Effects of isometric quadriceps activation on the Q-angle in women before and after quadriceps exercise.

Abstract

Single-group test-retest design with correlation analysis. (1) To confirm that the Q-angle decreases with isometric quadriceps activation (IQA), (2) to determine if the decrease in the Q-angle with IQA is related to the magnitude of the Q-angle at rest, and (3) to determine if a vigorous bout of exercise affects the change in the Q-angle with IQA. The Q-angle represents an estimate of the resultant force of the quadriceps on the patella and is a predictor of lateral movement of the patella under dynamic conditions. Q-angles were assessed in 22 nonimpaired women (mean +/- SD age, 22.3 +/- 4.9 years) while standing relaxed and during IQA. Subjects then rode a cycle ergometer until a preset number of repetitions per minute was unable to be maintained. Q-angles were again assessed while subjects were relaxed and during IQA. There was a significant decrease (mean +/- SD, 5.7 +/- 4.2 degrees) in the Q-angle with IQA compared with relaxed standing. There was a significant relationship (r=0.72) between the Q-angle at rest and the change with IQA. The cycle ergometer exercise resulted in a small (0.5 degrees) but significantly greater decrease in the Q-angle with IQA compared with relaxed standing. The Q-angle decreases with IQA, and the magnitude of this decrease is dependent on the magnitude of the Q-angle at rest. Our findings support the view that an excessive Q-angle may predispose women to greater lateral displacement of the patella during vigorous activities and sports in which the quadriceps muscle is stressed.