Sitting for long hours per day takes years off your life

Can someone exercise and still be a couch potato? That peculiarly modern question motivated a new study from Finland in which a group of healthy, physically active volunteers donned special shorts that measure muscular activity in the legs. The volunteers then went about their daily lives.

All were diligent exercisers. Some ran. Others lifted weights or played soccer. A few Nordic-walked. On one day during the study, they worked out as usual. On another, they did not exercise.

Throughout, the shorts measured how much they actually moved.

A growing body of science suggests that prolonged inactivity, a practice known more familiarly as sitting a lot, is both widespread and unhealthy. In a representative study published last month in The Archives of Internal Medicine, Australian researchers compared medical records and lifestyle questionnaires for more than 220,0000 Australian adults 45 and older.

They found that the more hours the men and women sat every day, the greater their chance of dying prematurely. Those people who sat more than eight hours a day — which other studies have found is about the amount that a typical American sits — had a 15 percent greater risk of dying during the study’s three-year follow-up period than people who sat for fewer than four hours a day.

That increased risk held true in the Australian study even if the people sitting eight hours a day spent at least part of that day exercising.

But that study and many others examining sitting and health have relied on self-reported measures of physical activity, like questionnaires. A few have used accelerometers to determine how many steps people were taking during the day.

No one, though, had directly studied people’s muscular activity during sitting and exercising, outside the artificial environment of an exercise physiology lab, until the Finnish researchers came up with the idea of embedding flexible electrodes into shorts fabric.

Measurement of muscle activity matters. In earlier studies with animals whose legs were immobilized with casts or traction devices, physiologists noticed swift, dramatic and deleterious changes in the levels of certain enzymes in cells throughout the animals’ bodies that affect fat metabolism and blood sugar regulation. The researchers concluded that the lack of muscular contractions in the animals’ legs had caused a chain of biological reactions that led to the alterations in enzyme production.

In the current Finnish study, after volunteers donned the shorts, the electrodes began constantly tracking contractile activity in the quadriceps and hamstring muscles, two of the largest sets of muscles in the body. The volunteers also completed detailed logs about their activities during the days of the study.

The researchers had hypothesized that they would see considerably less muscular inactivity over all on the days the volunteers exercised, says Taija Juutinen Finni, a professor of kinesiology at the University of Jyvaskyla in Finland, who led the study.

But the results did not turn out that way. There was, in fact, virtually no difference in how much time people spent being couch potatoes on the days when they exercised compared with days when they did not. On nonexercise days, about 72 percent of volunteers’ waking time, or about nine hours, was spent sitting.

When they formally exercised, volunteers used about 13 percent more energy over all than on days they didn’t exercise. But they still sat 68 percent of the time.

Surprisingly, how much people exercised or what kind of exercise they chose did not change sitting time. Whether volunteers worked out for less than an hour or for more than 90 minutes, they spent an equivalent amount of time the rest of the day being mostly torpid physically.

It seems that after exercising, the study authors concluded, people “substitute either lighter and/or sedentary activities.”

David W. Dunstan, a professor at the Baker IDI Heart and Diabetes Institute in Australia, who has studied inactivity and wrote an editorial to accompany the new Australian paper, says he found the study fascinating. By measuring muscular inactivity using electromyography, he says, “the measurement is getting closer to the heart of the sitting problem, that being a problem of muscular disuse.”

Dr. Finni agrees. Although she and her colleagues did not look directly at the downstream biochemical effects of the inactivity, she says, their results suggest that normal exercise, which fills so few hours of even active people’s days, “may not be enough in terms of health.”

Of course, exercise remains valuable, she and Dr. Dunstan are both quick to add. It reduces risks for cardiovascular disease and other conditions and burns calories.

But exercise paired with otherwise unalloyed sitting should be avoided, Dr. Dunstan says. “It is important the general public become more conscious about what they do in their nonexercise time,” he says. Almost everybody, he says, “should look for opportunities to reduce their daily sitting time and move more, more often, throughout the day.”

By GRETCHEN REYNOLDS, Columnist
NYTimes