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Kim Y1, Oh D1, Park H2, Lee T3, Yang D4, Lee J5, Ahn J6, Lim W1,7
1Woosong University, Physical Therapy, Daejeon, Korea (South), 2Good Daycare Center, Daejeon, Korea (South), 3Dong-eui Institute of Technology, Busan, Korea (South), 4Good Morning Clinic, Daejeon, Korea (South), 5Synergycare Physical Therapy, New York, United States, 6SYM Pilates Studio, Seoul, Korea (South), 7Woosong Institute of Rehabilitation Science, Daejeon, Korea (South)
Background: Exercise-induced muscle damage more frequently occurs in the lower limbs than in the upper limbs. Most cases of lower limb muscle damage occur in the hamstrings. The 3 hamstring muscles each has unique anatomical and contractile properties. Hence, each muscle should be investigated separately. Previous studies on hamstrings investigated the magnitude of contraction of the muscles at different knee angles during maximum voluntary isometric contraction (MVIC). However, no studies have investigated submaximal contraction.
Purpose: The purpose of this study was as follows:
1) To compare the EMG activities of the biceps femoris (BF), semitendinosus (ST), and semimembranosus (SM) with respect to voluntary isometric contractions at different intensities and
2) to compare the functional aspects of the hamstrings before and after submaximal isometric contraction.
Methods: Subjects (19 men and 14 women; age, 21.46 ± 1.57 years; height, 168.27 ± 9.15 cm; weight, 65.39 ± 14.39 kg) included in this study had decreased hamstring flexibility and active knee extension (AKE) of 20°. The contraction strengths in each group were set to MVICs of 60% (P60) and 20% (P20). The subjects were randomly distributed into the groups. Voluntary isometric contractions were performed 5 times for 6 seconds each. By using a surface EMG, muscle activities of the BF, ST, and SM were measured. The subjects were asked to perform vertical jumps before and after the EMG measurement.
Results: Significant differences among the muscle activities of the BF, ST, and SM at P60 and P20 were observed. At P60 and P20, the muscle activities of the BF, ST, and SM were 58.9 ± 28.0 and 35.4 ± 11.4, 61.8 ± 16.0 and 44.9 ± 20.1, and 60.4 ± 19.5 and 40.4 ± 16.2, respectively. Although vertical jump height was significantly decreased after voluntary isometric contraction in the P60 group (p = 0.030), no changes were observed in the P20 group (p = 0.162).
Conclusion(s): At the SLR position, the gluteus maximus and hamstring muscles are the primary muscles that carry out hip extension. In the P60 group, all three muscles showed a decrease to 38.1-41.1% as compared with MVIC. On the other hand, the P20 group showed a decrease to 55.1-64.6%. The results indicate that the hamstring muscle activities are preserved at low-intensity voluntary isometric contraction. Although P60 caused a decrease in hamstring function, P20 did not.
Implications: To selectively activate hamstring muscles among the hip extensors, low-intensity isometric contraction would be helpful. Furthermore, when proprioceptive neuromuscular facilitation stretching, also called isometric contraction, is performed on the lower extremity to increase its flexibility, low-intensity hamstring contraction could be a wise choice, as it does not cause decreased muscular functions.
Keywords: Electromyography, Isometric contraction, Intensity
Funding acknowledgements: 2018 Woosong University Academic Research Funding and a Basic Science Research Program(NRF-2017R1C1B5076885)
Purpose: The purpose of this study was as follows:
1) To compare the EMG activities of the biceps femoris (BF), semitendinosus (ST), and semimembranosus (SM) with respect to voluntary isometric contractions at different intensities and
2) to compare the functional aspects of the hamstrings before and after submaximal isometric contraction.
Methods: Subjects (19 men and 14 women; age, 21.46 ± 1.57 years; height, 168.27 ± 9.15 cm; weight, 65.39 ± 14.39 kg) included in this study had decreased hamstring flexibility and active knee extension (AKE) of 20°. The contraction strengths in each group were set to MVICs of 60% (P60) and 20% (P20). The subjects were randomly distributed into the groups. Voluntary isometric contractions were performed 5 times for 6 seconds each. By using a surface EMG, muscle activities of the BF, ST, and SM were measured. The subjects were asked to perform vertical jumps before and after the EMG measurement.
Results: Significant differences among the muscle activities of the BF, ST, and SM at P60 and P20 were observed. At P60 and P20, the muscle activities of the BF, ST, and SM were 58.9 ± 28.0 and 35.4 ± 11.4, 61.8 ± 16.0 and 44.9 ± 20.1, and 60.4 ± 19.5 and 40.4 ± 16.2, respectively. Although vertical jump height was significantly decreased after voluntary isometric contraction in the P60 group (p = 0.030), no changes were observed in the P20 group (p = 0.162).
Conclusion(s): At the SLR position, the gluteus maximus and hamstring muscles are the primary muscles that carry out hip extension. In the P60 group, all three muscles showed a decrease to 38.1-41.1% as compared with MVIC. On the other hand, the P20 group showed a decrease to 55.1-64.6%. The results indicate that the hamstring muscle activities are preserved at low-intensity voluntary isometric contraction. Although P60 caused a decrease in hamstring function, P20 did not.
Implications: To selectively activate hamstring muscles among the hip extensors, low-intensity isometric contraction would be helpful. Furthermore, when proprioceptive neuromuscular facilitation stretching, also called isometric contraction, is performed on the lower extremity to increase its flexibility, low-intensity hamstring contraction could be a wise choice, as it does not cause decreased muscular functions.
Keywords: Electromyography, Isometric contraction, Intensity
Funding acknowledgements: 2018 Woosong University Academic Research Funding and a Basic Science Research Program(NRF-2017R1C1B5076885)
Topic: Sport & sports injuries
Ethics approval required: Yes
Institution: Woosong University
Ethics committee: Institutional Review Board of Woosong University
Ethics number: 1041549-180419-SB-59
All authors, affiliations and abstracts have been published as submitted.
