The other men began a typical moderate-exercise program, riding bikes at the lab five times a week at a pace they could comfortably sustain for 30 to 40 minutes.
Over the course of the next six weeks, the HIIT group pedaled intensely for a grand total of less than an hour, while the moderate-intensity group worked out for at least 2.5 hours each week for the same period.
At the end of the six weeks, both groups returned to the lab for re-testing, after which the scientists combed through their results for disparities. They found plenty.
The men almost all were fitter, and to about the same extent, however they had exercised. But only those in the moderate-exercise group had shed much body fat, improved their blood pressures or become better able to metabolize the extra fat from the unctuous shake.
Perhaps most interesting, everyone’s blood-sugar control at home was best only on the days when they exercised, meaning three times a week for the HIIT riders and five for the moderate group. On the remaining days, blood sugar levels tended to rise.
Taken as a whole, the results indicate that intervals and traditional exercise alter our bodies in divergent ways, and we may want to consider what we hope to achieve with exercise when choosing how best to exercise, says Jamie Burr, a professor at the University of Guelph, who conducted the new study with his graduate student Heather Petrick and other colleagues.
“All exercise is good,” Dr. Burr says. But “there are nuances.” Frequent, almost-daily moderate exercise may be preferable for improving blood pressure and ongoing blood-sugar control, compared to infrequent intervals, he says, while a little HIIT is likely to get you in shape as effectively as hours and hours of easier cycling or similar exertion.
Of course, this study was small-scale and short-term and involved only overweight, out-of-shape men, so we cannot be sure the findings apply to the rest of us. But the primary lesson seems widely applicable. “Move often,” Dr. Burr says, meaning if you HIIT today, walk tomorrow, and repeat.