Background: The superimposed technique (ST) involves the application of electrical muscle stimulation (EMS) during voluntary muscle action. The physiological effects attributed to each stimulus may be accumulated by the ST. Although various EMS devices for the quadriceps muscle are being marketed to the general public, there is still a lack of research on whether ST training can provide significant advantages for improving quadriceps muscle strength or thickness compared with EMS alone. Objective: To compare the effects of eight weeks of ST and EMS on the thicknesses of the rectus femoris (RF) and vastus intermedius (VI) muscles and knee extension strength. Methods: Thirty healthy subjects were recruited and randomly assigned to either the ST or EMS groups. The participants underwent ST or EMS training for eight weeks. In all participants, the thicknesses of the RF and VI muscles were measured before and after the 8-week intervention by ultrasonography, and quadriceps muscle strength was measured using the Smart KEMA tension sensor (KOREATECH Co., Ltd.). Results: There were significant differences in the pre- and post-intervention thicknesses of the RF and VI muscles as well as the quadriceps muscle strength in both groups (p < 0.05). RF thickness was significantly greater in the ST group (F = 4.294, p = 0.048), but there was no significant difference in VI thickness (F = 0.234, p = 0.632) or knee extension strength (F = 0.775, p = 0.386). Conclusion: EMS can be used to improve quadriceps muscle strength and RF and VI muscle thickness, and ST can be used to improve RF thickness in the context of athletic training and fitness.

Background: Although rectus femoris (RF) eccentric training and static stretching (SS) have been reported effectively on lumbar flexibility, and muscle architecture, most studies are results using machines and long-term effects. Therefore, we want to investigate the effect of Reverse Nordic Hamstring Exercise (RNHE), a self-eccentric training, by immediately comparing it with SS. Objectives: To compare the RNHE and SS of RF to show the effects of lumbar flexibility, and fascicle length (FL). Design: Randomized controlled trial. Methods: A total of 30 study subjects were randomly allocated into an experimental group(Reverse Nordic Hamstring Exercise) and a control group(Static Stretching). Before and after the intervention, the subject performed fingertip to floor test (FFT) to evaluate the flexibility of the lumbar spine and measured FL through the SONON 300L (Healcerion Inc., Seoul, South Korea). Results: There was a significant effect on lumbar flexibility within both groups (P<.05), also there were clear results between the two groups (P<.05). FL showed a significant increase in RNHE (P<.05), but not in SS, and there was a no significant difference between the two groups. Conclusion: RNHE is effective in improving lumbar flexibility, and FL of RF muscle.

Background: Whole body-electromyostimulation (WB-EMS) is widely used for the rehabilitation and recovery of patients with various neuromusculoskeletal disorders. Objects: To objectively measure changes in lower extremity and abdominal muscles after sit-to-stand dynamic movement training using WB-EMS. Methods: A total of 46 healthy adults (23 experimental and 23 control subjects) performed sit-to-stand exercise; the experimental group with WB-EMS, and the control group without WB-EMS. The muscle activity of the lower extremity, and the muscle thickness of the lower extremity and abdominal muscles were measured before and after the intervention. Results: In terms of electromyographic activity, there was a significant interaction effect for the rectus femoris (RF) muscle (F=30.212, p=.000). With regards to ultrasonographic imaging, the muscle thickness of the RF muscle had a significant interaction effect at the muscle contraction ratio (F=8.071, p=.007). The deep abdominal muscles, such as the transverse abdominal (TrA) and internal oblique (IO) muscles, also showed significant interaction effects at the muscle contraction ratio (F=5.474, p=.024, F=24.151, p=.000, respectively) Conclusion: These findings suggest that WB-EMS may help to improve the muscular activity of the RF muscle, and the muscle thickness of the RF muscle and deep muscles such as the TrA and IO muscles.