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

Study Design: Single-group test-retest design with correlation analysis. Objectives: (1) To confirm that the Q-angle decreases with isometric quadri ceps 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 determi ne if a vigorous bout of exercise affects the change in the Q-angle with IQ A. Background: The Q-angle represents an estimate of the resultant force of th e quadriceps on the patella and is a predictor of lateral movement of the p atella under dynamic conditions. Methods and Measures: Q-angles were assessed in 22 nonimpaired women (mean +/- SD age, 22.3 +/- 4.9 years) while standing relaxed and during IQA. Subj ects then rode a cycle ergometer until a preset number of repetitions per m inute was unable to be maintained. Q-angles were again assessed while subje cts were relaxed and during IQA. Results: 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 significa nt 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 sig nificantly greater decrease in the Q-angle with IQA compared with relaxed s tanding. Conclusions: The Q-angle decreases with IQA, and the magnitude of this decr ease is dependent on the magnitude of the Q-angle at rest. Our findings sup port the view that an excessive Q-angle may predispose women to greater lat eral displacement of the patella during vigorous activities and sports in w hich the quadriceps muscle is stressed.