After I strode from the gym the other night and headed directly to yet another holiday party, I dove into the bonbons, éclairs and eggnog with confidence: Not only had I obliterated 500 calories on the treadmill but I knew -- hey, I read it on the Internet! -- that my body was continuing to burn calories at a higher-than-normal rate even after my workout. But waddling home afterward, I wondered about the extent of that so-called after-burn, formally known as excess post-exercise oxygen consumption (EPOC).
"The magnitude of the effect is exaggerated," said Cedric Bryant, chief exercise physiologist for the American Council on Exercise. Bryant, who holds a PhD in physiology, has reviewed numerous studies on EPOC and concludes that after-burn -- which can last from two to 15 hours after a workout, depending on exercise intensity -- amounts to about 10 to 15 calories for every 100 calories burned during the actual exercise.
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"If you go the gym and burn 300 calories, your after-burn will be around 45 calories. That's one bite of a Snickers bar," Bryant said. (Ouch. At least he didn't say 'bonbon'.) "People should not look at this as a license to eat and drink all day thinking that their earlier workout is melting calories away."
After-burn, however minuscule, is at least real. Conrad Earnest, director of the Center for Human Performance and Nutrition Research at the Cooper Institute in Dallas, explains that during exercise, especially at higher intensities, "your muscles require more energy than can be obtained from oxygen alone during elevated exertion. In essence, they create an oxygen deficit."
When you finish exercising, areas of the body that are in oxygen deficit work to recover what they loaned to the muscles; the body works to restore hormone balance and to cool down. All of that requires oxygen, and EPOC occurs until the body restores resting-state balance.
Both experts agree that, for typical exercisers, how you burn the calories -- running, weight lifting, reindeer herding -- does not significantly affect after-burn. However, key studies have shown an elevated EPOC effect for people who lifted very heavy weights: 90-minute sessions of lifting to failure, compared with lighter lifting or mid-intensity cardio work.
But, Earnest notes, such heavy lifting "is not what the average soccer mom is doing in the gym" -- nor what she's likely to do to justify that extra bite of a candy bar.
Intensity does affect after-burn, but not to the extent some Web sites claim. An oft-cited 1997 study published in the Journal of Applied Physiology showed higher after-burn for people running at 70 percent of maximum oxygen consumption, spiked with even higher-exertion intervals, than for people exercising steadily at 40 percent of their max. But, the study's authors cautioned, "the major contribution of both [study groups] to weight loss is via the energy expended during the actual exercise," not the after-burn.
We're serving bonbons and oxygen for the last Moving Crew chat of 2004. Join us this Thursday from 11 a.m. to noon: www.washingtonpost.com/wp-dyn/liveonline/health/movingcrew.
-- John Briley