The effects of 16 months of angle-specific isometric strengthening exercises in midrange on torque of the knee extensor muscles in osteoarthritis of the knee: a case study.

Although often advocated for arthritis rehabilitation, several studies conducted on healthy subjects have demonstrated conflicting results as to whether isometric strengthening exercises performed at one joint angle can result in strength gains at other angles. The objective of this study was to determine whether midrange strength training of the quadriceps surrounding an osteoarthritic knee would increase strength in this part of the range of motion as well at other knee angles. The midrange position was chosen because the subject, a 57-year-old female with a 2-year history of moderately severe osteoarthritis of the left knee, had greatest weakness in this position. The training occurred three times per week for 16 months using a resistance training program of three sets of two maximal isometric contractions at a knee angle of 60 degrees. The dependent variable of maximal isometric knee extensor torque was recorded on an isokinetic dynamometer at knee angles of 90, 60, and 30 degrees at 6 weeks, 1 year, and 16 months. These data demonstrated a progressive torque increase at all angles over the 16-month period, with a steeper slope at the training angle. Contrary to the specificity of training concept, angle-specific strengthening in midrange may be sufficient to strengthen the extensors surrounding an osteoarthritic knee through a wide range of motion. Mid-range isometric strengthening exercises might thus prove useful in the rehabilitation of patients with knee osteoarthritis who are unable to exercise their weakened quadriceps at other angles due to pain or swelling.