose: (1) To determine the contribution of diet, time spent outdoors, and habitual physical activity (PA) on vitamin D status in men with cerebral palsy (CP) compared to physical activity matched controls (TDC) without neurological impairment; (2) to determine the role of vitamin D on musculoskeletal health, morphology, and function in men with CP compared to TDC. Materials and methods: A cross-sectional comparison study where 24 active, ambulant men with CP aged 21.0 ± 1.4 years (Gross Motor Function Classification Score (I–II) and 24 healthy TDC aged 25.3 ± 3.1 years completed in vivo assessment of musculoskeletal health, including: vastus lateralis anatomical cross-sectional area (VL ACSA), isometric knee extension maximal voluntary contraction (KE iMVC), 10 m sprint, vertical jumps (VJ), and radius and tibia bone ultrasound (US) T_us and Z_us scores. Assessments of vitamin D status through venous samples of serum 25-hydroxyvitamin D (25(OH)D) and parathyroid hormone, dietary vitamin D intake from food diary, and total sun exposure via questionnaire were also taken. Results: Men with CP had 40.5% weaker KE iMVC, 23.7% smaller VL ACSA, 22.2% lower VJ, 14.6% lower KE iMVC/VL ACSA ratio, 22.4% lower KE iMVC/body mass (BM) ratio, and 25.1% lower KE iMVC/lean body mass (LBM) ratio (all p < 0.05). Radius T_us and Z_us scores were 1.75 and 1.57 standard deviations lower than TDC, respectively (p < 0.05), whereas neither tibia T_us nor Z_us scores showed any difference compared to TDC (p > 0.05). The 25(OH)D was not different between groups, and 90.9% of men with CP and 91.7% of TDC had low 25(OH)D levels when compared to current UK recommendations. The 25(OH)D was positively associated with KE iMVC/LBM ratio in men with CP (r = 0.500, p = 0.020) but not in TDC (r = 0.281, p = 0.104). Conclusion: Musculoskeletal outcomes in men with CP were lower than TDC, and despite there being no difference in levels of 25(OH)D between the groups, 25 (OH)D was associated with strength (KE iMVC/LBM) in the CP group but not TDC. The findings suggest that vitamin D deficiency can accentuate some of the condition-specific impairments to musculoskeletal outcomes.

Diurnal variation of body height in children with idiopathic scoliosis

BACKGROUND

Body height (BH) measurement is an important part of the clinical evaluation of children with idiopathic scoliosis (IS) as its progression is defined based on the observation of a growth spurt.

OBJECTIVE

The aim of the study is to assess diurnal variation of BH in children with IS.

METHODS

BH was measured in 98 children with IS (Cobb angle: 10∘-52∘, mean 21.2∘± 9.9∘) both in standing and sitting position. The measurements were performed 4 times a day - between: (1) 7:00 and 8:00; (2) 11:00 and 12:00; (3) 15:00 and 16:00 and (4) 19:00 and 20:00.

RESULTS

A significant decrease in BH during the day was observed in both standing and sitting positions (p< 0.001). The highest decrease in height was observed between the measurements performed between 7:00 and 8:00 and measurements carried out in the evening (19:00-20:00). For standing, the mean loss of height was 0.7 cm (± 0.7), i.e. 0.43% of initial standing height, for sitting the mean decrease in height was 0.7 cm (± 0.7), i.e. 0.79% of initial sitting height.

CONCLUSIONS

BH decreases in children with IS during daytime. Due to diurnal BH variation, the time of the day should be recorded when measuring patients with IS.

Discrepancies between reported and cadaveric body size measurements associated with a modern donated skeletal collection

Body mass and stature estimation methods used in biological anthropology require materials with known body size information. There are several types of body size data that can be associated with skeletal collections. However, discussion regarding the reliability and suitability of these types of information for anthropological research is scarce. This paper focuses on differences between reported and recorded cadaver weights and heights associated with a modern donated skeletal collection, similar to these commonly used in anthropological research. In addition, the study identifies factors that may influence these discrepancies. The results show statistically significant differences between reported and cadaver body size information. Generally, reported weights, statures and body mass indices (BMI) were greater compared to the cadaver information in this sample. However, potential effects on these discrepancies varied depending on sex and information type. Age was found to influence stature discrepancy in females, and donation type had an effect on the female weight discrepancy. The results also show that body size range (weight, stature and BMI) can contribute to these discrepancies. Even though the differences between reported and cadaver data may not be significant at the population level, the individual variation can cause misclassifications of individuals depending on the data used. This study encourages researchers using modern documented collections and their body size information to openly acknowledge the types of weight and stature data used and to discuss potential problems associated with them.

Shock attenuation in the human lumbar spine during walking and running

During locomotion, each step generates a shock wave that travels through the body toward the head. Without mechanisms for attenuation, repeated shocks can lead to pathology. Shock attenuation (SA) in the lower limb has been well studied, but little is known about how posture affects SA in the spine. To test the hypothesis that lumbar lordosis (LL) contributes to SA, 27 adults (14 male, 13 female) walked and ran on a treadmill. Two lightweight, tri-axial accelerometers were affixed to the skin overlying T12/L1 and L5/S1. Sagittal plane accelerations were analyzed using power spectral density analysis, and lumbar SA was assessed within the impact-related frequency range. 3D kinematics quantified dynamic and resting LL. To examine the effects of intervertebral discs on spinal SA, supine MRI scans were used to measure disc morphology. The results showed no association between LL and SA during walking, but LL correlated with SA during running (P<0.01, R²=0.30), resulting in as much as 64% reduction in shock signal power among individuals with the highest LL. Patterns of lumbar spinal motion partially explain differences in SA: larger amplitudes of LL angular displacement and slower angular displacement velocity during running were associated with greater lumbar SA (P=0.008, R²=0.41). Intervertebral discs were associated with greater SA during running (P=0.02, R²=0.22) but, after controlling for disc thickness, LL remained strongly associated with SA (P=0.001, R²=0.44). These findings support the hypothesis that LL plays an important role in attenuating impact shocks transmitted through the human spine during high-impact, dynamic activities such as running.

Predicted body weight relationships for protective ventilation - unisex proposals from pre-term through to adult

BACKGROUND

The lung-protective ventilation bundle has been shown to reduce mortality in adult acute respiratory distress syndrome (ARDS). This concept has expanded to other areas of acute adult ventilation and is recommended for pediatric ventilation. A component of lung-protective ventilation relies on a prediction of lean body weight from height. The predicted body weight (PBW) relationship employed in the ARDS Network trial is considered valid only for adults, with a dedicated formula required for each sex. No agreed PBW formula applies to smaller body sizes. This analysis investigated whether it might be practical to derive a unisex PBW formula spanning all body sizes, while retaining relevance to established adult protective ventilation practice.

METHODS

Historic population-based growth charts were adopted as a reference for lean body weight, from pre-term infant through to adult median weight. The traditional ARDSNet PBW formulae acted as the reference for prevailing protective ventilation practice. Error limits for derived PBW models were relative to these references.

RESULTS

The ARDSNet PBW formulae typically predict weights heavier than the population median, therefore no single relationship could satisfy both references. Four alternate piecewise-linear lean body-weight predictive formulae were presented for consideration, each with different balance between the objectives.

CONCLUSIONS

The 'PBWuf + MBW' model is proposed as an appropriate compromise between prevailing practice and simplification, while also better representing lean adult body-weight. This model applies the ARDSNet 'female' formula to both adult sexes, while providing a tight fit to median body weight at smaller statures down to pre-term. The 'PBWmf + MBW' model retains consistency with current practice over the adult range, while adding prediction for small statures.

Calculation of corrected body height in idiopathic scoliosis: comparison of four methods

PURPOSE

The aim of the study was to analyze four radiographic methods of calculating the loss of body height associated with scoliosis.

METHODS

Thirty patients with right thoracic idiopathic scoliosis were examined with standing postero-anterior radiographs. Cobb angles of the upper thoracic, main thoracic and lumbar curves were measured. The loss of body height due to scoliosis was measured directly on the radiographs and then calculated using the methods of Bjure, Kono, Stokes and Ylikoski, respectively. The reproducibility of calculations was tested. Detailed analysis of two patients with similar Cobb angle but different trunk height was performed.

RESULTS

The mean Cobb angle of the main thoracic curve was 46° (21°-74°). The mean loss of body height was 23 mm (11-43 mm) calculated by method of Bjure, 7 mm (-24 to 46 mm) by Kono, 20 mm (5-47 mm) by Stokes, 14 mm (3-36 mm) by Ylikoski, versus 18 mm (3-50 mm) measured directly on radiographs. The overall difference between the loss of body heights was significant (p < 0.0001), with significant differences in pairs for: Bjure versus Kono (p < 0.0001), Stokes versus Kono (p = 0.0002), Kono versus measured (p = 0.0061) and Bjure versus Ylikoski (p = 0.0386). Strong linear correlation between the methods was found (r ≥ 0.92; p < 0.0001). High reproducibility of height loss calculations was noticed. The two patients with similar Cobb angle and different trunk height revealed similar height loss calculated, while different loss measured on radiographs.

CONCLUSIONS

There existed no overall agreement between the four methods of calculation of the loss of body height associated with scoliosis. Calculations based on the Cobb angle produced inaccuracy and could be supplemented with data considering trunk size.

Forensic anthropology casework-essential methodological considerations in stature estimation

The examination of skeletal remains is a challenge to the medical examiner's/coroner's office and the forensic anthropologist conducting the investigation. One of the objectives of the medico-legal investigation is to estimate stature or height from various skeletal remains and body parts brought for examination. Various skeletal remains and body parts bear a positive and linear correlation with stature and have been successfully used for stature estimation. This concept is utilized in estimation of stature in forensic anthropology casework in mass disasters and other forensic examinations. Scientists have long been involved in standardizing the anthropological data with respect to various populations of the world. This review deals with some essential methodological issues that need to be addressed in research related to estimation of stature in forensic examinations. These issues have direct relevance in the identification of commingled or unknown remains and therefore it is essential that forensic nurses are familiar with the theories and techniques used in forensic anthropology.

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.

The impact of school-day variation in weight and height on National Child Measurement Programme body mass index-determined weight category in Year 6 children

BACKGROUND

In England, the National Child Measurement Programme (NCMP) annually measures the weight and height of Year 6 schoolchildren (age 10-11 years). While measurement protocols are defined, the time of measurement within the school day is not. This study examined the impact of school-day variation in weight and height on NCMP body mass index (BMI)-determined weight category in Year 6 children.

METHODS

Standing height and weight were measured in morning and afternoon sessions in 74 children, boys (n= 34; height: 141.16 ± 7.45 cm; weight: 36.48 ± 9.46 kg, BMI: 18.19 ± 3.98 kg/m(2) ) and girls (n= 40; height: 144.58 ± 7.66 cm; weight: 42.25 ± 11.29 kg; BMI: 19.97 ± 3.98 kg/m(2) ) aged 11 ± 0.3 years.

RESULTS

In the whole sample, height decreased (Mean =-0.51 cm, 95% CI: -0.39 to -0.64 cm, P= 0.01), weight did not change (Mdn = 36.40 to 36.35, P= 0.09) and BMI increased (Mdn = 18.04 to 18.13, P= 0.01). In girls weight increased (Mdn = 41.40 to 41.60, P= 0.01). BMI percentile increased (Mdn = 57th to 59.5th centile, P= 0.01). One girl increased in BMI category from morning to afternoon according to the clinical cut-offs (≤2nd, >91st and >98th) and three girls increased BMI category according to the population monitoring cut-offs (≤2nd, ≥85th, ≥95th).

CONCLUSIONS

School-day variation in height (and in girls alone, weight) impact upon increased BMI and BMI percentile in afternoon versus morning measurements in Year 6 children. Although not reaching statistical significance, resultant variation in categorization at the individual level may lead to unwarranted follow-up procedures being initiated. Further research with larger samples is required to further explore the impact of daily variability in height and weight upon both clinical and population monitoring BMI-determined weight status categorization in the NCMP.

Challenges of accurately measuring and using BMI and other indicators of obesity in children

BMI is an important indicator of overweight and obesity in childhood and adolescence. When measurements are taken carefully and compared with appropriate growth charts and recommended cutoffs, BMI provides an excellent indicator of overweight and obesity that is sufficient for most clinical, screening, and surveillance purposes. Accurate measurements of height and weight require that adequate attention be given to data collection and management. Choosing appropriate equipment and measurement protocols and providing regular training and standardization of data collectors are critical aspects that apply to all settings in which BMI will be measured and used. Proxy measures for directly measured BMI, such as self-reports or parental reports of height and weight, are much less preferred and should only be used with caution and cognizance of the limitations, biases, and uncertainties attending these measures. There is little evidence that other measures of body fat such as skinfolds, waist circumference, or bioelectrical impedance are sufficiently practicable or provide appreciable added information to be used in the identification of children and adolescents who are overweight or obese. Consequently, for most clinical, school, or community settings these measures are not recommended for routine practice. These alternative measures of fatness remain important for research and perhaps in some specialized screening situations that include a specific focus on risk factors for cardiovascular or diabetic disease.

Short stature: increased in children with severe learning disability

INTRODUCTION

'Health for all children' recommends that children should be screened for growth disorders at school entry with a 0.4th centile 'cut-off'. Following the diagnosis of growth hormone deficiency in four children attending local special schools, our aim was to compare the height distribution of children attending special schools with mainstream schools.

METHODS

Children at two local special schools were measured using a Leicester height measurer and values converted to standard deviation scores (SDS). Children were categorized according to whether there were known factors that could affect height. The data were compared with those collected from local mainstream schools.

RESULTS

In total, 242 children were registered at the two special schools and 192 children were measured. The mean height SDS of children in mainstream school (n = 2301) was similar to national standards at -0.09 (SD 1.02). The mean height SDS distribution of the 192 children in special schools (age range 3.2-18.4 years; median age 11.3 years) was -0.73; 95%CI -0.9 to -0.5. In those with no established diagnosis to explain altered growth (n = 120) this was -0.613; 95%CI -0.8 to -0.4. Both pre-pubertal (n = 37) and pubertal (n = 83) children were short and eight (6.7%) had a height less than the 0.4th centile.

CONCLUSIONS

Children attending special school with severe or profound learning disability were shorter than those attending mainstream school. This is still the case following the exclusion of children with a known cause for abnormal growth. This underlines the importance of each child being assessed by professionals with a refined knowledge of normal and abnormal growth.

Effect of inspiration/expiration on height measurement

BACKGROUND

Growth parameters are a powerful screening tool in pediatric care. Accuracy assumes differing importance in different clinical settings. A small error is not clinically significant when height is obtained as a screening tool during annual well child visits. However, when assessing annual growth velocity using shorter interval visits, an error of equal magnitude might influence further management decisions. AIM AND HYPOTHESIS: To explore the effect of inspiration or expiration on height measurement. Our hypothesis was that height measurements obtained in inspiration would be greater than those obtained in expiration or without specific instructions as to status of respiration (unspecified).

METHODS

Heights of 99 individuals 8 years and older were measured in inspiration, expiration and unspecified respiratory status by two pediatric endocrinologists. Patients were measured three times in each mode. The p values were adjusted by Tukey procedure for multiple comparisons among three modes.

RESULTS

Height measurement performed in inspiration, expiration or without specific instruction as to breathing (unspecified) did affect height measurement. Mean difference +/- SEM (95% CI) between height obtained in inspiration and expiration was 0.22 +/- 0.03 cm (95% CI: 0.15, 0.29); between inspiration and unspecified 0.31 +/- 0.04 cm (95% CI: 0.22, 0.40); and between expiration and unspecified 0.092 +/- 0.03 cm (95% CI: 0.03, 0.16).

CONCLUSIONS

Based on these results, we recommend multiple height measurements using uniform technique including inspiratory/expiratory status, especially when calculating 'annualized' height velocity over short intervals.

Clinical efficacy of group-based treatment for childhood obesity compared with routinely given individual counseling

OBJECTIVE

The aim of the study was to compare the efficacy of group treatment stressing a health-promoting lifestyle with routine counseling in the treatment of childhood obesity.

DESIGN AND SUBJECTS

Seventy obese children (weight for height 115-182%) aged 7-9 years were randomized either to routine counseling (two appointments for children) or to family-based group treatment (15 separate sessions for parents and children). These sessions included nutrition education, physical activity education and behavioral therapy.

OUTCOME MEASURES

Children's weights and heights were measured at baseline, after the 6-month intervention and after the 6-month follow-up. The change of weight for height based on Finnish growth charts was used as the primary, and changes in body mass index (BMI) and BMI standard deviation scores (BMI-SDS) as secondary outcome measures.

RESULTS

Children attending the group treatment lost more weight for height (6.8%) than children receiving routine counseling (1.8%) (P=0.001). The difference was significant when the data were analyzed in four groups by the cut-off limits of 0, -5 and -10% for the change in weight for height. The respective decreases in BMI were 0.8 vs 0.0 (P=0.003) and in BMI-SDS 0.3 vs 0.2 (P=0.022). The results remained similar in adjusted analyses. Both group and routine programs were feasible with a high, 87-99%, participation rate in sessions and appointments and very low, 3% or less, attrition rate from the programs. Six months after the intervention, beneficial effects were partly lost, but for changes in weight for height and BMI, the differences between the two treatment programs still were significant, and for BMI-SDS, there was a trend.

CONCLUSIONS

Family-based group treatment that stresses a health-promoting lifestyle and is given separately for parents and children, offers an effective mode of therapy to treat obese school-aged children.

Pattern of growth and adiposity from infancy to adulthood in atopic dermatitis

BACKGROUND

Impaired linear growth has been reported in children with atopic dermatitis (AD) but the pattern of growth in height and weight through childhood and adolescence has not been described.

OBJECTIVES

To define the pattern of linear growth and adiposity in AD from early childhood through to adult life.

PATIENTS AND METHODS

Growth measurements of 70 male and 40 female patients with AD followed through childhood and adolescence were studied retrospectively and compared with the 1990 U.K. normal values. Height, weight and body mass index (BMI) were converted to standard deviation scores (SDS). Regression analysis examined whether the mean trend was different from zero.

RESULTS

While dermatitis was the predominant atopic problem in all 110 patients, 92 had a history of asthma which was mild in 85 of 92. Regression analyses showed that the trends in height, weight and BMI SDS for AD patients were significantly different from zero and also different between males and females. Both sexes were short and relatively overweight from early childhood, a trend that was more pronounced in males than females. At 5 years (school entry), the 50th centile BMI of male (but not female) patients was 0.44 kg m(-2) higher than the reference population but height and weight were lower. The age at adiposity rebound in AD males and females was 0.8 year and 0.7 year later than the U.K. population (6.2 years vs. 5.4 years and 6.2 years vs. 5.3 years, respectively). AD patients attained peak height velocity later than the 1990 U.K. population (males 16.0 years vs. 13.5 years, P = 0.0002; females 13.4 years vs. 11.0 years, P = 0.008). In addition, males had greater mean gain in height during late adolescence (12.2 vs. 8.8 cm, P = 0.03) and were shorter as young adults (170.9 vs. 177.6 cm, P = 0.0005).

CONCLUSIONS

Our patients with AD were relatively overweight very early but had a later adiposity rebound, were short in childhood and had a delayed adolescent growth spurt. Serial growth measurements should be done on all children with troublesome AD and can be helpful in counselling about the growth prognosis.

Diurnal variation of height in children

BACKGROUND

Diurnal variation of height is largely ignored in the assessment of growth in children. Diurnal decrease in stature may effect the reliability of height measurement. In this study, the degree of differences in daily height measurement were evaluated.

METHODS

A total of 478 children, aged 3-15 years (mean age 9.9 +/- 2.3 years) were enrolled in the study. The height of children were measured twice in a day. The first measurements were taken between 09:00 and 10:00 h and the second measurements between 15:00 and 16:00 h.

RESULTS

Children's height measurements differences were +1.8 to -2.7 cm, and a mean of 0.47 +/- 0.05 cm decrease was determined.

CONCLUSIONS

Little differences of height measurement could be very important in evaluating the short child. When the result of height measurement is recorded, recording the time of day is offered.

Effect of diurnal variation on body composition under consideration of selected chronobiological marker systems

Diurnal variation in body composition in relation to chronobiological parameters was analyzed in 27 healthy students (22-29 years) four times over one day from 5:35 to 0:15 h. Body composition was determined by multifrequency bioimpedance analysis at fixed frequencies (1, 5, 50, 100 kHz). Resistance (R) and reactance (Xc) were measured. Total, extra and intracellular body water (TBW, ECW, ICW), lean body mass (LBM), and fat mass (FM) were derived, and blood pressure and body temperature were measured. Friedman's ANOVA with post hoc Wilcoxon matched pairs tests revealed a diurnal variability. R and Xc declined in the course of the day. Weight, TBW, ECW, ICW, LBM and ECM increased, whereas height decreased. Chronobiology did not significantly influence FM. Body composition variables displayed inverse associations to RRdiastolic. The diurnal decrease is probably influenced by food and fluid intake. the representative values for body composition should be the morning measures.

Diurnal variation in height and the reliability of height measurements using stretched and unstretched techniques in the evaluation of short-term growth

Diurnal variation in stature is one potentially significant source of error in the evaluation of short-term growth. In order to assess the pattern of diurnal variation in height during a 12-h period, the standing height of two healthy prepubertal male siblings, 7 and 11 years of age, was measured by stretched and unstretched techniques five times a day at 3-h intervals over 8 consecutive days. The major loss of height occurred during the first 3 h after rising when the mean stretched height decreased by 0.94 cm (unstretched 1.03 cm). The maximal height loss was achieved by 1500 hours when the mean stretched height had decreased by 1.44 cm (unstretched 1.41 cm) from that recorded in the morning. Over the next 6 h there was a significant (p < 0.001) increment in both stretched and unstretched heights (+0.38 and + 0.42 cm, respectively). A stretch technique did not reduce the diurnal loss. In the second study daily height was measured in the same two siblings over 365 days: (1) to compare the reliability of measurements between stretched and unstretched techniques; and (2) to assess the effect of measurement techniques on non-linear regression analysis and time series analysis used in the evaluation of short-term growth. The differences between the original measurements and the estimates of 'true height' derived from regression curves were used as a measure of accuracy. A smaller SD of these differences and a significantly smaller number of outliers (outside +/-2 SD) than expected (p < 0.05) was generated using the stretched technique (SD = 0.19 cm; 14 outliers) compared the unstretched (SD = 0.23 cm; 53 outliers). Measurement technique did not affect the height and height velocity regression curves and the results of time series analysis. In the evaluation of short-term growth we recommend that children should be measured by a standard stretch technique between 1800 and 2100 hours when the diurnal variation in height is smallest.

Assessment of nutritional status and body composition in children using physical anthropometry and bioelectrical impedance: influence of diurnal variations

BACKGROUND

To observe whether there are diurnal variations when assessing children's body composition, using physical anthropometric and bioelectrical impedance (BI) methods.

METHODS

In 32 children (18 females and 14 males) aged between 7.1 and 14.9 years, weight, height, arm circumference (AC), four skinfolds, and total body impedance (Z) were measured at 8 A.M., 12 noon, 4 P.M., and 8 P.M. on the same day. Body mass index (BMI), skinfolds sum (SS), total body water (TBW), fat-free mass (FFM), and fat mass (FM) were also calculated at these times.

RESULTS

Height at 8 P.M. was 1.156 +/- 0.54 cm less than at 8 A.M. (P < 0.001) and BMI increased 0.434 +/- 0.29 kg/m2 at 8 P.M. (P < 0.001). Weight, SS and AC underwent no significant changes in the course of the day. Z was 5.83% less at 8 P.M. than at 8 A.M. (P < 0.001), yielding a TBW and FFM increase at 8 P.M. of 0.855 +/- 1.061 and 1.173 +/- 1.47 kg, respectively (P < 0.001).

CONCLUSIONS

In children there is a diurnal decrease in height, impedance and FM, and an increase in BMI, TBW, and FFM. These factors must be taken into account when using such methods for assessing nutritional status in childhood.

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.