Hickory dickory dock, the mouse ran on a treadmill

We often look to scientific studies for conclusions. But in the latest example of how ill-advised that can be, two research teams that studied how time of day affects the benefits we reap from exercise arrived at different findings. One group observed that morning exercise offers “a more robust impact” than an evening workout, whereas the other group “found exercise performance is better in the evening,” according to the papers, both published in Cell Metabolism. The studies underscore the role of the circadian clock in exercise efficiency, but they examined changing levels of different molecules and body processes — only capturing some of the ways the body responds to exercise. Plus, most of the research was done in mice, and trying to draw conclusions about human fitness by forcing a mouse onto a treadmill is not the best route for trying to decide whether to go for your run in the morning or evening.