The Effects of Contraction intensity on Quadriceps Femoris Muscle Recruitment

Abstract

1224 Introduction: Previous work has suggested that differential recruitment of the separate portions of the superficial quadriceps femoris muscle varies as a function of voluntary contraction intensity, and tends to converge at near-maximal intensities (Alkner et al, Med Sci Sports Exerc, 2000; Pincivero and Coelho, Muscle Nerve, 2000). Purpose: To examine recruitment behavior of the superficial quadriceps femoris muscle across different contraction intensities. Procedures: Thirty-seven physically active young adults (12 men, 25 women) performed five isometric maximal voluntary contractions (MVC) at 90 deg knee flexion on a Biodex isokinetic dynamometer. The mean peak torque was calculated from the three highest values. Subjects then performed five s isometric knee extension contractions from 10 to 90% MVC, in 10% increments, in random order. Muscle recruitment was evaluated via electromyography (EMG) from the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) muscles. EMG signals were collected at 2000 Hz, band pass filtered, full-wave rectified, integrated over the middle three seconds of each isometric contraction, and normalized to the MVC. Descriptive statistics and repeated measures analysis of variance (ANOVA) of muscle and intensity was conducted. Statistical significance was determined at p<0.05. Results: The results demonstrated significant differences between the three muscles at 10% (F2,72 = 5.47, p = 0.006), 20% (F2,72 = 3.32, p = 0.041), and 30% (F2,72 = 6.89, p = 0.002) MVC intensities. Pair-wise comparisons demonstrated significant differences between the VM (5.10 ± 2.06%) and VL (6.88 ± 1.86%), and between the VM and RF (7.24 ± 1.75%) at 10% MVC. At 20% MVC, significant differences were found between VM (12.41 ± 1.80%) and VL (15.62 ± 1.64%). Significant differences were found between VM (20.83 ± 1.77%) and VL (24.90 ± 1.24%), and VL and RF (17.71 ± 1.40%) at the 30% intensity. CONCLUSIONS: The major findings demonstrate that the recruitment behavior of the different portions of the superficial quadriceps femoris muscle, are similar across moderate to near-maximal voluntary contraction intensities.