Study Design: Single group repeated measures design. Objective: To determine if the rate of transition between knee flexion and extension influences the subsequent concentric activation of the quadriceps and knee extension torque during reciprocal movements. Background: Preloading a muscle by stretching, a prior isometric or eccentric muscle action, or a prior movement controlled concentrically by the antagonist muscle group increases the maximal torque-generating capability of the agonist. We hypothesized that the rate of transition from the prior movement may be the critical factor that influences the degree of muscle facilitation and torque potentiation. Rapid reversal of antagonistic movements has been postulated as a potential facilitatory mechanism. Methods: Knee extension torque and electromyographic (EMG) amplitude (dependent variables) from 2 of the vasti muscles were recorded while subjects (N = 20; 12 men, 8 women, mean age, 28.5 ± 2.68 years) maximally activated their quadriceps at 3 constant angular velocities, 100°/s, 200°/s, and 300°/s, and 2 preload conditions, SLOW and RAPID (independent variables). In the SLOW transition condition, subjects actively flexed their knee to 110° from an extended position, paused in this position for 3 seconds, and then extended to O°. In the RAPID transition condition, the same movement from knee flexion to extension was performed without a pause. Results: Peak torque, the root-mean-square (RMS) average, peak (peak rectified and smoothed), and initial (100 milliseconds prior to torque onset) EMG amplitudes were all significantly greater during the RAPID transition condition. Peak torque decreased with increasing movement velocity. There were no interactions between the preload conditions and angular velocity on peak torque or the EMG amplitude variables. There was also no influence of velocity on the EMG amplitude variables. Conclusions: The effect of preloading the quadriceps by prior concentric activation of the hamstrings is dependent on the rate of transition between the flexion and extension movements and is due primarily to neural facilitation.

J Orthop Sports Phys Ther. 2001;31(4):122-132.

Key Words: exercise, muscle training. proprioceptive neuromuscular facilitation, quadriceps

Study Design: Single-group test-retest design with correlation analysis. Objectives: (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. Background: 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. 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. 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. Results: There was a significant decrease (mean ± SD, 5.7 ± 4.2°) 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°) but significantly greater decrease in the Q-angle with IQA compared with relaxed standing. Conclusions: 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.

J Orthop Sports Phys Ther. 2000;30(4):211-216.

Key Words: patellofemoral joint