According to a new study published in the International Journal of Obesity, children become less and less active with each year of elementary school.

Researchers at the University of Bristol monitored more than 2,000 children from 57 schools in South West England, by having the children wear an accelerometer for three school days and two weekend days. The data they collected gave the researchers an accurate representation of how many minutes per day the children engaged in physical activity. Specifically, the researchers measured moderate to vigorous physical activity (MVPA), measured as being enough to break a sweat and cause the children to become slightly out of breath.

The study showed that children become, on average, 17 minutes less active per week, with each year of elementary school. In year one, 61% of children participated in at least one hour of MVPA per day. By year six, the number dropped to 41%.

For girls alone, the drop in physical activity was especially significant. By the time they finished elementary school, their activity level dropped from 54% to 28%. On average, children lost more than an hour of exercise per week between the ages of 6 and 11 years old. The study showed that children were even less likely to be active on the weekends.

While this study was conducted in the UK, it’s widely known that American children are facing the same problems; inactivity, paired with a diet full of sugar and processed foods, contributes to the childhood obesity epidemic plaguing the nation.

Inactivity and obesity are markers for many chronic diseases that can cut life short. For tips on how to get your kids moving and how to create a healthy eating environment for kids, read this article on the crisis of childhood obesity.