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 3 different time points: baseline, following 3 weeks of bed rest, and following 8 weeks of physical training. In 1996 these same 5 men were assessed for a fourth time, 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. Again, there is no statistical significance, but it’s an interesting figure nonetheless, especially given the mounting evidence of links between sedentary behaviour and health risk.
Even more so 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 they 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 itself – which resulted in the apparent reduction in fitness following 3 weeks of bed rest. Personally, I’m inclined to think that sedentary behaviour 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.
McGuire 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