Ask R7

Q: "I have a regular exercise routine in the early mornings...but I also like to do an hour on the treadmill in the evenings, usually about 45 minutes after dinner. I have heard recently that exercising after meals does not do any good due to insulin levels, etc. The body is busy digesting food, so it ignores fat burning. Is this true? And am I wasting my time?I am 66 years old." A: No, you are not wasting your time. First, the predominant fuel used during exercise does not affect fat loss; in fact, studies have shown that even sprint training (which uses very little fat as fuel) will cause fat loss, because it creates an energy deficit.

"Your total daily energy expenditure is what matters when it comes to fat loss," says James Krieger, a 20/20 Lifestyles Research associate at the Pro Sports Club in Bellevue.

"It doesn't matter whether you exercise before or after meals. Yes, if you exercise after a meal, you will burn less fat during the exercise, but you will make up for that by burning more fat at other times of the day."

Also, exercise tends to suppress insulin levels, so you do not need to worry about the elevated insulin caused by a meal, Krieger says.

Q: Several readers had questions about the purpose of sub-maximal training, the value of training at roughly two-thirds of your maximum heart rate for 30 minutes and about the rough equation to use for getting there: 220 minus your age.

A: Dr. Tom Robertson, a pulmonologist at the University of Washington Medical Center, replies: "The heart-rate goals are all based on the assumption that 220 minus age predicts your maximum heart rate. On the average, that is true, but there are huge differences among normal persons, and the only way to determine maximal heart rate is to do a maximal-exercise test with cardiac monitoring."

Unfortunately, those can be expensive and something insurance doesn't cover.

One 60-year-old reader wrote in and said the equation made his maximal rate 160 and working at two-thirds of that is too easy. Robertson said he might have an actual maximal heart rate of 190, be well-trained and able to exercise at 85 percent of his top heart rate. "If he is already doing that, I suspect he is in no danger and could continue doing what he is doing."

The doctor says the greatest "objective decrease" in cardiovascular risk comes when absolutely sedentary folks start doing even a modest three- or four-times-a-week session of moderate-level (walking 3 mph), 30-minute exercise sessions. And working at a sub-maximal level allows you to work out longer.

"Training up to higher levels of fitness gives additional benefit, but less dramatic effects," he says.

Robertson cautions that the heart rate can rise with heat alone.

"I've seen big, fit athletes on the bike or treadmill increase their body temperature by 2 or 3 degrees Fahrenheit with five minutes of maximal-effort exercise," he says. "We are all heat engines, and the higher the level of exercise, the more heat is generated by our working muscles. That's what puts the big football linemen at such increased risk of heat injury: huge power outputs to move their bodies, and they are unable to radiate heat like the skinny little distance runners."

Who should invest in a heart-rate monitor? Competitive athletes who train an hour or two per day, he says.

Richard Seven is a Pacific Northwest magazine staff writer. He can be reached at rseven@seattletimes.com. Paul Schmid is a Seattle Times news artist.