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.

INTRODUCTION
MATERIALS AND METHODS
    1. Subjects
    2. Electrical Muscle Stimulation Training
    3. Superimposed Technique Training
    4. Assessment of Quadriceps Muscle Thickness
    5. Measurement of Quadriceps Muscle Strength
    6. Procedures
    7. Statistical Analysis
RESULTS
DISCUSSION
CONCLUSIONS
FUNDING
ACKNOWLEDGEMENTS
CONFLICTS OF INTEREST
AUTHOR CONTRIBUTIONS
ORCID
REFERENCES

• Young-soo Weon(Department of Physical Therapy, The Graduate School, Yonsei University, Kinetic Ergocise Based on Movement Analysis Laboratory)
• Jun-hee Kim(Kinetic Ergocise Based on Movement Analysis Laboratory, Department of Physical Therapy, College of Health Science, Yonsei University, Wonju, Korea)
• Gyeong-tae Gwak(Kinetic Ergocise Based on Movement Analysis Laboratory, Department of Physical Therapy, College of Health Science, Yonsei University, Wonju, Korea)
• Do-eun Lee(Department of Physical Therapy, The Graduate School, Yonsei University, Kinetic Ergocise Based on Movement Analysis Laboratory)
• Oh-yun Kwon(Kinetic Ergocise Based on Movement Analysis Laboratory, Department of Physical Therapy, College of Health Science, Yonsei University, Wonju, Korea) Corresponding author