This case report describes the effect of strengthening the quadriceps of an effused osteoarthritic knee joint of a 53-year-old man isometrically in mid-range. The instruments included an isokinetic dynamometer, a knee scoring inventory, and a visual analog scale. The outcome measures of isometric quadriceps torque and work, clinical status, and pain were recorded before and after the exercise intervention. The exercises were carried out three times per week for a 6-week period with the subject seated on an exercise chair. Following training, quadriceps torque increased, clinical status improved, and pain with walking decreased. Subject to further investigation, isometric training of the quadriceps in mid-range could prove useful for improving the function of persons with painful or effused knees who might otherwise experience muscle inhibition by exercising in the more traditional inner ranges of knee extension.