For the 2013 study, 16 fit adults participated in a 20-minute bodyweight circuit, which included exercises like pushups, burpees, squats, and lunges. John Porcari, the lead researcher and head of the university’s performance lab, says the participants burned an average of 15 calories per minute, nearly twice the rate expended during a long run.

The key to the efficient burn is effort, says Porcari. “You should be feeling extremely uncomfortable. If you aren’t exhausted by the end of this workout, you aren’t doing it right.”

The researchers modeled the circuit after high-intensity interval training (HIIT), a workout style that includes periods of intense effort followed by a short recovery.

(Looking for a HIIT workout geared toward runners? Jordan Metzl, M.D., a marathoner and sports physician at the Hospital for Special Surgery in New York City, designed the training series IronStrength specifically to prevent running injuries and increase speed.)

In the study, participants completed an exercise all-out for 20 seconds then rested for 10, repeating the process in five, four-minute segments.

“What it all boils down to is overtraining specific metabolic systems,” says Porcari. “You can only run a race at a certain pace for so long. When you do high-intensity interval training, you shift that threshold up. It’s why athletes do intervals.”

For runners looking to incorporate a bodyweight HIIT routine in their normal training, Porcari recommends keeping it to once or twice a week, allowing plenty of time for recovery between sessions.