Asthenia and sthenia are two principles to differentiate the conditions of healthy qi and pathogenic factors. Asthenia refers to insufficiency of healthy qi, while sthenia refers to exuberance of pathogenic factors. Syndrome differentiation of asthenia and sthenia is helpful for understanding whether pathogenic factors are in predominance or decline so as to decide to select therapy for complementing asthenia and strengthening healthy qi or therapy for purging sthenia and eliminating pathogenic factors.

Asthenia syndrome  
Asthenia syndrome refers to symptoms marked by asthenia of healthy qi and non-predomination of pathogenic factors. The cause of asthenia syndrome is either congenital or postnatal, especially the postnatal one. The postnatal cause include insufficiency of qi and blood production due to improper diet, impairment of visceral qi and blood due to emotional factors and overstrain, exhaustion of renal essence due to excessive coitus, or impairment of healthy qi due to chronic disease, etc.

Clinical manifestations:
Healthy qi in the human body mainly includes yangqi, yin fluid, essence, blood and body fluid, all of which are closely related to the viscera. Therefore, asthenia syndrome is mainly marked by insufficiency of yangqi, yin fluid, essence, blood and body fluid as well as the decline of visceral functions. The clinical manifestations of asthenia syndrome vary with different types which will be explained in the following parts. Here the common symptoms are taken as example to analyze the clinical manifestations of asthenia syndrome. The common symptoms include fatigue, shortness of breath, no desire to speak, aversion to cold and cold limbs, spontaneous sweating, clear and profuse urine, loose stool, emaciation,? feverish sensation over the five centers (palms, soles and chest), tidal fever, flushed cheeks, night sweating, pale or sallow complexion, dizziness, palpitation and insomnia, dry mouth and throat, thirst with desire to drink, dry skin, scanty urine and dry feces, tender tongue with thin fur or little fur and weak pulse, etc.

Analysis of symptoms:
Fatigue, shortness of breath and no desire to speak are due to failure of asthenic yangqi to propel and nourish the body, leading to hypofunction of viscera and tissues; spontaneous sweating is caused by? failure of deficiency of yangqi and failure of defensive qi to guard the superficies; clear and profuse urine and loose stool are due to failure of deficient yang to astringe, warm and transport; emaciation is due to failure of deficient yin to nourish the body; feverish sensation over the five centers, tidal fever and flushed cheeks are due to predominance of yang heat, internal generation of asthenic heat and yin asthenia failing to control yang.

Night sweating is due to asthenic heat driving body fluid to be excreted; pale or sallow complexion is due to blood asthenia failing to nourish the face; dizziness is due to blood asthenia failing to nourish the head and eyes; palpitation is due to malnutrition of the heart; insomnia is due to blood asthenia failing to nourish heart spirit; dry mouth, desire to drink and dry skin are due to failure of deficient fluid to nourish and moisten the tissues and organs; scanty urine is due to deficiency of body fluid and insufficiency of body fluid production; dry feces is due to loss of lubrication in the large intestine; tender tongue, thin fur or little fur and weak pulse are signs of deficiency of healthy qi.

Sthenia syndrome  
Sthenia syndrome refers to symptoms of predominant pathogenic factors and non-asthenic healthy qi. The cause of sthenia syndrome includes two factors: one is invasion of exogenous pathogenic factors into the body; the other is dysfunction of the viscera, leading to the accumulation of phlegm, fluid, dampness and blood stasis in the body.

Clinical manifestations:
The clinical manifestations vary with different types of sthenia syndrome due to the difference of pathogenic factors and the invading and accumulating regions. For example, internal predominance of?pathogenic cold manifests cold syndrome, while exuberance of pathogenic heat manifests sthenic heat syndrome. The internal sthenic syndromes due to internal exuberance of phlegm, fluid, dampness, blood stasis and retention of food also vary in clinical manifestations which will be discussed in the following sections. Here the common symptoms are taken as examples to show the characteristics of sthenia syndrome. The common symptoms include fever, restlessness, even coma with delirium, chest oppression, hoarse breath, exuberance of phlegm and drool, impalpable pain of abdomen, retention of dry feces, or dysentery with blood and pus, tenesmus, inhibited urination, or?painful stranguria, tough tongue, thick or greasy fur and sthenic pulse, etc.

Analysis of symptoms:
Fever is due to exuberant pathogenic factors, confliction between healthy qi and pathogenic factors and predomination of yang heat; restlessness is due to pathogenic heat disturbing the heart; coma with delirium is due to exuberant heat disturbing heart spirit or sthenic pathogenic factors confusing heart spirit; chest oppression, hoarse breath and profuse sputum with rale are due to retention of pathogenic factors in the lung which prevents the lung from dispersing and descending; retention of feces and impalpable abdominal pain are due to accumulation of sthenic pathogenic factors in the stomach and intestines which prevents free flow of intestinal qi.

Dysentery with blood and pus and tenesmus are due to accumulation of damp heat in the large intestine which hinders the transportation of the large intestine; inhibited urination is due to retention of fluid and dampness and inhibited transformation of qi; painful stranguria is due to accumulation of damp heat in the bladder and inhibited transformation of qi in the bladder; tough tongue with thick or greasy fur and sthenic pulse are the signs of internal retention of pathogenic factors and confliction between healthy qi and pathogenic factors.