It's hard to fight nature. We mammals have an instinctual urge to hibernate when the mercury starts dropping, and thanks to activity trackers we have some data to prove that theory holds true (if we actually get that sleep is another story). By correlating pedometer stats culled from "hundreds of thousands" of Jawbone Up users with weather info from their respective areas, the outfit was able to discern that there's an ideal temperature range for physical activity. Because people typically have to get up and around during the work week, Jawbone instead focused its study on weekends. You know, when we have an actual choice of whether or not we're going to get off the couch.