GOOD

The Science Behind Why Kids Can Run Around All Day

They’re more like adult endurance athletes than we once thought.

Most of us know children who can run and play for hours and hours, taking only short rests. As a parent or caregiver, it can be exhausting.

For scientists, why this is the case has long been the source of debate — is it due to fitness? Or something else?


Our study published in April looked at performance and recovery of children and adults doing strenuous cycling. It shows children not only out-perform most adults, but can perform as well as highly-trained adult endurance athletes, and then recover even faster afterward.

Tired from parenting? Blame your muscles. Image via The Conversation/Shutterstock.

Children’s muscles are different

Repeated experiments have shown that the muscles of children tend to fatigue more slowly than adults’.

These results seem to fly in the face of what science would predict. For example, children have shorter limbs, so they have to take more steps and should therefore theoretically use more energy.

Children are also less able to make use of tendon energy return systems — that is, they store less energy in their tendons so they can’t reuse this energy to propel themselves during movement.

And children show greater activity in muscles that oppose or control movement, a reflection of the fact that typically they are less skillful and therefore, use more energy.

So, how do their muscles stay fresh?

Aerobic and anaerobic exercise

One possible explanation for the remarkable muscle endurance of children could be their different use of energy pathways.

Anaerobic (“oxygen-independent”) pathways produce large amounts of energy without the need for oxygen but tend to cause rapid fatigue. For example, sprinters rely on anaerobic metabolism to run fast over short distances.

Aerobic (“oxygen-dependent”) pathways tend to produce energy at a slower rate but allow us to work for many hours without muscle shutdown, like in a well-run marathon.

We know from existing research that children seem to be able to get more of their energy from aerobic pathways than adults, minimizing the fatiguing anaerobic contribution. Their aerobic machinery also kicks into gear faster than adults, so they don’t need to rely as much on anaerobic metabolism when exercise first starts.

These benefits are believed to partly result from children having a greater proportion of so-called “slow-twitch” muscle fibers, which have a greater activity of important enzymes that drive the release of energy from aerobic pathways.

Such findings prompted us to speculate that children’s muscles might actually respond to exercise in a similar way to adult endurance athletes’, since they too show these characteristics.

Let’s go cycling

We tested our speculation in a study run by researchers at Université Clermont Auvergne, in France.

Children (average age 10.5 years), young adults (21.2 years) with a similar physical activity level as the children, and age- and height-matched endurance-trained male athletes (21.5 years) were asked to complete two cycling tests on a stationary bicycle.

In the first test, power output was continually increased until exhaustion. In the second test, the subject completed a 30-second all-out cycle sprint. These tests allowed us to measure numerous physiological responses to exercise and assess both the rate of fatigue and then recovery specifically during brief, maximal-intensity exercise.

We found that the children fatigued as much in the all-out cycle as the endurance-trained athletes (about 40% loss of power) and much less than the untrained adults (about 50% loss).

Data also show that the proportion of energy derived from aerobic pathways in the 30-second cycle sprint was similar in the children and athletes, and more than in untrained adults.

These results clearly show that fatigue rates in response to high-intensity exercise may be the same in children as they are in highly-trained adult endurance athletes and that this is associated with an incredible generation of energy from aerobic energy pathways.

But data collected during recovery from the exercise also revealed startling outcomes. The rate at which oxygen use declined after the exercise was the same in children and athletes. The rates at which heart rate returned to normal and lactate (a compound associated with muscle fatigue) cleared from the blood were even faster in the children, and again, much faster than in untrained adults.

These data show that children’s muscles recover rapidly from high-intensity exercise, possibly revealing why children are able to produce repeated exercise efforts when most of us adults continue to feel exhausted.

How children’s muscles work

Such data provide strong hints as to how to optimize exercise and sporting performance in children.

Children might benefit from short, high-intensity exercise bouts to boost anaerobic capacity and a focus on movement skill, muscular strength, and other physical attributes more than in adults.

Adults (and adolescents), on the other hand, may need to place a greater emphasis on improving their muscle aerobic capacity.

There may also be important health implications. Metabolic diseases, including diabetes and many forms of cancer, are increasing in prevalence in adolescents and younger adults but are still rarely seen in children. It might be the case that the loss of muscle aerobic capacity between childhood and early adulthood is a key maturation step that allows metabolic diseases to take hold.

It will be interesting in the future to examine the link between muscle maturation and disease and test whether the maintenance of our childhood muscles through exercise training might be the best medicine to prevent disease.

Either way, at least we now have some idea as to why children are able to play and play and play when we adults need to take a break. Kids are already elite.

Sports
Ottawa Humane Society / Flickr

The Trump Administration won't be remembered for being kind to animals.

In 2018, it launched a new effort to reinstate cruel hunting practices in Alaska that had been outlawed under Obama. Hunters will be able to shoot hibernating bear cubs, murder wolf and coyote cubs while in their dens, and use dogs to hunt black bears.

Efforts to end animal cruelty by the USDA have been curtailed as well. In 2016, under the Obama Administration, the USDA issued 4,944 animal welfare citations, in two years the numbers dropped to just 1,716.

Keep Reading Show less
Science
via I love butter / Flickr

We often dismiss our dreams as nonsensical dispatches from the mind while we're deep asleep. But recent research proves that our dreams can definitely affect our waking lives.

People often dream about their significant others and studies show it actually affects how we behave towads them the next day.

"A lot of people don't pay attention to their dreams and are unaware of the impact they have on their state of mind," said Dylan Selterman, psychology lecturer at the University of Maryland, says according to The Huffington Post. "Now we have evidence that there is this association."

Keep Reading Show less
Health
via Real Time with Bill Maher / YouTube and The Late Late Show with James Corden / YouTube

A controversial editorial on America's obesity epidemic and healthcare by comedian Bill Maher on his HBO show "Real Time" inspired a thoughtful, and funny, response by James Cordon. It also made for a great debate about healthcare that Americans are avoiding.

At the end of the September 6th episode of "Real Time, " Maher turned to the camera for his usual editorial and discussed how obesity is a huge part of the healthcare debate that no one is having.

"At Next Thursday's debate, one of the candidates has to say, 'The problem with our healthcare system is Americans eat shit and too much of it.' All the candidates will mention their health plans but no one will bring up the key factor: the citizens don't lift a finger to help," Maher said sternly.

Keep Reading Show less
Politics

There is no shortage of proposals from the, um, what's the word for it… huge, group of Democratic presidential candidates this year. But one may stand out from the pack as being not just bold but also necessary; during a CNN town hall about climate change Andrew Yang proposed a "green amendment" to the constitution.

Keep Reading Show less
test
Me Too Kit

The creator of the Me Too kit — an at home rape kit that has yet to hit the market — has come under fire as sexual assault advocates argue the kit is dangerous and misleading for women.

The kit is marketed as "the first ever at home kit for commercial use," according to the company's website. "Your experience. Your kit. Your story. Your life. Your choice. Every survivor has a story, every survivor has a voice." Customers will soon be able order one of the DIY kits in order to collect evidence "within the confines of the survivor's chosen place of safety" after an assault.

"With MeToo Kit, we are able to collect DNA samples and other tissues, which upon testing can provide the necessary time-sensitive evidence required in a court of law to identify a sexual predator's involvement with sexual assault," according to the website.

Keep Reading Show less
Health