Comparatively speaking, young people in the United States and England do not move much. Studies indicate that most children reach their activity peak at about age 7 and become more sedentary throughout adolescence. Many parents probably hope that shiny new technologies, such as Fitbits and other physical-activity monitors, might inspire our children to become more active.

But a recent study published in The American Journal of Health Education finds that the gadgets frequently have counterproductive impacts on young people’s attitudes about exercise and the capabilities of their own bodies.