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“For at least some if not many of the mechanisms associated with health, some reasonable [exercise] frequency is required; [examples are] blood pressure and insulin resistance….Just sitting as most people do [between workouts] is health detrimental.” Richard Winett, PhD, Director, Center for Research in Health Behavior, Virginia Tech
“Sedentary pursuits represent a unique aspect of human behavior and should not be viewed as simply the extreme low end of the physical activity continuum.” Peter T. Katzmarzyk, PhD, et al, Medicine & Science in Sports & Exercise (Volume 41, 2009)
Too Much Sitting Is Risky—Even for People Who Train
Once-a-week Training Downside
Last month, we discussed the pros and cons of the Body by Science 12-minutes-once-a-week workout plan: http://www.cbass.com/AerobicsNeedIt.htm We promised to talk about the importance of staying active between workouts this month. As luck would have it, our timing was excellent.
Who would’ve thought that too much sitting would suddenly become a hot topic for researchers? That’s what has happened.
How much time do you spend riding in a car, working at a desk, eating at a table, playing video games, using a computer, watching TV, or engaged in other sedentary pursuits? Think about it. It may be a problem. Even if you exercise regularly.
I remember reading in Strength & Health years ago that Terry Todd, arguably the best power lifter in the world at the time and editor of the magazine, was working from bed to enhance recovery between his brutal workouts. In my mind’s eye, I can still see the photo of 300-pound Todd with papers spread all over his bed. The plan must’ve not worked out very well, because I never read or heard any more about it. Abandoning the practice may have been far wiser than he knew.
I’ve long maintained that walking or staying active in other ways between workouts makes you feel good, burns extra calories, and helps speed recovery. Turns out that's not the half of it.
A Unique Risk Factor
Neville Owen (School of Population Health, University of Queensland, Brisbane, Australia) and two colleagues comment in the British Journal of Sports Medicine (2009:43;81-83) that the widely recommended 30 minutes of moderate to vigorous activity 3 to 5 days a week may not alone be sufficient. “Recent evidence underlines the importance of also focusing on sedentary behaviors—the high volume of time that adults spend sitting in their remaining ‘non-exercising’ waking hours,” they write.
Calling too much sitting a new field of concern, they continue: “Our recent body of work has identified sedentary behavior (time spent sitting) as a novel and potentially important risk factor for development of chronic disease…There may be significant metabolic and health effects from prolonged sitting—the activity that dominates most people’s remaining ‘non-exercise’ waking hours.” (Weight gain and blood glucose control are two areas of concern noted in the editorial.)
The researchers say that most adults spend more than half of their waking hours in sedentary activities (mostly sitting), with the remainder of the time spent in light intensity activities (standing with some movement); “only about 4.5% of the day is spent in moderate to vigorous physical activity.”
That sounds about right, doesn’t it?
The 12-minute weekly workout discussed here last month is more intense than these researchers have in mind, but it would fall well short of the energy expended during 0.7 hours/day (4.5% of waking hours) of moderate to vigorous daily exercise.
Owen and colleagues say we need to begin thinking about ways to break periods of prolonged sitting. “Commonsense might suggest that it may be prudent to try to minimize prolonged sitting with 5 minute breaks every hour,” they suggest.
Taking regular activity breaks is also likely to increase productivity; see Intervals for Fitness—and Life: http://www.cbass.com/Intervalsforlife.htm
Several excellent studies have investigated the health risks involved in too much inactivity. Let’s look at two of them, starting with a study of the relationship between sitting time and mortality from all causes. (Dr. Richard Winett called my attention to both studies.)
Sitting Time and Death Risk
Peter T. Katzmarzyk, PhD, and colleagues from Canada and the U. S. followed 17,013 Canadian men and women 18-90 years of age for an average of 12 years, looking into the relationship between sitting time and deaths from all causes, and from cardiovascular disease (CVD). Deaths during the period studied totaled 1832, including 759 from CVD. Their report appears in Medicine & Science in Sports & Exercise ( 41, 5, 998-1005, 2009).
Subjects were grouped based on the portion of the day spent sitting (almost none, one fourth, half, three fourths, and almost all day). Participants were also classified as active or inactive based on current minimum physical activity recommendations.
What they found is a wake-up call, especially to those complying with recommended exercise guidelines.
They found a progressively higher rate of mortality (all cause and CVD) as sitting time increased. For example, participants who spent three fourths of their day sitting were 36% to 47% more likely to die than those who spent only one fourth of the day sitting. Importantly, it didn’t make any difference whether subjects were otherwise active or inactive; death rates were essentially the same for those who exercised regularly and those who didn’t exercise.
The researchers concluded: “These data demonstrate a dose-response association between sitting time and mortality from all causes and CVD, independent of leisure time physical activity.”
“This is an important observation,” the researchers wrote in the Discussion portion of the report, “because it suggests that high amounts of sitting cannot be compensated for with occasional leisure time physical activity even if the amount exceeds the current minimum physical activity recommendations.”
In other words, regular weekly exercise (12 minutes or two-and-a-half hours) does not allow us to sit around without consequences.
Now, let's look at a study that highlights two ways that staying active between workouts may help.
Walking and Cardiovascular Health
A study reported in the Scandinavian Journal of Medicine and Science in Sports (2008; 18: 736-741) investigated the independent effect of walking on two markers of cardiovascular health. The researchers are M. Hamer and A. Steptoe, both from the Department of Epidemiology and Public Health, University College London, London, UK.
It has been suggested that walking may have unique positive effects on inflammation and hemostasis, both markers of cardiovascular health. Inflammation is a central factor in atherosclerosis or hardening of the arteries; see http://www.cbass.com/Inflammation.htm . Hemostasis refers to blood thickness (flow/sluggishness) and is also an important factor in atherosclerosis. With both markers, less is better.
The aim of the Hamer-Steptoe study was to examine the impact of walking on inflammation and hemostasis, separate and apart from vigorous physical activity.
The researchers recruited 185 healthy volunteers, 107 men and 78 women, age 45 to 59. The participants were asked how many minutes they walk each week and how often they engage in vigorous activities, such as running, that makes them feel out of breath. The researchers also took blood samples and analyzed them for markers of inflammation and hemostasis.
Walking 30 minutes or more a day was found to be significantly associated with lower inflammation and hemostatic markers. Vigorous activity was associated with lower levels of hemostatic markers, but not lower inflammatory markers.
Walking appeared to lowered both markers, with the positive effect on inflammation being unique. Walking lowered inflammation, but vigorous exercise did not. Both walking and vigorous exercise improve blood flow.
Assuming that the association is causal, the researcher estimated that “meaningful reductions in levels of hemostatic and inflammatory markers could be achieved by walking 30 min/day.”
They concluded that “regular walking is associated with lower levels of hemostatic and inflammatory markers, independent of vigorous physical activity.” In other words, walking does the job with or without vigorous exercise. We know, of course, that intervals and other forms of vigorous exercise have many other benefits; see Short, Hard Intervals Improve Insulin Action.
(Vigorous exercise increases inflammation, at least temporarily. As explained in my book Challenge Yourself, inflammation is part of the normal healing process. Walking, it would seem, helps to moderate the inflammation caused by vigorous exercise. The two forms of exercise apparently complement one another. They might even be termed a dynamic duo.)
Bottom line: Those who engage in vigorous exercise--especially those who train only once a week--would be well advised to walk or engage in some other form of moderate physical activities on most intervening days. I’m going to keep walking or staying active in other ways between workouts. I’m also going to make it a point to get up and move around periodically when working at my desk or the computer.
How about you?
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