Tag Archives: sedentary lifestyle

How much exercise is enough?

My guilty pleasure is Quora, which I dip into if a question intrigues me. Sometimes I “archive” the more interesting topics here.

“Is walking for 45 minutes a day enough to not have a sedentary lifestyle if you sit behind a desk for 7 hours a day?“

Medically, we don’t really have a clear, single definition of “sedentary lifestyle,” beyond knowing that a society in which a large number of people work in a sitting position means people do need to make purposeful effort to ensure they have adequate movement during the day. Most studies and government-issued guidelines around sedentary behavior cite health risks as being more common above a threshold of around … 7 hours a day (perhaps the reason you mention that number), although some suggest it is lower.

There are, of course, definitions of sedentary behaviors, and there are studies of health outcomes with respect to different kinds of sedentary behaviors. For example, there is research showing that hours of television watching is associated with poorer health outcomes, but the evidence for sitting to do other activities “behind a desk” (more cognitively demanding, such as work or using a computer for something other than just watching video) is not as negative, so we can’t even necessarily think of the mere fact as sitting across time as defining a “sedentary lifestyle.”

In the US, the guideline for adequate weekly activity to improve health outcomes works out to about 25 minutes a day of walking – less for vigorous exercise like running. The data we do have about exercise indicates that health benefits continue to accrue as exercise level increases, to a point that far exceeds 45 minutes a day. For people who like evolutionary explanations, investigators who work with societies that still practice hunter/gatherer lifestyles tend to find they are active on the order of 3 to 5 hours a day, of which over an hour is moderate to vigorous physical activity, so about triple the recommended level, and almost double 45 minutes a day. Very importantly, their activity levels don’t drop off with age as much as the activity levels of people living in westernized societies; they remain quite active throughout the life course.

This still leaves us with the question of what we should aim for. Studies that look for associations with better outcomes at different levels of steps per day keep finding more up to about 16,000. At that level, it’s hard to analyze effectively because there are not enough people who do it, or not enough people with different characteristics who do it. For example, it is possible that people who routinely walk more than 2 hours a day are different in many ways from people who walk 5,000 to 10,000 steps a day, and so it would not be possible to compare the two groups solely on the basis of walking volume.

From what we do know, 45 minutes a day, assuming that covers at least 5000 steps, will certainly be helpful, and it greatly exceeds the US activity guidelines (which are more of a starting point than a limit). More is almost always better. From a healthy aging perspective, being active consistently and daily – and including some strength training – is a key to a higher quality of life, and greater independence, for longer.

My answer on Quora

Sitting or standing, which is best?

My guilty pleasure is Quora, which I dip into if a question intrigues me. Sometimes I “archive” the more interesting topics here.

“Is sitting or standing better for health, and in what amount? I’ve seen articles suggesting both.“

The idea behind recommending more standing rests on the high modern prevalence of being expected to be seated quietly for long stretches of time, and the observation that this is associated with poorer health outcomes. Newpapers and magazines know that a lot of their readers have sedentary jobs, so they tend to emphasize the results that recommend less sitting. Standing does involve more activity for the body in term of maintaining balance, and so on, but standing for long periods, especially with minimal movement otherwise, is also associated with health risks.

The research question, for the people doing the studies, has never really been “What should a person do all day, sit or stand?” Or at least, I don’t think any investigators have seriously asked that question. The questions investigators ask have always been more like “Hmm, it looks like people who sit a lot have more heart disease than people who are on their feet a lot [eg, in the classic London Transport Workers Study (1949–1952), comparing drivers and conductors] – what is the specific mechanism for this? How much is too much? Are there easy ways to mitigate this for people in jobs requiring being seated” and, separately, “Prolonged standing is associated with back pain and vascular problems in the lower leg – what are the specific mechanisms here? How much is too much? Are there easy ways to mitigate this for people in jobs requiring long durations of standing?”

Studies are usually constructed to address very specific questions. The idea is to make the participants in the control and treatment groups as similar as possible so you can identify a dose-response relationship: you know the thing is having an effect, because different amounts (or the presence vs absence of it) are reliably associated with a particular outcome. But you want to minimize “confounding” – factors that could be contributing to a different outcome and whose relationship to the treatment are unknown or hard to determine. In practice, that may result in exclusions or controls that are strict enough to make generalizing to actual real-life behavior quite difficult. For example, the studies of pharmaceuticals that are submitted to the FDA to support approval, even those intended for use in very serious conditions, often exclude participants who are using a large number or specific forms of other medications, even though in real life, anyone eligible for the medication under study might also need those other medications. Studies are, therefore, best thought of as contributions to an overall picture, rather than definitive answers to broad questions.

It is common for a new study with surprising results or for the most recent very large study of a specific question to be reported in general-audience media more or less on their own, with little if any context. General-audience publications often report the latest results in isolation, creating the impression that “they” used to say one thing, and now “they” are saying another, when that is very rarely the case. It’s also common for general-audience publications to see things in terms of two sides or some other binary opposition (“sitting is bad, so you should stand instead”). But from the point of view of clinical practice, a single study is only valuable as a point of information in a larger whole. If the conclusion is surprising, investigators don’t usually think “see, everyone was wrong before!” They think, “maybe there is another question we should be asking so we can tell the difference between when we can expect this result and when we can expect the other result that this seems to contradict.” That interplay rarely makes it into a newspaper article or blog post.

Most clinicians will tell you that when it comes to almost anything, “the dose makes the poison.” It’s good to drink plenty of water, for example, but it is possible to drink too much and have serious health consequences. That is true of standing and sitting as well. Doing too much, especially with minimal other movement, of either one is associated with poorer health outcomes. That said, a lot of people don’t really have the flexibility to switch between sitting and standing during their work day, so telling people to mix them up is not very helpful. Fortunately, there is another set of guidelines that can help all of us: getting at least the minimum (ideally more) recommended physical activity – a combination of sustained activity, like walking or running, and muscle-strengthening activities, like climbing, pushups, or lifting weights.

My answer on Quora
US Physical Activity Guidelines