One of the most
entrenched beliefs about running, at least among nonrunners, is that it
causes arthritis and ruins knees. But a nifty new study finds that this
idea is a myth and distance running is unlikely to contribute to the
development of arthritis, precisely and paradoxically because it
involves so much running.
It’s easy to
understand, of course, why running is thought to harm the knee joint,
since with every stride, ballistic forces move through a runner’s knee.
Common sense would suggest that repeatedly applying such loads to a
joint should eventually degrade its protective cartilage, leading to
arthritis.
But many of the
available, long-term studies of runners show that, as long as knees are
healthy to start with, running does not substantially increase the risk
of developing arthritis, even if someone jogs into middle age and
beyond. An impressively large cross-sectional study of almost 75,000 runners
published in July, for instance, found “no evidence that running
increases the risk of osteoarthritis, including participation in
marathons.” The runners in the study, in fact, had less overall risk of
developing arthritis than people who were less active.
But how running can combine high impacts with a low risk for arthritis has been mysterious. So for a new study
helpfully entitled, “Why Don’t Most Runners Get Knee Osteoarthritis?”
researchers at Queen’s University in Kingston, Ontario, and other
institutions looked more closely at what happens, biomechanically, when
we run and how those actions compare with walking.
Walking is widely
considered a low-impact activity, unlikely to contribute much to the
onset or progression of knee arthritis. Many physicians recommend
walking for their older patients, in order to mitigate weight gain and
stave off creaky knees.
But before the new
study, which was published last week in Medicine & Science in Sports
& Exercise, scientists had not directly compared the loads applied
to people’s knees during running and walking over a given distance.
To do so now, the
researchers first recruited 14 healthy adult recreational runners, half
of them women, with no history of knee problems. They then taped
reflective markers to the volunteers’ arms and legs for motion capture
purposes, and asked them to remove their shoes and walk five times at a
comfortable pace along a runway approximately 50 feet long. The
volunteers likewise ran along the same course five times at about their
usual training pace.
The runway was
equipped with specialized motion-capture cameras and pads that measured
the forces generated when each volunteer struck the ground.
The researchers used
the data gathered from the runway to determine how much force the men
and women created while walking and running, as well as how often that
force occurred and for how long.
It turned out, to no
one’s surprise, that running produced pounding. In general, the
volunteers hit the ground with about eight times their body weight while
running, which was about three times as much force as during walking.
But they struck the
ground less often while running, for the simple reason that their
strides were longer. As a result, they required fewer steps to cover the
same distance when running versus walking.
The runners also
experienced any pounding for a shorter period of time than when they
walked, because their foot was in contact with the ground more briefly
with each stride.
The net result of
these differences, the researchers found, was that the amount of force
moving through a volunteer’s knees over any given distance was
equivalent, whether they ran or walked. A runner generated more pounding
with each stride, but took fewer strides than a walker, so over the
course of, say, a mile, the overall load on the knees was about the
same.
This finding provides a
persuasive biomechanical explanation for why so few runners develop
knee arthritis, said Ross Miller, now an assistant professor of
kinesiology at the University of Maryland, who led the study. Measured
over a particular distance, “running and walking are essentially
indistinguishable,” in terms of the wear and tear they may inflict on
knees.
In fact, Dr. Miller said, the study’s results intimate that running potentially could be beneficial against arthritis.
“There’s some
evidence” from earlier studies “that cartilage likes cyclical loading,”
he said, meaning activity in which force is applied to the joint,
removed and then applied again. In animal studies, such cyclical loading
prompts cartilage cells to divide and replenish the tissue, he said,
while noncyclical loading, or the continued application of force, with
little on-and-off pulsation, can overload the cartilage, and cause more
cells to die than are replaced.
“But that’s
speculation,” Dr. Miller said. His study was not designed to examine
whether running could actually prevent arthritis but only why it does
not more frequently cause it.
The results also are
not an endorsement of running for knee health, he said. Runners
frequently succumb to knee injuries unrelated to arthritis, he said, and
his study does not address or explain that situation. One such ailment
is patellofemoral pain syndrome, which is often called “runner’s knee.”
But for those of us
who are — or hope to be — still hitting the pavement and trails in our
twilight years, the results are soothing. “It does seem to be a myth,”
Dr. Miller said, that our knees necessarily will wear out if we continue
to run.
