Citation: 

Saito, A., & Akima, H. (2015). Neuromuscular Activation of the Vastus Intermedius Muscle during Isometric Hip Flexion. PloS one, 10(10), e0141146. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4619471/ 
 

Neuromuscular Activation of the Vastus Intermedius Muscle during Isometric Hip Flexion 

Summary

Saito, and Akima (2015) conducted research on the activation of the vastus intermedius versus the rectus femoris during isometric hip flexion. With the quadriceps femoris aiding in knee extension, the bi-articular muscle of those being the rectus femoris also aids in hip flexion. Previous literature displays evidence that the vastus intermedius and the rectus femoris may be able to coactivate during certain phases of walking or running that involves hip flexion. Due to the fact that the researchers knew the vastus intermedius and rectus femoris coactivated during hip flexion movements, they decided to conduct a study at what magnitude does the vastus intermedius activate during isometric hip flexion tests (Saito, and Akima, 2015). 

Saito, and Akima’s study (2015) involved gathering 10 healthy men of various ages with a health background of no previous knee surgery. The men had physical activities levels ranging from untrained to those that partake in physical activity regularly. All participants were briefed on the study, then asked to provide consent for testing purposes. The first phase of testing with the subjects involved placing the hip joint at angles of 90 degrees, 110 degrees and 130 degrees then performing muscular voluntary contractions of an isometric knee extension. The testing then involved a hip joint angle of 90 degrees and performing isometric knee flexion task. The contractions were to be performed twice for a duration of 3 seconds, then followed by a rest period equivalent to or greater than 1 minute between attempts. An additional attempt occurred if the torque being generated differed by more than 5% value than the previous knee torque. The second phase of testing with the subjects included performing voluntary contractions of hip flexion during hip joint angles of 90 degrees, 110 degrees, and 130 degrees.  

Participants completed three submaximal contractions of various submaximal target torques of 25%, 50%, and 75% of the maximal voluntary contraction with a rest duration equivalent to or greater than one minute. The duration of contraction lasted for 3 seconds while sustaining the torque target line. To gather the information, researchers recorded EMG signals through electrodes attached to the vastus intermedius, vastus lateralis, and vastus medialis, rectus femoris, and bicep femoris. Electrodes were placed in designated areas after the location on the limb was properly prepped and specific tools were utilized to locate proper electrode placement. The data collected by the researchers were gathered via IBM SPSS statistics software. Researchers analyzed hip flexion and isometric knee extension torque during maximal voluntary contractions at the observed joint angles utilizing a “two-way (hip joint angle × movement) analysis of variance (ANOVA) with repeated measures (Saito, and Akima, 2015).” The researchers then observed the EMG signals from the quadriceps femoris muscles during the hip flexion tasks and analyzed them using “a two-way (muscle × torque and hip joint angle) ANOVA with repeated measures (Saito, and Akima, 2015).” The study stated a delay of the vastus intermedius activation after the rectus femoris, which was 230–240 ms. This delay in time between the activation of the two muscles during isometric flexion and knee extension was also analyzed via a “two-way (hip joint angle × movement) ANOVA with repeated measures (Saito, and Akima, 2015).” P < 0.05 was established as the level of statistical significance. Maximal voluntary contractions during hip flexion and knee extension differed in torque exertion. Maximal voluntary contraction of isometric hip flexion torque for the joint angle of 90 degrees (134.8 ± 18.4 Nm) was less than the torque of 110 degrees (161.0 ± 23.6 Nm) and 130 degrees (171.7 ± 23.8 Nm). The maximal voluntary contraction of isometric knee extension torque did not differ greatly between the different hip joint angle (90 degrees, 110 degrees and 130 degrees; 197.3 ± 39.5, 212.9 ± 45.8 and 213.2 ± 53.9 Nm respectively). During the normalized EMG, the RF showed significant higher maximal voluntary contraction than the vastus intermedius, vastus lateralis, and vastus medialis. The vastus intermedius showed higher contraction levels than the vastus medialis when the high joint angle was 110 degrees and 130 degrees. These results provide evidence that during hip flexion, the rectus femoris activates prior to the vastus intermedius.  

Reflection & Application

 
The research that Saito, and Akima (2015) published gave me better insight on the role that the individual quadriceps femoris muscles play during either knee extension or hip flexion. Both movements are essential and vital functions during day to day tasks such as walking or running. Given the data collected by the provided study, we can conclude that the vastus intermedius might be seen as a secondary support system for stability during knee or hip function (depending on movement). With the muscle being activated after the rectus femoris, training selection for that area of stability might have to involve a longer contractile time frame, allowing the muscle to fully respond to the stimulus. This could mean setting a given tempo for concentric phases of exercises, as long as the individual partaking in the fitness training consciously follows the protocol. Then, we would also have to explore the activation and recruitment of the vastus intermedius during the eccentric function of the quadriceps. If the individual is going through a loaded squat movement, this loads the quadricep femoris muscles during an eccentric phase creating hip flexion, but also generating knee flexion. The study evaluated knee extension or hip flexion, but what if knee flexion and hip flexion occur in the same movement? What does that mean for vastus intermedius recruitment? I believe this study could be an amazing tool for studies ahead. Although the results provide a great understanding about the role of the vastus intermedius, I think that the data provides a starting point in which researchers could begin in any given direction. There isn’t a set second step to the research that could branch from this study. The researchers could continue to understand that particular muscle in the quadriceps femoris, look at different movement patterns effected by those muscles, or even compare different ages or genders on muscular development and muscle fiber recruitment. With that being said, I believe the study was very unorganized when it came to participant selection. There were only 10 subjects being evaluated, and even then, the physical fitness and activity level was not regulated. It would have been a better study if the researchers had maybe gathered 10 beginner, 10 intermediate, and 10 elite level athletes that would at least illustrate a sense of ranking level and muscular development. I don’t believe the study was a waste at all, since it did provide a baseline for the understanding of these muscle groups. I chose this study because I love understanding the mechanics of the body. As I continue to learn, I can implement the knowledge gained toward programs that encourage injury prevention. With injury prevention comes prehab and return to work recovery protocols. I do believe a deeper understanding of human anatomy, biomechanics, and exercise science will highly benefit my programs as they continue to develop. 

Author: Hussien Jabai

Contact via email at Hussien@jabaiperformance.com