Fast Muscles, Happy Knees
It’s power, not strength that fights arthritis pain
Scientists at Tufts have determined that a lack of leg muscle power—the capability of the leg muscles to rapidly exert force—is a more accurate predictor of knee osteoarthritis pain than simple leg strength, a finding that could lead to better diagnosis and treatment of the often debilitating disease.
Led by Kieran F. Reid, an exercise physiologist at the Jean Mayer USDA Human Nutrition Research Center on Aging (HNRCA) at Tufts, the study, which appeared in the journal Arthritis and Rheumatology, examined the relationships among leg muscle strength, leg muscle power and perceived knee pain in people with osteoarthritis of the knee.
People with greater leg muscle power reported less knee pain and better quality of life.
Reid’s team gathered their data by measuring the leg muscle strength and power of 190 men and women, ages 41 to 90, with knee osteoarthritis. They assessed the strength and power mainly of participants’ quadriceps—the big muscles on the front of the thigh—but also that of other leg muscle groups, including those in the buttocks, hamstring and calf. Participants were asked to perform a set of leg exercises known as a double leg press extension on an exercise machine. Seated, the subject brings the knees to the chest and presses a weighted plate away from the body. The faster they can do the press, the better their muscle power.
The researchers found that people with greater leg muscle power reported less knee pain and better quality of life. Muscle strength, however, was linked to lower quality of life in some circumstances. However, Reid doesn’t believe those data are contradictory.
“We think power is a better way to evaluate the overall performance of skeletal muscle compared to strength,” he says.
“The key difference between training for building strength versus power is the speed at which the training is performed.”
Their findings bring some clarity to the scientific literature about the role of musculature in knee osteoarthritis. While some studies have found an association between more muscle strength and reduced pain—that is, stronger people felt better—others saw just the opposite. Measuring muscle power could eliminate the noise in the data.
“The key difference between training for building strength versus power is the speed at which the training is performed,” says Reid. “You can train on the same machines to develop strength and power, and with the same exercises—leg curl, leg extension, bicep curl, etc.—but to develop muscle power you have to perform the exercise very fast or as fast as you possibly can.”
Improving muscle power instead of just focusing on strength training might prove to be a more useful clinical goal, says Reid, who works in the Nutrition, Exercise Physiology and Sarcopenia Lab at the HNRCA.
“In previous studies, we’ve found that compared to muscle strength, muscle power is a stronger predictor of performance in tasks that are really important to older people and their physical independence, such as being able to get up out of a chair or climb a flight of stairs,” he says.
Focusing on building muscle power could prove critical to staving off both osteoarthritis and mobility problems in an aging population. While Reid’s team found that people with greater muscle power reported less pain and better quality of life, overall, the participants in the study were pretty frail. With an average age of around 60, this group’s muscle power was more in line with “mobility-limited older adults with a mean age of about 80 years,” the researchers wrote. Whether that’s a cause or an effect of their knee pain, Reid can’t say without further research.
But he says he wouldn’t hesitate to prescribe them exercise, especially based on his previous experience as a scientist on the Lifestyle Interventions and Independence for Elders study, led by Roger Fielding, a senior scientist and director of the HNRCA Nutrition, Exercise Physiology and Sarcopenia Laboratory. That study, which focused on sedentary men and women ages 70 to 89, “really showed for the first time that we can prevent or delay mobility loss in at-risk older persons using a structured exercise intervention,” says Reid.
“We’re big advocates of having older people exercise,” he notes, adding that more research is needed to determine the safest and most effective way to build muscle power in older people with knee osteoarthritis. “We know from the data that the older population tends to be the most sedentary, but they are also the most likely to benefit from exercise interventions,” he says.