Research article - (2020)19, 630 - 636 |
Influence of Altered Knee Angle and Muscular Contraction Type on Electromyographic Activity of Hamstring Muscles during 45° Hip Extension Exercise |
Taspol Keerasomboon1, Shinshiro Mineta2, Norikazu Hirose3, |
Key words: Biceps femoris, knee flexion, external resistance, sports, injuries |
Key Points |
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Subjects |
Twenty-two recreationally active male volunteers who perform aerobic activity at least twice a week (mean age, 22.1 ± 2.0 years; height, 1.73 ± 0.05 m; and body mass, 65.5 ± 7.6 kg, all measured in mean ± standard deviation [SD]) participated in this study. Subjects with hamstring strain and any other injury were excluded. The study was approved by the Human Research Ethics Committee of the University and was conducted in accordance with their guidelines for human experimentation. All subjects provided written informed consent prior to participation. |
Procedures |
Before the experiment, subjects were prepared for EMG electrode placement by shaving the hair around the target site and the skin was cleaned with alcohol. The six target muscles (BFl, ST, SM, GM, AD, and ES) were measured using wireless EMG sensors (m-BioLog2 DL-5000, S&ME Co., Ltd., Tokyo, Japan). The EMG electrodes were preamplified (10X) and linked through the EMG mainframe, which further amplified it (100X) to a total gain of 1,000X, and band pass filtered (20-500 Hz) the signals. The electrodes were placed on each target muscle following the landmarks: midpoint between the ischial tuberosity and the lateral epicondyle of the tibia (BFl), midpoint of the line between the ischial tuberosity and the media epicondyle of the tibia (ST), on the line between medial condyle of the tibia and ischial tuberosity (SM), midpoint between the sacral vertebrae and the greater trochanter (GM), two finger-width lateral from the spinous process of the L1 vertebra (ES), and two finger-width lateral from the midline of the umbilicus (AD). Electrodes were placed parallel to the lines between these landmarks as recommended in the SENIAM guidelines (Hermens et al., After performing the MVIC protocol, subjects performed three bouts of 45° hip extension exercises in 4 different knee flexion angles (total 12 bouts). The knee flexion angle was randomly set at 0°, 45° or 90°. A manual goniometer was used to monitor the knee joint angle at the start of each exercise. During the exercise protocol, subjects were instructed to hold their back erect and kneel on the adjustable incline board plan covered with an exercise mat at 45° angle above the ground. Then, subjects adjusted their knee flexion angles and their legs were held by the examiner to stabilize the knee flexion angle. Subjects were instructed to bend their back forward to a 0° hip joint angle and hold it for 5 seconds (neutral isometric phase [(ISO0]). Next, the subjects were instructed to gradually bend their back forward to a 45° hip joint angle for 5 seconds (eccentric phase [ECC]), and then hold the position for 5 seconds (isometric phase during hip extension [ISO45]). Finally, subjects were instructed to gradually elevate their back up to a 0° hip joint angle for 5 seconds (concentric phase [CON]). During this cross-over study, subjects performed each protocol in non-weight-bearing (NW) and 5 kg weight-bearing (5WT) conditions. |
Statistical Analyses |
The average value (+SD) of each exercise was calculated. The RMS data were normalized as a percentage of the maximum isometric values (normalized EMG [nEMG]). A multivariate analysis of variance (MANOVA) with repeated measures using syntax was used to compare the nEMG of each muscle across different knee joint angles in each weight condition. In addition, the t-test was used to compare the difference between NW and 5WT conditions for each muscle and degree. When a simple main effect was found, Tukey post hoc test was used to measure any differences. The statistical power was analyzed using SPSS for Windows, Version 25.0 (IBM Corp., Armonk, NY, USA). The statistical significance level was set at a P-value < 0.05. |
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Comparison between knee angles for each muscle |
The obtained nEMG activity values during exercise in the ISO0, ISO45, ECC and CON contraction conditions are shown in |
Comparison between muscles for each knee angle |
There was a significant main effect between muscles in both the NW and 5WT conditions during ISO0, ISO45, ECC and CON (all p < 0.05). The nEMG activity of the BFl was significantly higher than that of the SM at 90° knee flexion angle in both the NW and 5WT conditions during ISO0, ISO45, ECC and CON, except for ECC in the NW condition (p < 0.05). However, there were no significant interactions between muscles and angles. In related muscles (ES, GM and AD), there was a significant main effect between muscles in both the NW and 5WT conditions during ISO0 and CON, respectively (p < 0.05). The nEMG activity in the ES was significantly higher than that in the GM and AD at 0° of the knee flexion angle during ISO0 and CON. |
Comparison between NW and 5WT for each muscle and angle |
We found no main effect between NW and 5WT conditions for all exercises and no interaction between knee angle and load. |
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In this study, we examined the recruitment patterns of each hamstring muscles during a 45° hip extension across different knee flexion angles during ISO0, ISO45, ECC and CON in the NW and 5WT conditions. We found that the EMG activity of the BFl was higher at increasing knee flexion angles (45° and 90°). The results indicated that the BFl worked harder at a deep knee flexion angle than the other two hamstring muscles and this finding differs from those of previous report (Onishi et al., In this study, we showed that the nEMG activity of the BFl was significantly higher than that of the SM at 90° of the knee flexion in both the NW and 5WT conditions during ISO0, ISO45, ECC and CON (p < 0.05), except during ECC in the NW condition. In related muscles, nEMG activity of the ES was significantly higher than that of the GM and AD at 0° of the knee flexion during ISO0, ECC and CON except for ECC in the 5WT condition. This result implied that the EMG activity of the BFl was similar to that of the ST during 45° hip extension. Our findings differ from that of a previous study on hamstring recruitment by Bourne et al. ( In contrast, our participants were instructed to flex and extend the hip until they reached a point 45° from the starting position and this difference led to the different muscle lengths during hamstring contraction. However, Bourne et al. (2017) also examined the muscle activation by using functional magnetic resonance imaging (fMRI), which is effective in showing the reliance on different hamstring muscles during each exercise. They reported that 45° hip extension heavily recruit both BFl and ST. These findings are consistent with the EMG component of our study, which showed similar BFl and ST activation. Mohamed et al. ( Several factors, such as differences in morphological features and the number of joint recruitments, may be responsible for the difference in the EMG activity of the hamstring at different knee joint angles. The BFl muscles are composed of unipennate fibers which have large cross-sectional areas, making them more suitable for torque production than the ST, which has a fusiform shape (Mohamed et al., This study had several limitations, the first of which was the uncontrollable intensity during 45° hip extension. In the 5WT condition, all participants were instructed to hold a 5 kg weight; however, the effect of this weight-bearing may differ between participants because of each individual’s strength. Further studies are required to determine the intensity of weight-bearing effect on each participant during exercise. We need to conduct further research to clarify the mechanisms of different joint angles and compare different hamstring exercises to identify the most effective exercise for preventing hamstring strains. |
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Previous study argued that the motor unit recruitment can not be inferred from changes in sEMG amplitude. However, some studies which indicated that a high level of nEMG is an important indicator of improved strength and that the establishment of voluntary activation exercises prevent hamstring strains, may have implications for rehabilitation (Bourne et al., |
ACKNOWLEDGEMENTS |
The authors would like to acknowledge the facilities and the assistance of graduate school of sport science, Waseda University. The experiments comply with the current laws of the country in which they were performed. The authors have no conflict of interest to declare. |
AUTHOR BIOGRAPHY |
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REFERENCES |
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