Background: Chronic low back pain (CLBP) causes morphological changes in muscles, reduces muscle strength, endurance and flexibility, negatively affects lumbar stability, and limits functional activity. Plank exercise strengthens core muscles, activates abdominal muscles, and improves intra-abdominal pressure to stabilize the trunk in patients with CLBP.
Objects: We investigated the effect of plank exercise on abdominal muscle thickness and disability in patients with CLBP.
Methods: We classified 33 subjects into 2 groups: An experimental (n1=17) and a control group (n2=16). Patients in the experimental group participated in plank exercise and those in the control group participated in stretching exercise. Patients in both groups attended 20-minute exercise sessions thrice a week for 4 weeks. Abdominal muscle thickness in each subject was evaluated ultrasonographically, and disabilities were assessed using the Oswestry disability index (ODI).
Results: Four weeks later, abdominal muscle thickness showed a significant increase over baseline values in both groups (p<.05). Patients in the experimental group reported a more significant increase in the thickness of the external oblique muscle than that in the control group (p<.05). ODI scores in the experimental group were significantly lower after intervention than before intervention (p<.05).
Conclusion: Plank exercise increases the thickness of the external oblique muscle and reduces disability secondary to mild CLBP. Therefore, plank exercise is needed to improve lumbar stability and functional activity in patients with mild CLBP.

Abstract
 Ⅰ. 서론
 Ⅱ. 연구방
  1. 연구대상자
  2. 측정 도구
  3. 측정 방법
  4. 중재 방법
  5. 분석방법
 Ⅲ. 결과
  1. 연구 대상자의 일반적인 특성
  2. 군과 시간의 상호작용 효과와 시간에 따른 주효과 비교
  3. 중재 전후와 군에 따른 ODI 변화 비교
 Ⅳ. 고찰
 Ⅴ. 결론
 References

• 정혜진(전주대학교 의과학대학 물리치료학과) | Hye-jin Jeong (Dept. of Physical therapy, College of Medical Science, Jeonju University)
• 하수진(전주대학교 의과학대학 물리치료학과) | Su-jin Ha (Dept. of Physical therapy, College of Medical Science, Jeonju University)
• 정예지(전주대학교 의과학대학 물리치료학과) | Ye-ji Jeong (Dept. of Physical therapy, College of Medical Science, Jeonju University)
• 조우현(전주대학교 의과학대학 물리치료학과) | Woo-hyun Cho (Dept. of Physical therapy, College of Medical Science, Jeonju University)
• 김준기(전주대학교 의과학대학 물리치료학과) | Jun-ki Kim (Dept. of Physical therapy, College of Medical Science, Jeonju University)
• 원종임(전주대학교 의과학대학 물리치료학과) | Jong-im Won (Dept. of Physical therapy, College of Medical Science, Jeonju University) Corresponding author