What’s the fastest a human can grow?
If you have teenagers – or if you’ve been a teenager yourself – you’ve probably experienced this: Your kid’s jeans fit you perfectly in September, but by December they’re showing the ankle. The adolescent growth spurt can seem surprisingly rapid, with some adolescents growing 4 to 5 inches (10 to 13 centimeters) in a single year. But is this really the most rapid period of human growth?
Surprisingly, no: the adolescent growth spurt is only the second fastest humans can grow.
Babies can gain nearly 10 to 12 inches in height per year, more than double the growth rate even during the most dramatic adolescent growth spurts.
Indeed, for girls, “at 18 months, they will be 50% of their adult height”, Adam Baxter Jonesprofessor at the College of Kinesiology at the University of Saskatchewan in Canada, told Live Science. Boys reach 50% of their adult height by 24 months, he said.
Then things slow down. “As we get to late infancy and childhood, physical growth gets put on the back burner,” Cumming said.
Growth drops to about 2 to 2.5 inches (5 to 6 centimeters) per year from age 4 until puberty, according to Baxter-Jones. This is when humans reach their second fastest growth period.
At their peak during puberty, girls grow an average of 3.5 inches (9 centimeters) per year, and boys grow an average of 4 inches (10 centimeters) per year, according to a puberty study. Journal of Adolescent Health.
But these average peak growth rates are just that: averages.
“If we measure regularly enough, we see periods of really, really intense growth, and then the body adapts afterward,” Cumming said. “We can see rates up to about 20 centimeters [nearly 8 inches per year] in some of the studies we looked at… of course, if you average over a period of time, [you get] 10 to 12 centimeters [4 to almost 5 inches] per year.”
Just like when they were babies, girls experience their growth spurts earlier, around age 11, while boys typically enter puberty about two years later.
“Boys will generally have a slightly more intense growth spurt,” Cumming said. “This is because they produce more growth hormone, but also testosterone, which also contributes to bone length.”
The pubertal growth spurt stops around age 16 for girls and 18 for boys – and because boys both have more intense growth and grow about two years longer, on average they end up taller.
The age at which a person hits their growth spurt does not affect their final height: a person who matures early stops growing earlier than a person who matures later, so a person who matures later has more growth. time grow up, Baxter-Jones said.
Growth spurts and body shape
Growth spurts occur from the outside in. “First it’s feet and hands, then long legs and long arms. That’s why you see kids right at the start of puberty, they look like baby giraffes. They have these big clown feet, these legs that last forever,” Cumming said.
The torso grows last – and if a child develops late, sometimes the torso never catches up with the rest of the body. As a result, in sports like ballet and gymnastics, teams select late developers because they have a more linear physique and longer legs, according to Cumming. However, early developers have their own sporting advantages.
“If you experience a growth spurt at puberty early, you’re bigger, stronger. These are the kids who get selected for all the top positions and into the top academies,” Cumming said. “Across Scottish academies we surveyed over a thousand children over 14. We found no late developers.”
But this rapid growth comes at a cost. During growth spurts, bones are weaker and more susceptible to damage.
“Your bones grow, and then they mineralize. There’s about a nine-month interval there,” Baxter-Jones said. “The fracture rate peaks during this adolescent growth spurt.”
Muscles and tendons also take up to nine months to catch up with bone growth, which can lead to growth-related injuries, particularly around the heel, knee and lower back.
However, careful monitoring of growth spurts can help prevent more serious problems. “If we do this in Premier League academies we can reduce these non-contact injuries by around 70 per cent,” Cumming said.
For parents wondering if their child’s growth pattern is normal, both experts stressed that a wide variation is expected.
“It’s okay to grow quickly, but it’s also okay to grow slowly,” Baxter-Jones said. Final adult height depends on genetics. There are also rare pathologies in children, such as pituitary gigantismwhich lead to excessive production of growth hormone. Children with this condition can grow up to 6 inches (15 cm) per year, and a report documented a 13-year-old boy growing 7.5 inches (19 cm) per year. But even this rapid growth is less than the rate at which babies grow.
So what is the fastest growth a human can do? The answer is not when you take off your jeans as a teenager, but when you’re too young to remember.
