The world's most common joint disease, osteoarthritis
(OA) is a major cause of disability among adults over the
age of 50. Whether physical activity is beneficial or detrimental
to weight-bearing joints, knees in particular, has been open
to debate. Some studies implicate physical activity in provoking
knee OA, while others suggest that physical activity may actually
protect the knee joint from the disease.
Confounding the matter is the fact that knee injury is a known
risk factor for knee OA. Then, there's the unclear role of osteophytes
in knee OA progression, compounded by the limitations of radiographs
for monitoring small yet significant changes in joint structure.
For a clearer picture of the impact of physical activity
on the knee joint, a team of researchers in Australia turned
to magnetic resonance imaging (MRI). This highly accurate
high-tech tool makes it possible to directly visualize joint
structures, detect early and pre-disease states of OA, and
assess the influence of potential risk factors. Taking advantage
of this novel methodology, the researchers studied the effect
of physical activity, in various degrees of intensity, frequency,
and duration, on knee structures in a total of 257 healthy
adults between the ages of 50 and 79, with no history of knee
injury or OA. Their findings, presented in Arthritis Care
& Research suggest that exercise that is good for the
heart is also good for the knee.
Recruited from an established community-based research population,
the Melbourne Collaborative Cohort Study, subjects all underwent
MRI exams on the tibia bone and tibiofemoral joint of their
dominant knee--the one on the leg they first step forward
when walking. MRI was used to assess cartilage defects and
bone marrow lesions, as well as measure cartilage volume,
an indicator of cartilage health and strength.
Loss of knee cartilage is linked to worsening knee symptoms
in OA sufferers. Subjects also answered specific questions
regarding their exercise and walking habits, as well as routine
activity at home and at work, to determine their level of
physical activity in both the 6 months and 7 days prior to
the study. To create a baseline for each subject, past information
on weight, height, body mass index, and physical activity,
from questionnaires completed between 1990 and 1994, was obtained.
Then, the team performed a series of analyses and comparisons.
Among the notable findings, both baseline and current vigorous
physical activity-- exercise that gets the heart pumping and
the body sweating--were associated with an increase in tibial
cartilage volume, free from cartilage defects. What's more,
tibial cartilage volume increased with frequency and duration
of vigorous activity. Recent weight-bearing exercise was also
linked to increased tibial cartilage volume and reduced cartilage
defects. Finally, moderate physical activity, including regular
walking, was associated with a lower incidence of bone marrow
"This is the first study to demonstrate a potentially
beneficial effect of walking on the reduction in the risk
of bone marrow lesions in the knee," notes the study's
leading author, Dr. Flavia M. Cicuttini. "Bone marrow
lesions have been associated with pain and radiograph-defined
progression of osteoarthritis, type II collagen degradation,
and loss of cartilage volume."
Demonstrating a protective effect of past and current vigorous
physical activity on knee cartilage in healthy adults, this
study strongly supports the benefits of exercise for older
individuals at risk for OA. Though both the intensity and
duration of physical activity had a significant positive impact
on cartilage, the ideal amount of physical activity for joint
health remains unclear. "Our data suggest that at least
20 minutes once per week of activity sufficient to result
in sweating or some shortness of breath might be adequate.
This is similar to, if not somewhat less than, the recommendations
for cardiovascular health," Dr. Cicuttini observes.