Background: The craniocervical flexion (CCF) exercise is one of the effective exercise in correcting forward head posture (FHP). However, some people with FHP achieve CCF with compensatory movements, for example, low cervical flexion using superficial neck flexors such as the sternocleidomastoid (SCM) muscle. No study has yet investigated whether a dualpressure biofeedback unit (D-PBU) method to prevent low cervical flexion would be helpful in performing pure CCF movement. Objects: The purpose of this study was to compare the effects of the CCF using D-PBU method and the traditional CCF method on the cross-sectional area (CSA) of the longus colli muscle (LCM) and the activity of SCM muscle in subjects with FHP. Methods: Twentyfour FHP subjects (male: 16, female: 8) were recruited for this study. All subjects performed CCF using two different methods: The traditional CCF method and the CCF using D-PBU method. The CSA of the LCM was measured via ultrasound, and surface electromyography was used to measure SCM muscle activity. Results: The change in CSA of the LCM was significantly larger during the CCF using D-PBU method (1.28±.09) compared with the traditional CCF method (1.19±.08) (p<.05). The SCM muscle activity using the CCF using D-PBU method (2.01±1.97 %MVIC) was significantly lower than when using the traditional CCF method (2.79±2.32 %MVIC) (p<.05). Conclusion: The CCF using D-PBU method can be recommended for increasing LCM activation and decreasing SCM muscle activity during CCF movement in subjects with FHP.

Abstract
 Introduction
 Methods
  Subjects
  Instrumentations and data processing
  Procedure
  Statistical analysis
 Results
 Discussion
 Conclusion
 References

• Min-chan Son(Kinetic Ergocise Based on Movement Analysis Laboratory, Dept. of Physical Therapy, The Graduate School, Yonsei University)
• Ui-jae Hwang(Kinetic Ergocise Based on Movement Analysis Laboratory, Dept. of Physical Therapy, The Graduate School, Yonsei University)
• Sung-hoon Jung(Kinetic Ergocise Based on Movement Analysis Laboratory, Dept. of Physical Therapy, The Graduate School, Yonsei University)
• Sun-hee Ahn(Kinetic Ergocise Based on Movement Analysis Laboratory, Dept. of Physical Therapy, The Graduate School, Yonsei University)
• Hyun-a Kim(Kinetic Ergocise Based on Movement Analysis Laboratory, Dept. of Physical Therapy, The Graduate School, Yonsei University)
• Oh-yun Kwon(Kinetic Ergocise Based on Movement Analysis Laboratory, Dept. of Physical Therapy, College of Health Science, Yonsei University, Dept. of Ergonomic Therapy, The Graduate School of Health and Environment, Yonsei University) Corresponding author