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New research has found that when it comes to estimating how active we are, not one of us gets it right, with Americans and older individuals in particular more likely to overestimate how much exercise they have actually done.

Led by the University of Southern California, the new study looked at individuals from three different countries, recruiting 540 participants from the United States, 748 people from the Netherlands, and 254 from England.

Participants were all asked to self-report their physical activity on a five-point scale (ranging from inactive to very active) and wore a fitness-tracker on their wrist for seven days so researchers could measure how active they really were during this period.

They found that Americans tended to think they were as active as the Dutch or the English, when in reality they were much less active than the European participants.

In fact, the percentage of Americans in the inactive category was nearly twice as large as the percentage of Dutch participants.

Americans also tended to rate themselves at the extreme ends of the scale, either as “very active” or “inactive,” whereas the Dutch and English participants were slightly more likely to rate themselves toward the “moderate” center of the scale.

Older people also thought they were as active as the young, when they were actually less active, with the fitness tracker data showing that in all three countries, people are generally less active as they get older.

However, inactivity was more common among older Americans, with 60 percent of these participants found to be inactive, compared to 42 percent of the Dutch and 32 percent of the English.

“Individuals in different age groups simply have different standards of what it means to be physically active,” said Arie Kapteyn, the study’s lead author. “They adjust their standards based on their circumstances, including their age.”

Kapteyn also added that he believes the differences in fitness perceptions are caused by differences in culture and environment.

For example, Americans are heavily dependent on cars to get around, whereas the Dutch frequently walk or cycle, to work and for daily errands, explained Kapteyn.

Kapteyn also added that because physical activity is so important for health, the findings of the new study could be important for future research.

“When you rely on self-reported data, you’re not only relying on people to share a common understanding of survey terms, but to accurately remember the physical activity that they report,” says Kapteyn. “With the wide availability of low-cost activity tracking devices, we have the potential to make future studies more reliable.”

The results can be found published online in the Journal of Epidemiology & Community Health. JB

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