The Impact of Running

Posted on April 28, 2008 by

The Impact of Running

Can you have too much of a good thing?


By Martica Heaner, M.A., M.Ed., for MSN Health & Fitness


Q: I love running. I usually run about 7 to 8 mph for 90 minutes on the treadmill, five days a week. My distances can vary, though I typically run about 13 miles and I always try to burn at least 1,000 calories, according to the treadmill.
Is too much running bad for my heart and lungs? I’m 17 years old, 5-feet-2 and weigh 129 pounds.
A: You sound like a natural born runner. You run fast and long, and the fact that you can spend hours every week slogging it out on a treadmill—a task that many people would find extremely tedious—suggests that you are seriously hooked.

Are you running too much? Well, that’s debatable.
On one hand, the human animal is designed to be more active than the average couch potato. Studies of non-modern cultures find that people move continuously for hours as they go through the tasks of daily living.
On the other hand, the way that the body metabolizes energy suggests that it’s hardwired to function efficiently for low-intensity movement, such as walking briskly, for long periods. But to move at vigorous intensities, such as running fast, the body is geared towards doing it in short spurts.

That’s because high-intensity action is fueled by a process that uses quick-energy molecules and carbs, which are only available for up to a couple of minutes at a time. In other words, this fast-acting fuel is in short supply and runs out. That’s what happens when “hitting the wall” in a marathon or gasping for breath after sprinting to first base.
But longer-lasting action relies on fat for fuel. Even thin people have millions of fat cells and can be fueled for hours and hours on this endless energy source as long as the physical intensity is low to moderate.
We humans are capable of improving our capacity to run for long distances at high intensities, like in marathons. But physiologically speaking, we perform optimally—there is less chronic wear and tear on the body—when the high-intensity work is intermittent and followed by lower-intensity recovery periods, such as when playing basketball or tennis.
So just because you have the ability to train your body to tackle extreme physical challenges, that doesn’t mean you should. Here’s why.

It’s Not Just Joints That Take a Beating
Many people assume that it’s just joints that take a pounding during prolonged activities like running. In fact, you can avoid impact injuries if you train smart (build up gradually) on good surfaces with good shoes (and it helps to start with good, strong body parts). But what goes on in other areas of your body may be of greater concern.

Within a relatively new field of study known as exercise immunology, it’s well-established that chronic overtraining—or even one long, extremely-hard workout—is associated with a greater susceptibility to cold and flu. David Nieman, a professor of exercise physiology at Appalachian State University in Boone, N.C., found that runners who finished the Los Angeles marathon were six times more likely to get sick than those not running.

There appears to be a spectrum: Too little exercise is associated with poor health. Regular exercise, even at very low intensities, improves health. For example, people who walk at a moderate pace for 35 to 45 minutes a day, five days a week, experience half the sick days as non-exercisers. But too much unrelenting exercise for long periods (90 minutes or more, according to some research) may hurt health—even though the person who can handle this workload is, on the surface, a picture of fitness and health.

What Happens Inside
Extreme exercise increases stress hormones like epinephrine, norepinephrine and cortisol. These hormones help the body shift to a more efficient fat-burning metabolism to preserve fuel in the muscles known as glycogen (or carbs) and they help open blood vessels to deliver oxygen to muscles.

But if a person doesn’t dial down the intensity for even short periods, stress overload can occur. This can trigger an increase in white blood cells that eat bacteria, viruses and even cancer cells. After the intense exercise, these immune cells may plummet. It’s theorized that any viruses or bacteria present at this stage when the immune system’s weak could multiply. That is, the exerciser gets sick.

Still, this and other cellular changes that occur after relentless training appear to be short term. Within days, the immune system will return to normal. Additionally, Nieman’s research has shown that endurance athletes who consume enough carbs during a long endurance event can lessen the negative immune response.

What worries some medical experts more is that intense exercise increases the production of free radicals. Free radicals are out-of-control cells that can disrupt surrounding cells. These “pro-oxidants” are normal and necessary, and the body has natural defenses that help keep them under control. But when this system gets out of balance, DNA damage may occur, possibly waking dormant cancer cells.

Nieman and other researchers have expressed concern about a potential increased cancer risk in elite athletes. But so far, this is just academic speculation. The National Runners’ Health Study has tracked the disease and death rates of more than 115,000 runners and 45,000 walkers. The study has found no increased rate of total cancers in those running even up to 100 miles per week. (Interestingly, except for being leaner, those who run more than 40 miles per week do not show further health benefits, such as better cholesterol and lower blood pressure, than those who run up to 40 miles per week. This suggests that past a certain point “more” is not always better.)

So, should you cut back on your running? If you are eating enough to fuel your workouts, getting enough sleep, and not experiencing aches and pains or even mental burnout, then probably not. These extreme stresses from exercise are unlikely to occur after a three or six or even nine-mile run or similar workout.

But you should avoid training to exhaustion, and don’t be reluctant to slow down or take breaks. In any tough workout, weave in easy recovery bouts, even if these breaks just last seconds. One method of marathon running that incorporates this approach is the intermittent run-walk technique developed by former marathoner Jeff Galloway.
Also, vary the type of exercise you do to build all-over fitness. Read my book Cross-training for Dummies for ideas. You are young, so chances are it could be years before any excess exercise takes its toll. Remember that you probably want to keep running into your 90s. So preserve your body for the duration: Stay strong and sweat smart.