30 Years of Aging vs 3 Weeks of Bed Rest – Which is Worse For Aerobic Fitness?

Image created using photos from goldberg and Bengt Neyman (Flickr)

I recently came across a very interesting study published in Circulation in 2001.  In it, authors Darren McGuire and colleagues perform the 30-year follow-up on a group of 5 men who had taken part in the Dallas Bed Rest and Training Study (DBRTS).  The DBRTS took place in 1966, when all 5 men were healthy 20 year-olds.  They were assessed extensively at baseline, following 3 weeks months of bed rest, and following 8 weeks of physical training. In 1996 these same 5 men were re-assessed, allowing the researchers to compare the influence of 3 weeks of bed rest and 30 years of aging on markers of fitness.

As you’d expect, there was a significant increase in both body weight and body fat percentage over the 30 year period.  But what I find more interesting is what happened to aerobic fitness.  Below are the results of the VO2 max tests at baseline, post bed rest, and after 30 years of aging (error bars represent standard deviation)

It looks as though 3 weeks of bed rest resulted in a substantial reduction in fitness in the group as a whole, a reduction which was even larger than the one seen after 30 years of aging.  Given that there are only 5 participants, it is not surprising that the above changes were not statistically significant.  But when you look at the values for each individual participant (below), the results are even more striking.

The above figure would seem to suggest that 3 weeks of bed rest resulted in a consistent and rather substantial reduction in aerobic fitness in all 5 participants, while the impact of aging seems less consistent.  Again, there is no statistical significance, but it’s an interesting figure nonetheless.

Even moreso than with most papers, this study has a number of obvious limitations.  There were only 5 participants, the above results weren’t statistically significant, and the results were not controlled for other important factors.  So why post it here?  Frankly, because it’s kinda neat!  I love studies with rigorous design, but opportunistic studies like this can go a long way to filling in gaps in the narrative where more rigorous studies end off.  Not to mention that this was one of the first papers to suggest that sedentary time could have a strong influence on health.  Interestingly, the authors conclude that it is the lack of physical activity – as opposed to sedentary behaviour – which resulted in the apparent reduction in fitness following 3 weeks of bed rest.  Personally, I’m inclined to think that sedentary behaviour itself may have an independent impact on health, as I’ve discussed previously, but that’s a discussion for another day.

I know I’m reading more into this than the data itself might suggest.  So what do you think – is bed rest likely to be as bad or worse for fitness as 30 years of aging, or is this nothing more than over-interpretation of a null result?  I’d love to hear your thoughts.

Travis

ResearchBlogging.orgMcGuire DK, Levine BD, Williamson JW, Snell PG, Blomqvist CG, Saltin B, & Mitchell JH (2001). A 30-year follow-up of the Dallas Bedrest and Training Study: I. Effect of age on the cardiovascular response to exercise. Circulation, 104 (12), 1350-7 PMID: 11560849

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20 Responses to 30 Years of Aging vs 3 Weeks of Bed Rest – Which is Worse For Aerobic Fitness?

  1. Cindy Marsch says:

    With such a small group, I’d really like to know the individual “stories,” especially with the two guys at the top who started with high fitness and ended “flat” with their bedrest levels. I think the real question is what these gentlemen did during those thirty years. Did they keep up some level of aerobic fitness? And I’d love to see this study done again in two more decades, when they’re seventy instead of fifty.

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  2. Johan says:

    Looking at that second graph makes you wonder how much of the ravages of time that are normally attributed to aging is really the result of having lived an unhealthy lifestyle for a long time.

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  3. Linda Fair says:

    I would really like to have some qualitative information added to the study as well as a control group–i.e., 5 similar individuals who did not have the 3 weeks of bedrest, just the baseline and the follow-up. Perhaps the 3 weeks had some significant affect on their well-being? I’d love to know what, if anything, the 5 guys who had the 3 weeks bedrest thought about the results: Were they surprised? Did it affect their intention to avoid sedentary living? And I’d like to know how they felt, what they thought about the results of the 30-year study especially to what they attribute the decay of wellness?

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  4. BillC says:

    Wouldn’t we expect aerobic capacity to adjust to decreased demand from the respiratory system? The results here, then, are normal and demonstrate “health”, if the body’s ability to adapt is a sign of relative health. Also, to draw any conclusion about this research it seems we have to accept the assumption that bedrest and aging are both either apples or oranges and not one of each kind. And are there not several variables in the vo2 max measurement? Don’t we know that aging decreases vo2 max and that aerobic conditioning trains the body, by increasing its vo2 max, to perform better during periods of respiratory demand?

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    • Travis says:

      That’s an interesting point, but I’m not sure I agree with your definition of health. It’s important for the body to be able to adapt and respond in response to stress, but a reduction in aerobic fitness would actually mean that these men are less able to respond to physical stress.

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      • BillC says:

        vo2 max is an indicator of fitness but is fitness an indicator of health? Recent research has shown an increase in atherosclerosis in middle-aged distance runners as compared to non-runners. Other research indicates that elite cyclists have an increased risk for bone fracture. I assume that individuals in both of these groups have a pretty high vo2 max. And is the well-known addiction to so-called aerobic training a good thing overall?

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        • Travis says:

          Fitness does tend to be a pretty good indicator of health. Do you happen to have a link for that atherosclerosis paper? Would be very interested to read it.

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          • BillC says:

            Looking for it.

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          • BillC says:

            I googled “runners and increased atherosclerosis” and was presented with at least a half dozen links to credible research indicating the relationship. It seems to be a well-kept secret in the exercise sciences.

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        • Travis says:

          Hi Bill,

          I did the same google search as you, and see what you mean. There have been a couple recent studies suggesting that there is some aortic calcification among marathon runners, although that doesn’t necessarily mean that it’s causing atherosclerosis, or that these people would be healthier if they weren’t running.

          Here is part of the results section from one of those studies (http://www.medscape.com/viewarticle/579806_1):

          ‘The FRS in marathon runners was lower than in age-matched controls (7 vs. 11%, P < 0.0001). However, the CAC distribution was similar in marathon runners and age-matched controls (median CAC: 36 vs. 38, P = 0.36) and higher in marathon runners than in FRS-matched controls (median CAC: 36 vs. 12, P = 0.02). '

          So the overall Framingham Risk Score (an index of cardiovascular risk) was better in marathon runners than in age-matched controls. However, the amount of aortic calcification (which increases the risk of heart problems) was higher in the runners than in controls who were matched for overall Framingham Score. In other words, there may be something going on with aortic calcification related to marathon running, but that in general, total heart risk still seems to be reduced in these folks (which is what you'd expect).

          Here's a line from an editorial in the European Heart Journal discussing one of the recent studies (http://eurheartj.oxfordjournals.org/content/29/15/1800.full):

          'In the current report, weekly energy expenditure (probably corresponding to training mileage) was not associated with the amount of coronary artery calcium. However, the number of completed marathon races was. Is training for a marathon healthy—as previous data suggest and common belief holds—while the race itself is risky?'

          Another more recent study in MSSE looked at to see whether there was presence of atherosclerosis in marathon runners (there was), but they didn't compare that to age-matched controls. So all that tells us is that atherosclerosis occurs in runners, but not whether it's any better or worse than non-runners (http://journals.lww.com/acsm-msse/Abstract/2011/07000/Carotid_and_Peripheral_Atherosclerosis_in_Male.2.aspx)

          That was just my quick google search, so I may be missing things. I will try to add this to our list of things to discuss in the future, as it's an interesting topic. My guess is that running a marathon may be more problematic than simply doing aerobic exercise, since the marathon is a pretty big stress on the body.

          Travis

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        • Travis says:

          If I’m not mistaken, the blog in the below comment (sorry for posting back up here, but there wasn’t any room left down there) is just talking about bone health. I won’t dispute that extremely high levels of aerobic activity can be bad for bone health. But that’s completely separate from cardiovascular health.

          Also, I can’t argue that a marathon causes an acute increase in inflammation, which could be dangerous for at risk populations (as the other quote mentions). But that particular case study is just that – a case study. As with one of the studies I mentioned earlier, it doesn’t mean that running caused that individual’s heart problems.

          I think this quote from that case study sums up the current evidence nicely:

          “Vigorous physical exertion increases the short-term risk of sudden cardiac death in all people, yet simultaneously offers protection from this risk in those who exercise regularly”

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          • BillC says:

            The research shows that chronic long distance running is directly related to atherosclerosis and that chronic long distance cycling is directly related to osteopenia. Neither atherosclerosis nor osteopenia are associated with health. However I’m assuming that the subjects in the study had a pretty good vo2 max. Therefore, a high vo2 max is not necessarily an indicator of health.

            Chronic “aerobic” activity, such as running and cycling, conditions the body to adapt to non normal stresses. It has apparent benefits but it also has side effects that one may not want. Eventually one becomes habituated to running or cycling and you just don’t feel right unless you hit the pavement. It becomes addictive behavior – another contra-indication of health.

            just saying…

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  7. Peter J Engert MPT says:

    I find this research, even though it is on a small scale, interesting to note that most participants never regained their previous state of fitness after the bed rest. In fact, most of them remained at the low level while they were on bed rest.
    This supports timely mobility of patients in the hospital. As per this research, once the fitness level is diminished many patients may never regain their previous levels. It would be interesting to study this on a larger more statistically relevant basis. Thanks for the article.

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  8. Pat says:

    I agree that with such a small sample size, it would be important to know what these subjects did during those thirty years.

    Another interesting question: Does the influence of 3 weeks of bed rest will be the same in subjects aged 20 vs. 50 yrs ?

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