The four-second workout

The scientists reasoned that if athletes needed two seconds of pedaling to reach maximum exertion, the rest of us probably would require, say, twice as much. So, they asked their volunteers to clamber on the bikes and sprint as hard as possible for four seconds, then stop pedaling, rest for 45 seconds, and sprint again, repeating that sequence five times.

The volunteers completed these brief interval sessions once every hour for eight hours, for a total of 160 seconds of actual exercise that day. Otherwise they sat, then returned the next day to down the unctuous breakfast shake.

Their metabolic responses differed this time, though, the researchers found. The volunteers arrived at the lab with lower blood levels of triglycerides to start with and burned more fat during the next six hours, so their triglycerides remained about 30 percent lower throughout the six hours of monitoring than on the morning after nonstop sitting.