By Tom Green
Growth and physical maturation are dynamic processes that encompass a broad spectrum of cellular and somatic changes . Growth refers to measurable changes in body composition and various systems within the body, whereas biological maturation refers to significant changes to a number of physiological and structural processes . These processes present large inter-individual variation in magnitude, timing and tempo in youth, creating complex and extensive differences in the programming needs of athletes . The transition from childhood to adulthood is known as adolescence and marks the fastest period of growth known as peak height velocity (PHV). However, few studies have acknowledged peak weight velocity (PWV) to the same degree, which marks the maximum rate of increase in weight during the adolescent growth spurt.
Keywords: growth, maturation, biological maturity, child, peak height velocity, mass
Studies of the body size, dimensions, and proportions of athletes have received a lot of attention for many years . This information is beneficial for sports scientists and coaches alike, who have recently seen a rise in positions that are created solely for youth athletes . Although height in athletes has not appreciably changed on average from the 1970s through to the 2000s, body mass has continued to increase .
Recent research has suggested that an advanced understanding and appreciation of training, coupled with improved access to nutritional information and/or calorie intake support this . Regardless of existing and current research, it is important that youth practitioners are not only aware of what peak weight velocity is, but perhaps more importantly, how to programme safely for athletes during accelerated periods of growth .
- Youth – The period between childhood and adulthood.
- Growth – Changes in body size, shape and composition.
- Weight – A composite of all bodily tissues, including fat free mass (FFM) and fat mass (FM)
What is the Peak Weight Velocity?
Peak weight velocity represents the greatest rate of change in body mass. After peak height velocity, there exists a time delay (12-14 months, approximately) where there is an increase in body mass compared to stature , and it is this period of time which is referred to as peak weight velocity. Growth during childhood is a relatively stable process until about the age of four, where girls grow slightly faster than boys . This balances out over time as both genders grow at an average rate of 5 to 6cm/year and 2.5kg/year until the onset of puberty .
Puberty is also a time of significant weight gain, where 50% of adult body weight is gained during adolescence. In males, peak weight velocity occurs at about the same time as peak height velocity (>14) and averages 9kg/year . In females, peak weight velocity lags behind peak height velocity by approximately 6 months and reaches 8.3kg/year at about 12.5 (age). Figure 1 provides a visual example of the weight velocity in rural Indian boys . It is important to understand that these data may differ significantly from data collected from children in more developed countries (e.g. UK and Australia) where food access is less restricted and better nutritional education is provided.
Body fat patterning is significantly different between males and females during peak weight velocity, with females demonstrating greater trunk skinfold thickness to their male counterpart, whom demonstrate larger arm and shoulder girth measures . The rate of weight gain for both males and females decelerates during the latter stages of pubertal development (Figure 1) and ends with males’ free fat mass being 25-30% greater than females, with about half of the overall body fat .
What causes Peak Weight Velocity?
Growth is determined by hormones, nutrition and hereditary factors from the athlete’s parents with environmental factors, such as: cultural background, socioeconomic status, and physical activity thought to contribute . Peak weight velocity begins with the reactivation of the hypothalamus-pituitary-gonadal (HPG) axis, which stimulates gonadotrophin-releasing hormones (GnRH) during sleep .
This elevated bioavailability of circulating hormones and androgens (testosterone, thyroxine, leptin, parathyroid hormone and growth hormone)  develop rapid changes in long bone growth relative to muscular lengthening that may disrupt structure, neuromuscular function and physical performance . Whilst excessive weight gain during childhood is linked to several health issues such as obesity, asthma and early onset arthritis , peak weight velocity may be considered the ‘normal’ alteration in mass that marks the transition between child and adulthood.
Why is Peak Weight Velocity important for athletic performance?
Physical performance is commonly measured as the outcome of motor task requiring speed, agility, strength and power [3, 9]. However, the rapid increases in body dimensions and muscle hypertrophy during adolescence suggest that movement proficiency may be affected as athletes negotiate with fluctuating levels of co-ordination (i.e. the sudden increase in body size is likely to affect co-ordination) .
As a result of the physical changes that accompany adolescence, both males and females may struggle to perform simple motor task such as balancing, running and change of direction task . Coaches must be mindful of this and allow athletes to develop new strategies and solutions in essentially a ‘new’ body .
In the absence of muscle hypertrophy, high force activities such as landing, change of direction task or heavy strength training could predispose children to poor force-attenuating capabilities, limit physical performance, and increase the relative risk of injury . However, alterations in bone mineral content, muscle size and tendon strength will occur as a result of peak weight velocity, which inevitably lead to an increase in muscle strength, power, reactive strength index and stretch shortening cycle function over time .
Like peak height velocity, exercise programmes must be monitored and supervised by a qualified practitioner during peak weight velocity to ensure that health and safety is maintained. This is more important with a vulnerable population, where the coach, scientist, or teacher has a legal, ethical, and moral responsibility for maintaining and promoting well-being .
How to measure Peak Weight Velocity?
Monitoring peak weight velocity is an active intervention that should be conducted approximately every six months to ensure that this phase is not missed . This can be achieved by plotting the athlete’s mass on a simple excel template over time, or dividing mass by time (e.g. kilograms per year [kg/yr]) to produce a comparable output.
Some practitioners prefer to monitor peak weight velocity more frequently (e.g. every 3-4 months), as to not miss this stage of development. Peak weight velocity measures are similar to peak height velocity, but must be plotted after peak height velocity to ensure that mass is continually tracked after peak height velocity in both males and females.
Validity and Reliability
Measurements of mass are limited by some methods due to human error. For example, skinfold measures have been shown to have a high intra- and inter-observer reliability, which is made more difficult when there is high subject-variability, such as high levels of adipose tissue . Similar arguments are made with waist-circumference measures, where a lot of the results are predictive in nature, which limits the statistical significance of the test .
For truly accurate measures of mass, Bioelectric Impendence analysis (BIA) and Dual energy x-ray absorptiometry (DEXA) scans are the ‘gold standard’, but these can pose high financial cost, travel arrangements, and are somewhat invasive in a youth sample [3,11]. Alternatively, measurements on a reliable set of scales, taken at approximately the same time have proven to produce an accurate measure of the onset of peak weight velocity.
Future research should look to observe and report peak weight velocity to the same standards that peak height velocity has been described and interpreted by paediatricians and sports scientists. Moreover, future research should look to investigate:
- What non-invasive and financially accessible measures are reliable to measure peak weight velocity?
- How does peak weight velocity affect physical performance in both males and females during the process?
- How can practitioners alter training and potentially dietary needs during peak weight velocity to maintain health and safety?
Measures of weight should be taken roughly 2-3 times a year due to the magnitude and timing of peak weight velocity, which is different per-subject. An athlete of the same chronological age can be separated by as much as 5 years of biological development , which must be considered when collecting measurements. Therefore, monitoring weight, height, and cognitive function may provide a holistic view of the athlete at hand, allowing for a more individually tailored exercise regime.
The relative paucity of the research makes peak weight velocity a seemingly misunderstood phenomenon, which limits our true understanding of how youth athletes need to be programmed for during this period. Nevertheless, current recommendations are aligned to those of peak height velocity, which suggests that a suitable loading regime coupled with adequate supervision in sessions is safe and effective during peak weight velocity .
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About the Author
Tom Green MSc
Tom has an MSc in Applied Strength and Conditioning from Hartpury College, Gloucestershire. He has previously worked and supported professional and semi-professional rugby, Great Britain Equine, Semi-professional football and ran the Hartpury Women’s FC S&C programme for college and University athletes.
Follow Tom on Twitter @ThomasGreen_1