Why Do Children Never Get Tired?

From hours on end in the playground to powering up steep hiking trails, children are infamous for their seemingly limitless energy levels. Now, researchers claim they've uncovered the secret. According to a new study published in open-access journal Frontiers in Physiology, children are armed with fatigue resistant muscles capable of recovering from high-intensity exercise with the same efficiency as elite endurance athletes.

Kids armed with fatigue-resistant muscles

As well as revealing new insight into the infinite energy levels of children, researchers assert the study can also be used to improve knowledge of optimising a child's athletic potential. The findings could also offer a new perspective on how the ageing process contributes to the risk of developing diseases like diabetes.

"During many physical tasks, children might tire earlier than adults because they have limited cardiovascular capability, tend to adopt less-efficient movement patterns and need to take more steps to move a given distance," explains co-author Sébastien Ratel, Associate Professor in Exercise Physiology at France's Université Clermont Auvergne. "Our research shows children have overcome some of these limitations through the development of fatigue-resistant muscles and the ability to recover very quickly from high-intensity exercise."

Kids outperform elite athletes

The study drew on data sourced from three research groups – young boys, untrained adults and national-level endurance athletes. Each group was asked to perform high-intensity cycling tasks, then analysed for energy output and post-exercise recovery rates. Factors included heart-rate, oxygen levels and lactate-removal rates. The researchers explored the production of aerobic energy, which draws on oxygen from the blood. They also looked at anaerobic energy, which produces acidosis and lactate and is often associated with muscle fatigue. In all tests, the boys aged eight to 12 outperformed the adults and rivalled the endurance athletes.

"We found the children used more of their aerobic metabolism and were therefore less tired during the high-intensity physical activities," comments Ratel. "They also recovered very quickly -- even faster than the well-trained adult endurance athletes -- as demonstrated by their faster heart-rate recovery and ability to remove blood lactate."

Optimising athleticism and combating disease

When it comes to optimising the athletic potential of children, Ratel maintains that exceptional muscle endurance means the real benefits lie in developing technique, muscle strength and attitude. He also stresses that in the wake of rising obesity and disease rates related to physical inactivity, the study could offer valuable insight into physiological changes that contribute to diseases like diabetes.

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