I WAS two-thirds of the way across one of the longest bridges in the US, near the front of a pack of 1500 runners. The 10-kilometre race, called the Great Columbia Crossing, was reaching its climax, where the bridge humps up in an 80-metre-high span across the shipping channel before plummeting to the finishing line among the fishing docks of Astoria, Oregon.
I had been running races for more than 20 years, and I knew that on the eve of my 48th birthday, my body wasn't what it once was. According to World Masters Athletics, an advocacy group for older athletes, the passing years should have added about 311/2 minutes to my lifetime best time-37 minutes 44 seconds, achieved when I was 30 (see Diagram). So I had no delusions of setting a new personal best. Instead, my secret goal was to beat the age-adjusted time, if only by the smallest margin.
At first glance, it's obvious why we slow down with age: our bodies are wearing out. But when I dug a little deeper, I found that researchers are only beginning to work out exactly what goes wrong, how much decay is inevitable, and how much can be averted with the right sort of exercise. But the training strategies I learned to follow in preparing for my race can help almost anyone-from weekend athletes to senior citizens-hold back the creeping advance of age and stay younger longer.
Much of the research on declining athletic performance focuses on the body's maximum oxygen consumption, or VO2max. This is a classic measure of aerobic conditioning, reflecting how well the lungs take in oxygen, how much blood the heart can pump, and how hard the muscles work during exercise. It's measured by running on a treadmill up an ever-steepening grade. The amount of oxygen you're consuming at the point where you're ready to collapse is your VO2max. For sedentary people, VO2max typically declines by about 10 per cent per decade after 30 years of age. For athletes who keep in training, by contrast, the decline is about half that.
The conventional wisdom is that the heart is to blame for much of the decline, since there's a steady fall with age in the number of receptors on the heart muscle that listen to the nervous system's signals telling it how fast it should beat. As the heart becomes deaf to messages urging it to work harder, its maximum rate drops by about one beat per minute each year-a decline that everyone assumed would translate into less oxygen delivered to the muscles during times of peak workload, and hence a lower VO2max.
But late last year, this comfortable theory was set on its ear. In the 1960s, Darren McGuire and Benjamin Levine from the University of Texas Southwestern Medical Center and Presbyterian Hospital in Dallas had studied the physical fitness of five healthy men in their early 20s before and after three weeks of voluntary bed rest. In the late 1990s, McGuire and Levine revisited the same men, then aged 50 or 51.
Never before had scientists studied the effect of age on non-athletes whose fitness had been so thoroughly tested when they were young. The researchers compared old and new X-ray measurements of the volume of blood pumped with each heartbeat. They already knew that this volume increases with age, as the heart enlarges to force blood through age-stiffened arteries. But to the surprise of cardiologists, McGuire and Levine found that this increase in volume was more than enough to offset the decline in maximum heart rate. A 50-year-old's heart might not beat as fast as it once did, but it can pump at least as much blood per minute.
In other words, VO2max declines with age not because the heart grows less able to deliver oxygen, but because the muscles somehow become less able to use it. As yet, exercise physiologists can't explain why this happens. McGuire and Levine speculate that older muscles may have fewer capillaries supplying them with blood. Perhaps they are less able to call for extra blood when they need it, or their cells have fewer mitochondria. Or maybe the arteries supplying the muscles get clogged up with age.
But whatever the cause, the study shows that sedentary middle-aged people can vastly improve their VO2max simply by becoming more active. When the 50-year-old men began exercise programmes that gradually built up to between three and five hours per week, their average aerobic fitness improved so much that within six months it returned to what it was when they were 20. "We reversed 30 years of ageing with six months of training," says Levine.
Curiously, the VO2max of one of the men-the only one who chose to exercise by riding a bicycle instead of jogging or walking-showed no improvement. The scientists suggest that this may have been because his VO2max was measured on a treadmill, not a bicycle. This shouldn't matter if the heart's pumping ability is the main reason VO2max tails off with age. But if the decline in VO2max stems mostly from the muscles, this finding may be critical. Training may improve only the aerobic capacity of the muscles being trained-and cycling and running use different muscles.
Elite athletes have long known this. Coaches preach "specificity" in training: to excel, athletes must focus the bulk of their work on the muscles involved in their sport. McGuire and Levine's finding may have something to teach the rest of us too. If your goal is to maintain whole-body fitness as you age, you should vary your exercise to distribute the benefits more evenly.
McGuire and Levine's 50-year-olds could have tried one other trick to boost their aerobic fitness well beyond what they could do as untrained 20-year-olds. They could include "wind sprints" or other forms of high-intensity "interval" training. A series of moderate-length, intense "repeats" that leave you gasping for breath can kick your VO2max up an extra notch, even if you're past your athletic prime. Prior to the Great Columbia Crossing, I'd been doing exactly this, with gruelling workouts in which I'd run hard for 800 to 1200 metres, rest, then do it again.
Dr Richard Stein, a professor of clinical medicine at Weill Medical College of Cornell Universiy in New York City, agrees that in the absence of coronary artery disease, arthritis, dangerously high blood pressure, or some other major ailment, putting yourself on an increasingly regimented training programme is a good formula for staving off some of the effects of age. By turning up their exercise levels slightly each year, Stein suggests, people who were in average shape at 30 might be able, say, to move into the top 40 per cent of 40-year-olds and the top 30 per cent of 50-year-olds.
The more active your youth, though, the less room there will be for improvement-a particular problem for me since I trained hard even in my 20s. Some endurance athletes may even burn out completely (see "Going too far too fast"). "It would be nice to say you would be, at 50, everything you were at 20, but there is a reality to this," says Stein. "But if you're not at the level of an elite athlete when you begin, you can at least ameliorate the decline."
A superb case in point is John Keston, a retired Royal Shakespeare Company actor and opera singer who started out relatively inactive and only began running at 55, initially to manage his high blood pressure. Fourteen years later, he became the oldest man ever to break the three-hour barrier in a marathon-a feat he came within a minute of repeating at 71. Now aged 77 and living in Oregon, he's still far fitter than he was when he was my age, and he can race me to a dead heat despite a 29-year age difference. Even Keston, though, is slowing down. His best marathon in 2001 was a world record for his age, but it was well shy of the bests he'd achieved in his 60s and early 70s.
Another way to keep ahead of the ageing process is to take up weightlifting. In my youth I shunned weights, but in preparation for the Great Columbia Crossing, I pumped iron every third day. Anyone-even a 90-year-old-can benefit from a strength-training programme of this sort. But to get the biggest pay-off you need to push your limits, no matter what your age, says Scott Trappe, who directs the Human Performance Laboratory at Ball State University in Muncie, Indiana. The standard recipe: find a weight that gives you a good "burn" through three sets of 10 repetitions each, and you'll build muscle strength nicely.
But there's bad news for couch potatoes: unlike your aerobic capacity, your muscles can't easily recover their youthful form after decades of inactivity. Trappe and his team have painstakingly teased out individual muscle cells from biopsies, anchoring the cells to instruments that monitor what happens when they are chemically stimulated to contract. This allows the researchers to determine precisely what type of cells are strengthened by training, and they've found an intriguing difference between young muscles and old ones.
There are two basic types of muscle fibres, commonly called fast-twitch and slow-twitch based on the speed at which they contract. Fast-twitch fibres provide sudden, brief bursts of power, useful for sprinting or weightlifting. Slow-twitch fibres contract more slowly but have more endurance. People vary in how much of each they're born with, and athletes tend to gravitate towards sports that favour their particular mix. Sprinters tend to have muscles that are three-quarters fast-twitch; endurance athletes can have as much as 90 per cent slow-twitch.
Trappe's team has examined athletes of all ages, as well as non-athletes up to their mid-80s. The researchers have discovered that as people age, they lose fast-twitch fibres more quickly than they lose slow-twitch ones. Presumably, Trappe says, it's a use-it-or-lose-it phenomenon. When people in their 70s or 80s stop doing the high-intensity activities that call for fast-twitch fibres, the unneeded cells shrink and eventually die. Slow-twitch fibres atrophy more slowly because they're called on for daily activities as simple as maintaining your posture.
When young people take up weightlifting, they build mostly fast-twitch fibres-not surprising, given the nature of the activity. Old people, whose fast-twitch fibres have mostly withered, still bulk up by about the same percentage, but Trappe's team has found that they do so by adding more slow-twitch fibres rather than replenishing their fast-twitch. They gain muscle mass and strength, but not the type of power that comes from fast-twitch fibres.
This may partly be because they begin their exercise programmes with reduced supplies of fast-twitch. But Trappe believes that something hinders the growth of the fast-twitch fibres that do remain. Muscles grow with exercise, he notes, because some signal turns on genes that tell muscle cells to become larger and more numerous. He is now trying to discover why ageing slow-twitch cells get the message while fast-twitch ones apparently do not. Answering this may help us to develop strength-training programmes that boost both types of fibre.
All this talk about maintaining aerobic conditioning and retaining muscle mass is well and good, but there's another problem that often throws a spanner in the works. For reasons that aren't well understood, the body heals more slowly with age, which means it takes more time to recover from workouts. Relatively young athletes can compensate for this fairly easily. When Carlos Lopes of Portugal won the 1984 Olympic marathon at 37, then broke the world record at 38, he was able to adjust for the effects of age by increasing the number of easy days that he took between intense workouts. A decade older, I found I had to cut back still further to avoid injury, never running more than five days per week, and never doing even moderately hard training runs on consecutive days. Keston, in his late 70s, carries this a step farther, taking two days full rest after each training run.
Luckily for me as I raced in the Great Columbia Crossing, all athletes of my age face the same obstacles. My advantage, I hoped, was that I had learned more than most people about how to train for both VO2max and strength. It worked even better than I expected, and I crossed the finishing line well ahead of schedule, logging 40 minutes and 50 seconds. Later, when I plugged that into the age-related performance charts, I found that it was equivalent to a youthful 37 minutes 16 seconds. I'd achieved my goal with nearly half a minute to spare, and it didn't bother me that this new "best" was several minutes slower, by the clock, than my previous time. I had beaten age, and that was all that mattered.
Age isn't the only thing that causes athletes to slow down. South African exercise physiologist Tim Noakes believes that endurance athletes simply burn out. Marathon careers last about 20 years, says Noakes. "My interpretation is that, physically, that's about how much heavy training a human can do."
Living in a country where "ultramarathon" running is a national obsession (the 90-kilometre Comrades Marathon draws as many as 15,000 runners), Noakes is well positioned to encounter burnt-out athletes-people who, after 16 or 18 ultramarathons, suddenly find that they can no longer keep up with their training partners or do workouts they once took for granted. Noakes's laboratory at the University of Cape Town Medical School has conducted extensive studies on about 30 such men, monitoring them as they work out, taking muscle biopsies, and even testing their DNA.
In findings soon to be published, Noakes focuses on "satellite cells", whose function is to grow replacements for damaged muscle cells. These satellites, he says, seem able to undergo only a limited number of repair cycles before accumulated DNA damage impedes this process.
Noakes cautions that his results do not apply to people who exercise only moderately, say 3 to 5 hours a week. Problems set in, he believes, for people who take part in races longer than 30 kilometres. "My hunch is that whenever you have marked muscle soreness that lasts more than a few days, there is probably damage that's not reversible in the long term," he says.