背景與目的：有鑑於以超音波測量腹部肌群肌肉厚度並同時涵蓋三個腹部區域的文獻很少，因此本研究的目的在於以超音波來量測所有腹部肌群之肌肉厚度與其對稱性，以探討健康女性其腹部肌群在不同位置間與不同肌肉間之厚度差異，並驗證初學施測者使用超音波測量腹肌厚度之施測者間信度。方法：本研究中共徵求30位女性健康自願受試者（平均年齡為20.6±1.9歲），以軟組織超音波設備（7.5MHz直線性探頭）造影，在影像定格後以游標系統直接在螢幕上測量腹直肌、腹內斜肌、腹外斜肌與腹橫肌之厚度。先驗證兩位初學者之施測者間信度，並以組內相關係數(intra-class correlation coefficient, ICC)、標準測量誤差(standard error of measurement, SEM)與最小可偵測改變值(minimal detectable change, MDC)作為指標。所有測試皆採仰臥並且在腹部肌群放鬆之姿勢下接受測量。有關腹直肌厚度之測量位置分別為上、中、下三個位置。結果：兩位初學施測者針對各個肌群在不同位置肌肉厚度之ICC值≧0.77(0.77-0.96)呈現高信度、標準測量誤差在0.03-0.07之間、最小可偵測改變值在0.09-0.21之間。有關腹部各肌群在不同位置厚度之比較結果如下：腹直肌(1.01±0.17~1.10±0.22cm)與腹橫肌(0.31±0.08~0.36±0.09)在中間位置最薄，而上與下兩個位置厚度相同(p<0.05)；腹外斜肌(0.39±0.11~0.54±0.11cm)在中間位置最厚(p<0.05)、上與下兩個位置厚度相同；腹內斜肌(0.62±0.17~0.72±0.22)則是中間與下面兩個位置厚度相同但比上面位置厚(p<0.05)。各個位置之相對厚度大小順序依序皆為腹直肌、腹內斜肌、腹外斜肌與腹橫肌。結論：本研究結果發現年輕健康女性每條腹部肌肉在腹部上、中、下區域不同位置之肌肉厚度不同，但都是兩側對稱。另外，本研究結果也顯示初學者在操作超音波測量腹部各肌群之施測者間信度良好。區床意義：建議物理治療師可以使用超音波來測量不同部位與不同腹部肌群的厚度，以作為女性接受評估或治療之效果測量工具。

Background and Purpose: Little is known about the sizes of abdominal muscles at upper, middle, and lower regions. The prime purpose of this study was to evaluate the thickness, using ultrasound imaging, and symmetry of the abdominal muscles bilaterally at rest in healthy young women. The secondary purpose was to compare three locations at upper, middle and lower abdominal regions for assessing muscle thickness of rectus abdominis (RA), external oblique (EO), internal oblique (IO), transversus abdominis (TA). In addition, the inter-rater reliability was determined when these measurements taken by two novice raters. Methods: Thirty healthy female volunteers with mean age 20.6±1.9 years were recruited in this study. The ultrasound images of abdominal muscles of right and left sides were obtained with a 7.5 MHz, 40-mm linear array at a relaxed lying position. Thickness of RA, EO, IO, and TA at three locations (upper, middle. and lower) were measured. A repeated measures reliability study was conducted by two novice raters. Two raters received a standardized training program before obtaining measurements. Side-to-side differences in thickness of all abdominal muscles were assessed with paired-t tests, Intra-class correlation coefficient (ICC2.2), standard error of measurement (SEM), and the minimal detectable change (MDC) were used to establish the repeated measures reproducibility. Repeated-measures ANOVAs were used to test the differences in thickness among the muscles or locations. Results: There was no significant difference in thickness between both sides for all abdominal muscles. ICC2.2 were ranged from 0.77 to 0.96, indicating excellent inter-rater reliability. The SEM ranged from 0.03 to 0.07 cm, and the MDC ranged from 0.09 to 0.21 cm. Thickness of RA (1.01±0.17~1.10±0.22cm) and TA (0.31±0.08~0.36±0.09cm) was smaller at middle than the other locations; thickness of EO (0.39±0.11~0.54±0.11cm) was larger at middle than the other locations; thickness of IO (0.62±0.l7~0.72±0.22cm) was smaller at upper than the other locations. The pattern of descending order of muscle thickness was RA>IO>EO>TA. Conclusions: These findings support bilateral symmetry but different sizes of the RA, EO, IO, and TA at three locations at rest in healthy young females. Excellent reliability was obtained for all abdominal measures when taken by two novice raters. Clinical Relevance: Thickness measurements using ultrasound imaging may be applicable as a tool for both assessment and intervention in young female adults on continued research.