尝思古圣以背为阳。腹为阴。先贤以背为阴。腹为阳。岂前后有异。而上下不同欤。然愚谓以体之刚柔言。
则背阳而腹阴。以用之动静言。则背阴而腹阳。且阳化气。阴成形。是腹背皆可谓之阴。阳在外。阴在内。是
腹背皆可谓之阳。阴阳之道。其大无外。其小无内。岂特一端而已哉。夫背者。胸中之府。其中行乃督脉之
所行。其第二行挟脊各一寸半。第三行挟脊各三寸者。太阳之所行也。其经脉自上而下。则部位有上下
之分。其疾病或左或右。则部位有左右之辨。推而言之。身半以上为阳。身半以下为阴。左为阳。右为阴。皮
肤在外为阳。筋骨在内为阴。是故上下标本不同。左右逆从亦异。诊之之法。可不精求其理哉。言乎其形。
则肿起者。邪气实。陷下者。正气虚。背高如龟曰龟背。脊骨如锯曰脊疳。背烂透膜者。形坏岂能治。背平病
水者。肺伤不可疗。此形之因病而变者。言乎其容。则脊强者。病在太阳。反折者。病在督脉。背曲肩随者。胸
中之府将坏。项强腰折者。背上之经已伤。颈直背强。称身回侧者。肝实之状。骨枯髓减。腰脊不举者。骨痿
之形。呼吸摇肩者。心中坚。转摇不能者。肾将惫。诸反张。大人脊容侧手。小儿脊容三指者。不可治。此容之
因病而变者。于是合气色以观其同异。参脉症而辨其本标。将虚中有实。实中有虚。虽变化无穷。而意见
有定。庶几其各当欤。且凡言实者。邪气实也。言虚者。正气虚也。邪气实者。正气有有余不足。正气虚者。邪
气有有余不足。一切精微法。应作如是观。非惟诊背宜尔也。
我曾思考，古代圣人认为背部属阳，腹部属阴。而先贤则认为背部属阴，腹部属阳。难道是因为身体前后位置不同，或者上下部位有别吗？然而我认为，从形体的刚柔角度来看，背部为阳而腹部为阴；从功能的动静角度来看，背部为阴而腹部为阳。况且，“阳”具有化生气的功能，“阴”具有形成形的作用，因此腹和背都可以被称为阴（指其有形之质）；“阳”在外护卫，“阴”在内守藏，因此腹和背也都可以被称为阳（指其功能之气）。阴阳的道理，广大无边无际，细微无内可寻，岂止是单一方面的含义呢？
背部，是胸中脏腑的外府。背部正中线是督脉（总督一身之阳经的经脉）所行的部位；背部第二行线距离脊柱旁开一寸半处，第三行线距离脊柱旁开三寸处，是足太阳膀胱经（足太阳经）所行的部位。其经脉自上而下行走，所以部位有上下的区分；其疾病或出现在左侧或右侧，所以部位有左右的辨别。推而言之，身体上半部分属阳，下半部分属阴；左侧属阳，右侧属阴；皮肤在表属阳，筋骨在里属阴。因此，上下标本不同，左右逆从也有差异。诊察的方法，怎能不精密地探求其中的道理呢？
从形体变化来看，肿胀突起的是邪气实盛，凹陷下陷的是正气虚弱。背部高耸像乌龟一样叫作“龟背”，脊骨突出像锯子一样叫作“脊疳”（一种以脊骨畸形为主的虚损病证）。背部溃烂穿透膜层的，形体败坏，怎么能治疗呢？背部平坦且患有水肿病的，说明肺脏受损，不可治愈。这是形体因疾病而产生的变化。
从姿态容态来看，脊背僵硬强直，病位在足太阳经；身体向后反折（角弓反张），病位在督脉。背部弯曲、肩膀下垂随顺，说明胸中之府即将败坏。颈部强直、腰部折断，说明背部的经络已经受伤。颈部挺直、背部强硬，身体歪斜侧倾，这是肝气实盛的征象。骨骼枯槁、骨髓减少、腰脊不能抬举，这是骨痿（骨骼萎弱无力）的形态。呼吸时耸动肩膀，说明心部坚实（邪结于心）；身体转动摇晃不能自如，说明肾脏即将衰竭。各种反张拘急的症状，成人背部侧面能容纳一只手，小儿背部侧面能容纳三根手指的，属于不可治愈的危候。这是姿态因疾病而产生的变化。
于是，结合气色来观察其异同，参考脉象和症状来辨别本标虚实。即使是虚中有实、实中有虚，虽然病情变化无穷，但诊断的意见要有定见，这样才能大致恰当吧。而且，凡是说“实”的，是指邪气实盛；凡是说“虚”的，是指正气虚弱。邪气实盛时，正气可能有有余或不足的情况；正气虚弱时，邪气可能有有余或不足的情况。一切精微的诊断法则，都应这样看待。这不仅适用于诊察背部，其他部位也是如此。
I have pondered that the ancient sages considered the back to be Yang and the abdomen to be Yin. However, earlier experts considered the back to be Yin and the abdomen to be Yang. Is it because of differences between the anterior and posterior aspects, or variations between upper and lower regions? Yet, I believe that from the perspective of the physical structure's rigidity and flexibility, the back is Yang and the abdomen is Yin. From the perspective of function's movement and stillness, the back is Yin and the abdomen is Yang. Furthermore, "Yang" transforms into Qi (vital energy), while "Yin" forms into substance. Thus, both the abdomen and back can be referred to as Yin (referring to their substantial nature). "Yang" resides on the exterior for protection, while "Yin" resides within for storage; thus, both the abdomen and back can also be referred to as Yang (referring to their functional aspect). The Dao of Yin and Yang is vast with no external limit and subtle with no internal boundary; how can it be limited to a single aspect?
The back is the outer mansion of the chest organs. The midline of the back is the pathway of the Du Mai (Governor Vessel, which controls all Yang meridians). The second line, located 1.5 cun lateral to the spine, and the third line, located 3 cun lateral to the spine, are the pathways of the Foot-Taiyang Bladder Meridian (Zu Taiyang Jing). As these meridians descend from above, there are distinctions in upper and lower locations. Since diseases may occur on either the left or right side, there are distinctions in left and right locations. Extending this reasoning, the upper half of the body is Yang, and the lower half is Yin; the left side is Yang, and the right side is Yin; the skin on the exterior is Yang, and the sinews and bones on the interior are Yin. Therefore, the upper and lower biao and ben (branch and root) differ, and the left and right ni and cong (reverse and compliant) also vary. How can the methods of diagnosis fail to meticulously seek the underlying principles?
Regarding morphological changes: swelling and protrusion indicate excess of pathogenic factors (Xie Qi); depression and sinking indicate deficiency of healthy Qi (Zheng Qi). A back elevated like a turtle is called "Gui Bei" (Turtle Back); a spine protruding like a saw is called "Ji Gan" (Spine Rickets/Atrophy). If the back ulcerates and penetrates the membranes, the form is ruined and cannot be treated. If the back is flat and accompanied by edema, the Lung is damaged and cannot be cured. These are changes in form due to disease.
Regarding postural manifestations: stiffness of the spine indicates pathology in the Foot-Taiyang Meridian; opisthotonos (backward arching) indicates pathology in the Du Mai. A curved back with drooping shoulders suggests the imminent collapse of the chest mansion. Neck stiffness with lumbar flexion indicates injury to the meridians of the back. A straight neck with stiff back, accompanied by a tilted and leaning body, is a sign of Liver Excess. Withered bones and depleted marrow, with an inability to lift the waist and spine, constitute the form of Gu Wei (Bone Flaccidity). Shoulders rising during respiration indicates firmness in the Heart region; inability to turn or sway indicates impending exhaustion of the Kidney. For various cases of opisthotonos, if the lateral aspect of an adult's back can accommodate a hand, or that of a child can accommodate three fingers, the condition is incurable. These are changes in posture due to disease.
Therefore, one must combine observation of complexion to discern similarities and differences, and reference pulse and symptoms to differentiate root and branch, deficiency and excess. Although conditions such as deficiency containing excess or excess containing deficiency may change infinitely, diagnostic judgment must remain fixed, so that treatment may be appropriate. Generally, when we speak of "Excess," we refer to the excess of pathogenic factors; when we speak of "Deficiency," we refer to the deficiency of healthy Qi. When pathogenic factors are excessive, healthy Qi may be either in surplus or deficit; when healthy Qi is deficient, pathogenic factors may be either in surplus or deficit. All subtle diagnostic laws should be viewed in this manner. This applies not only to diagnosing the back but to all areas.