Revisiting the influence of hip and knee angles on quadriceps excitation measured by surface electromyography : original research article

Background: The quadriceps muscle group includes one biarticular (crosses the hip and the knee) and three monoarticular (crosses the knee only) muscles. The influence of hip and knee angles on quadriceps muscles excitation remains inconclusive in the literature. Research question: To re-examine the excitation of the biarticular and monoarticular quadriceps muscles during maximum voluntary isometric contractions at different hip and knee angles. Type of study: Cross-sectional experimental study. Methods: Ten recreationally active subjects (5 males, 5 females) performed maximum voluntary isometric contraction of knee extensors at six knee angles (90°, 100°, 110°, 120°, 130° and 140°) on an isokinetic dynamometer. The protocol was repeated at three hip positions: sitting, inclined and supine. During the test, surface electromyography was employed to record muscle activity of the rectus femoris (RF), vastus lateralis (VL) and vastus medialis (VM). Repeated measures ANOVA (hip x knee) was used to determine the effect of hip and knee angles on peak torque and muscle excitation. Results: A significant hip by knee interaction was found for RF (P = 0.013). As the knee angle increased, VL and VM excitation decreased (P < 0.001). Higher excitation was observed in the sitting position, followed by inclined and then the supine position for both VL (P = 0.004) and VM (P = 0.046). Conclusions: As expected, changes in knee angle influence the excitation of all surface quadriceps muscles. However, changes in hip angle, though only alter the biarticular muscle length, influence both biarticular and monoarticular muscle excitation. The large discrepancy among studies warrants further attention.