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Aging: does the average decline as much as the extremes?

October 24th, 2011

My Jockology column in today’s Globe and Mail takes another look at aging and physical decline:

It’s the chicken-and-egg question of aging: Do we become less active as we get older because our bodies start to break down, or do our bodies start to break down because we allow ourselves to become less active?

For years, it was widely accepted that humans would start getting slower, weaker and more fragile starting in their 30s. But new studies on topics ranging from the cellular mechanisms of aging to the time-defying performances of masters athletes are forcing researchers to question this orthodoxy. It seems increasingly likely that the first signs of decline are more a function of lifestyle than DNA: If you keep using it, you’ll be well into middle age before you start losing it. [READ THE WHOLE ARTICLE...]

One of the studies discussed in the article is this analysis of the finishing times of 900,000 German marathoners and half-marathoners, published last year. The researchers argue that the rate of decline of mid-packers is a better way of judging “natural” aging processes compared to the outliers who set age-group world records. For fun, I plotted the average finishing times of the runners in the German study, and superimposed the curve that you’d get if they declined at the same rate as age-group records. It’s pretty clear that this group of midpackers does decline at a slower rate:

 

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  1. October 25th, 2011 at 01:22 | #1

    Very interesting post, but I am a bit confused by the graphs. The groups are labelled as decline ‘rate’ but the y axis looks like time in minutes for the marathon. And therefore based on the graph numbers the age group record runners seem slower than the average – which does not make sense. I presume the Y axis is mislabelled and it should be some ‘rate of decline’ number. Any thoughts?

  2. alex
    October 25th, 2011 at 01:48 | #2

    @Ward: Yeah, sorry, I didn’t explain the graphs very well. The “recreational runners” data is the raw data from the German study: it shows the real average times that they collected from marathon finishers in different age groups.

    The other line (labelled “Decline rate of age-group records”) is normalized to the 20-30 age group. In other words, it shows how performances would change if the percentage decline from age group to age group was the same as it is for age-group records.

    The point it’s trying to illustrate is that, for example, the 50-year-old record holder is farther behind the 40-year-old record holder than a 50-year-old mid-packer is behind a 40-year-old mid-packer.

  3. October 26th, 2011 at 07:56 | #3

    It seems like this study is mostly looking at recreational runners. It is hard to deny that there is a decline in absolute performance potential by the mid 30s in nearly every sport…not just running but also anaerobic sports. Pitchers in baseball train just as hard, but their fastball slowly losses its pop and begins to look like Jamie Moyer. You can see elite distance runners lose their speed, and then endurance.

    So, what should we make of these results. Training 3-4 times per week is not elite. While a 50 year old may not be able to run a 2:03 marathon, it seems like they will get the same results as a 30 year old with limited training. But if I trained them both hard, I doubt the results would stay the same. And at the top of each age group bracket you can see this.

    Another explanation of the results might be self selection. Lots of people run marathons in their 20s and 30s. Some are fit, some do it to lose weight, others just join the crowd. But people I know runninng marathons in their 50s and 60s typically continue at that age because they are good at it. The slower older folks self select themselves out of the samples and might skew the findings despite the large sample size. It would be interesting to see the number of runners per age group to see if this might be the case.

    Keep up the good work, I love reading your posts.

  4. Aaron
    October 26th, 2011 at 16:32 | #4

    I agree with a lot of what Martin says, but I’ll point out that 25% of the older runners had only been running for under five years. However, I’d be willing to guess that the pool of first-time marathon runners at age 20 is different from those running one at age 60. The older first timers I’ve met are usually someone who was various serious about something like biking who is looking for something new (although if I understand figure 4 in the study correctly, they found this wasn’t the case for about half of the older runners). But the fact that the 60+ crowd is the vast minority of the runners (3.7% of the male subgroup and 1.7% of the female subgroup) speaks a lot to this self-selection.

    It seems like this study is working with very muddy data. Marathon running has been going on for over a century, and given how obsessive even non-elite runners are, I’m sure there are enough training logs to do a non-cross-sectional study that looks at age related decline.

  5. alex
    October 26th, 2011 at 17:47 | #5

    @Martin and @Aaron: Thanks for the comments. And I definitely agree that there are significant issues with selection bias in the study! By no means would I argue that the German study truly uncovers the real rate of “physiological” decline.

    That being said, I did find the study interesting, for the simple reason that, if you’d described the methodology to me and asked what results I expected to see, I would have predicted a somewhat steeper decline. Whatever the complex mix of factors at play, it’s surprising (and a bit encouraging!) to me to see how little difference there is between the average 55-year-old and the average 35-year-old at road races.

  6. alex
    October 26th, 2011 at 17:50 | #6

    @Aaron: “Marathon running has been going on for over a century, and given how obsessive even non-elite runners are, I’m sure there are enough training logs to do a non-cross-sectional study that looks at age related decline.”

    Just wanted to add: there are indeed some studies (e.g. this one) that compare cross-sectional and longitudinal data, and find that the rate of decline is slowed in the longitudinal data from lifelong athletes. But these still represent a rather narrow and self-selected slice of the population.

  1. October 25th, 2011 at 14:37 | #1