Exercise and aging: Growing old gracefully, with speed!
Yesterday we began a series on exercise and aging by looking at the world records across the age categories. To remind you, here's the graph minus the notes from yesterday:
I've indicated the records for 30 years, 50 years and 72 years, just to illustrate the main point of today's post. You can work out who holds the 30-year old record if you want (hint: He is one of only four people to break his own world record, and he ran for a country not of his birth). The 50-year old is Titus Mamabolo (a South African - our only record holder these days), and the 72-year old is Ed Whitlock of yesterday's post.
But the point that I alluded to yesterday is that there is a flaw in using this graph (or the relationship) to project what your own time will be at age Y based on your time aged X.
That's because the graph you see above is made up of perhaps 50 different runners, and each one has an entirely different trend in performance over the years. The individual running 2:05:38 will NOT be running 2:19:29 at 50, and will NOT run 2:59 at the age of 72. We know this because it hasn't happened on a single occasion in all the age-group records that one individual holds records more than 9 years apart. Ed Whitlock, who we introduced yesterday, and will feature again the future, is the holder of the most records - he owns 8 age-records, all in a batch.
A window of performance? Depends on the performance...
This seems to suggest that individuals have a narrow "window" during which they are able to excel. Bear in mind that "excel" in this case means running faster than any person in history! That's a tough bar to set, so I must make the allowance that the "window" becomes much longer when you start to lower the performance level slightly. That is, someone who is running at say 80% of the world record pace can probably much more accurately work out how their performances should change over time (which is why those calculators that predict your age-equivalent times do have some merit)
Of course, people tend to over-value those equations and formulas that work out what your time at the age of say 60 would be equivalent to if you were 30. While interesting, such predictions can't really be used as "instructive" or to judge your current performance, because you're on your own journey, and the changes over time can't really be accounted for unless you do a massive study that looks at say 500 individuals over the course of 60 years and plots the average decay in performance (and, to the best of my knowledge, that hasn't been done).
The reasons for the decline - age physiology
So now we get to the reasons for the decline. And this is relatively well-known physiology, which I promised yesterday that I'd avoid spending too much time on. However, it's important to understand as we move forward, because the next step will be too look at "Chronological Age vs. Running Age", and so we need to understand Chronological age.
So what can you expect as you get older? (That feels very morbid as I type it..., sorry)
Aging affects numerous physiological systems, including the neuromuscular, hormonal, respiratory, cardiovascular and metabolic systems.
Lean muscle mass and age
Perhaps the most widely known and significant changes that occur with aging are those that affect the muscle, and happen in part because the levels of hormones like testosterone and growth hormone fall over the years. Testosterone is the one everyone knows about because dopers use it so often, and as any body-builder will tell you, is anabolic (as opposed to catabolic), because it builds up tissues in response to stress, and is responsible for muscle growth and development after training.
Testosterone levels peak during adolescence and early adulthood, but somewhere between 30 and 40 years of age, begin to decline progressively. As a result, lean muscle mass declines by as much as 30% between 25 (when peak muscle mass occurs) and 70 years of age. This reduction involves decreases in the total number of muscle fibers and a decrease in the size of the fibers. At the same time, oxidative damage causes further reductions in muscle mass, as does a decline in the number of motor neurons that provide neural “nourishment” to the muscle fibers.
The net effect of the reduction in muscle mass is a loss of muscle strength – as much as 2% per year, so that by the age of 70, strength is reduced by up to 40%, though this depends on the individual and also their activity levels. Training helps prevent these reductions, which is good news, and is the part of the equation that you can control.
One of the more obvious, and upsetting consequences of this change is that your metabolic rate slows down, and so you start to gain weight (fat mass, that is). The common misperception that "muscle turns into fat" is actually the storage of fat that is partly caused by a loss of muscle thanks to aging. It's not that muscle is converted to fat, but rather that fat now tends to be deposited much more easily. If you don't adjust your diet, "middle age spread" is the result!
Injury and adaptation
One of the more frustrating aspects of aging (and the reason you've probably been the butt of some jokes from friends) is that your ability to recover from training is reduced. Pretty much all "moving parts" don't quite recover from sessions the day before, and your body’s ability to adapt to the stress of training is also reduced. You can no longer repair damage by laying down stronger muscle fibers in response to training. One of the big benefits of taking testosterone is that it aids recovery, allowing harder training. Aging is effectively "reverse doping", since testosterone is reduced, and training can't be done to the same level as before. One of the first things people will notice is that they wake up stiff and commonly jokingly say "I must be getting old". Exactly!
Other hormonal changes further contribute to this adaptation barrier – the production of growth hormone decreases steadily from the age of 10, just after puberty, which has much the same effect as the fall in testosterone, as well as some other effects on metabolism. Growth hormone has even been called the “anti-aging” hormone, a popular choice among the Hollywood elite to retain their celebrity looks! We'll return to this hormone again in the future...(thanks to Peter for his input on that one)
Other aging effects
There is also a decrease in the number of capillaries to each muscle fiber, which means that valuable energy and oxygen delivery to muscles is compromised. Stroke volume (the amount pumped per contraction) and heart rate also fall over time, meaning less blood can be pumped to the body as cardiac output falls. Respiratory muscles get weaker, and the resistance in the airways rises, which makes breathing harder work. The ability to get valuable oxygen out of the air into the blood and to the muscles is reduced, not a great outcome for a marathon runners! It doesn't take a degree in exercise physiology to appreciate how these changes in the heart and lungs would make running or any other endurance activity much more difficult.
Inside the muscle, proteins that are important to assist with metabolism are not produced in the same quantities – you therefore become less effective at producing ATP to power muscle contraction. The muscle’s capacity to store and release energy changes with age – less glucose and glycogen can be stored, and the muscle becomes less sensitive to hormones that normally drive metabolism, like adrenaline.
Changes in women - even more pronounced
In women, hormonal changes have even more dramatic effects – menopause and the associated hormonal changes are responsible for many effects, perhaps the most relevant for running being a decrease in bone mineral density that predisposes women to the development of osteopenia, which is a precursor to the more serious osteoporosis, where the risk of fractures is greatly increased.
Here, the excellent news is that running (and other exercise), because it is a weight-bearing exercise, is one of the most effective means of preventing osteoporosis, because it helps elevate the bone mineral density at a young age so that the inevitable age-induced decline does not have potentially disastrous consequences.
The same goes for all the other changes - the body ages, this is as inevitable as death and taxes (as the saying goes). However, regular exercise slows down the rate of decline in many of these systems, or at least reduces the impact of the change. The result is that regardless of what you've read in this post, and the fact that you may be bemoaning lost youth (don't worry, I am too!), if you continue to exercise now, then you'll reap the benefits, in spite of your natural battle against father time!
Chronological age vs running age
Well done if you've managed to read this far. This was a "textbook" physiology post, not my favourite kind, but hopefully I've skimmed through all the important systems and how the years affect them. If you're a scholar or student who just happens to be doing an assignment on this topic, then you're in luck (Please feel free to donate to us through our PayPal link! And don't forget to reference everything you say!)
However, this is all a precursor to the more juicy and exciting discussion to come, probably next week. That's when we'll start looking at the impact of many years of running as compared to many years of living. There is evidence that running age is just as important as chronological age in determining running performance, and that the two interact to properly explain what you will have experienced. And the notion of a "window" of opportunity seems to be borne out.
So let's tackle that next week, when we're all three days older. Hope this was instructive and not too morbid!
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Thursday, February 12, 2009
Exercise and aging: Growing old gracefully, with speed!