The changes in physical fitness that occur throughout childhood and adolescence are largely the result of changes in body size and composition, particularly changes in lean muscle and fat mass, that accompany maturation. There are noticeable differences between boys and girls for some components of fitness, and the timing and tempo of the adolescent growth spurt can have a significant impact.
Body composition, maturation and effects on performance
In boys, body size and composition changes significantly throughout childhood and adolescence with increases in fat-free mass and decreases in fat mass. These patterns of change in body composition are similar in both girls and boys before puberty, but it’s after puberty that differences in males and females emerge.
A number of changes occur around the growth spurt (PHV), boys get broader shoulders, and bigger arms, whereas girls get wider hips. These differences are driven by significant hormonal (androgen) increases in boys compared to girls, resulting in rapid increases in fat-free mass, and decreases in fat percentage. At the end of the adolescent growth spurt, boys fat-free mass is 25-30% greater than girls fat-free mass, and their percentage of body fat is about half that of girls.
This explains much of the difference between the physical performance of males and females during adolescence and into adulthood, with males advantaged by greater gains in muscle mass and lower gains in fat mass.
Motor performance
When it comes to strength, boys demonstrate a steady increase in maximal strength from childhood to adulthood. Girls, on the other hand, exhibit similar gains in strength as boys prior to puberty; however, unlike boys, their strength levels tend to plateau during mid to late adolescence.
Boys tend to outperform girls in various fitness measures, including strength, strength endurance, power, speed, and overall endurance. These differences tend to increase with age, suggesting a maturational impact on all fitness components.
These improvements appear to be relative to the timing of the adolescent growth spurt, and tend to be aligned around peak height velocity. However, the rate of these improvements depend on the activity performed.
In boys, increases in strength and power typically happen 6 to 12 months after reaching peak height velocity. In contrast, flexibility tends to improve 6 months prior to peak height velocity, while enhancements in speed are observed 18 to 24 months before peak height velocity.
It’s important to remember that the timing and tempo of the adolescent growth spurt can vary so much between individuals, and there are often big variations in performance between early, and late developers
This is where grouping children by school years based on their chronological age can lead to issues, particularly since it often favours those who mature earlier. While this method may benefit teachers and coaches looking to select the largest, strongest, and fastest kids for sports teams, we must question whether this is the most effective strategy and consider the impact it has on those who develop later.
Well interestingly, not only do late developers eventually catch up with their early maturing peers, but they also tend to significantly outperform their early maturing peers in functional and explosive strength in adulthood, which suggests there may actually be some long-term benefits for later maturing individuals
The common practice of placing children into age groups for sport may acutely benefit those who are more developed physically, emotionally, and cognitively. However, those who are born in the later stages of the year appear to experience an unintentional bias in their long-term sporting success.
It is important that teachers and coaches are aware of a ‘Relative Age Effect’, where being born at a certain time of the year holds a distinct advantage in sport and academic success. In other words, those born later in the year appear to be at a disadvantage because they are typically physically, emotionally and cognitively less developed than other children.
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