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New research conducted by the University of Wisconsin - La Crosse Department of Physical Therapy calls into question the conventional wisdom that non-impact cardio machines, such as adaptive motion trainers (AMTs), apply minimum stress to the joints. The study shows that some cross trainers, particularly ones that move in an elliptical-like pattern, may still impose high stresses on the knee. The research was funded by the
Cybex Research Institute (CRI), research division of Cybex International Inc. (NASDAQ: CYBI).
“What we’re learning is that shock is not the only relevant factor in reducing knee stress,” said Dr. Paul Juris, executive director of CRI. “Even in low or non-impact motion, compression at the patellofemoral joint – just under the kneecap – can be significant. With millions of people suffering from knee pain, this research comes at a critical time.”
Anterior knee pain is the most common complaint among physically active adults and children and accounts for 62% of all knee injuries. 1
Patellofemoral Pain Syndrome (PFPS) accounts for 57% of all knee problems in runners. 2.5 million runners are diagnosed with PFPS in a calendar year. 2
As the problem persists, people are migrating to non-impact forms of exercise like ellipticals and AMTs assuming that it's a safe alternative. However this new research shows that non-impact cross trainers are not stress-free, and that patellofemoral stress occurs at levels significantly greater on some devices than on others.
In the University of Wisconsin study, 16 subjects exercised at 75% of their age-predicted maximum heart rate on the Cybex Arc Trainer and Precor AMT cross trainer, at a constant pace of 100 steps per minute. An instrumented foot plate measured pedal reaction forces and an eight-camera infrared motion capture system measured pedal position, body position, and joint angles. Based on this information, peak patellofemoral joint forces (PFJFs), measured in Newtons per kilogram (N/kg), were calculated to be 141 percent greater on the AMT compared to the Arc Trainer. While the values for the AMT (19 N/kg) were comparable to that of stair climbing (21 N/kg) and lunging (19 N/kg), the Arc Trainer (8 N/kg) was more comparable to walking (9 N/kg). The Arc Trainer allowed users to maintain a high-level workout with PFJFs less than half that of the AMT.