Infantile faccidity syndrome occurs after epidemic febrile diseases in most children while it also may exist in some infantile patients immediately after birth. With the increase of age, the syndrome gradually worsens. The syndrome prevails at the age of 5 to 10, without obvious seasonal feature. Many causes give rise to flaccidity syndrome, the most common ones being consumption of body fluid due to pathogenic heat, invasion of dampness and heat, asthenia of the spleen and stomach as well as deficiency of the liver and kidney. It is generally believed that the syndrome like the one with sudden onset and short course accompanied by exterior symptoms such as chills and fever belong to sthenia syndrome in most cases.

Prolonged summer-heat and virulent heat pathogen scorch the lung while pulmonary heat consumes body fluid, making body fluid insufficient in distribution to all the body. In this case, the muscle will lose its nourishment, giving rise to flaccidity of feet or paralysis of limbs. Besides, dampness and heat stagnate and steam, spreading to muscle and tendons. On this occasion, qi and blood get stagnated, resuiting in flaccidity and weakness of feet. Slow onset, lingering course or progressive exacerbation mainly belong to asthenia or asthenia intermingled with sthenia in pathogenesis. The concurrent insufficiency and postnatal improper nursing in infantile patients cause asthenia of the spleen and stomach, giving rise to the shortage of the source for producing and transforming qi and blood. Besides, deficiency of the liver and kidney makes the muscle lose its nourishment. In these cases, flaccidity syndrome occurs.