The uniformity of results described in this paper can be explained by a anatomophysiological factor common to humans, the rectoanal angle, which is straightened with hip flexing.

The angle between the rectum and the anal canal varies from one individual to another (graded 64– 134) (3) and is a major factor in continence for solid rectal content (4). In his radiological study, Tagart showed that the rectoanal angle straightens with fully flexed hips—corresponding to the squatting position assumed for defecation—and converts the rectoanal outlet into a straight canal, thereby facilitating rectal emptying (5).

The results of the present study are in excellent agreement with this line of thinking and may be summarized as follows: the greater the hip flexion, the straighter the rectoanal canal and, accordingly, the less strain required emptying the bowels.

The only deviation from this rule in the present study cohort was seen in the six volunteers (Subjects 7, 11, 16, 23, 24, and 28) who had reported more straining for emptying the rectum while sitting on the lower toilet seat. It can be speculated that hip flexion, which is usually greater in this posture than when seated on a regular toilet seat, was not sufficient to straighten the rectoanal canal and reduce the straining in these subjects while the unusual position of sitting on a toilet seat 31– 32 cm high had a strong influence on these volunteers’ expressing the need for more straining than they had required while sitting on a regular toilet seat.

The attempt to achieve more straining reduction in sitting posture by even more reduction of height of toilet seat and accordingly more hip flexing was not successful. As noted above, four consecutive volunteers refused to defecate on a toilet seat 26–27 cm high because of unacceptable discomfort. All volunteers, independently of variables such as diet, length of feces evacuation, age, height, weight, and sex, needed significantly less time for feces evacuation in the squatting posture than in any sitting posture.

This phenomenon, characteristic of 100% of volunteers, excludes the possibility that the additional time spent on defecation in the sitting posture is an innocent factor lacking any significance. Moreover, in sitting postures, the volunteers spent on average 1.9–2.1 min to empty the rectum. It is too short a time for reading the paper or just sitting, but it is too long compared with the 0.85 min spent on sensation of satisfactory bowel emptying in squatting posture. The extra time spent in the sitting posture is necessary for excessive straining in order to push the feces through almost right rectoanal angle, while in the squatting posture significantly less straining is necessary as the feces are pushing out along the open outlet due to straightening of the rectoanal junction.

The above arguments are in agreement with the volunteers’ subjective assessment, which determined defecation is “very easy” in 44% in the squatting posture, while this was as in 9–20% in the sitting postures (Table 2), generally assessing the sitting postures 2–2.5 time more difficult than the squatting posture (Figure 2).

From elementary mechanics it is well known that any system exposed to excessive pressures ultimately sustains injury (6). Historically, man has squatted in order to defecate (7), and the practice continues today in underdeveloped countries (8). The widespread use of a sitting toilet in the Western world began during the 19th century when sewage systems were developed to improve sanitation as cities grew (9). In the middle of the 20th century, a group of physicians working in rural Africa were surprised by the near absence of hemorrhoids, constipation, hiatus hernia, and diverticulosis coli in rural black populations (10). They further found that the rarity of these problems is also characteristic for other underdeveloped countries.

Those authors attributed this finding to a high fiber diet, and studies were embarked upon to confirm this hypothesis with regard to diverticulosis coli. Following this and other publications, the Western world has taken steps to enrich their diets with edible fibers, but the prevalence of the abovementioned diseases has not changed. Moreover, several later studies on the role of low fiber diet in the etiology of diverticulosis coli could not confirm such associations (11–13).

The results of the present study can well explain the findings of Burkitt et al (10) of specific geographic distributions of the diseases mentioned: individuals residing in geographical areas with a high prevalence of these problems characteristically use sitting toilets while a low prevalence is found in areas where people characteristically use squatting toilets.

The defecation act results from a chain of events known as Valsalva maneuver and when protracted and repeated may case cardiac rhythm disturbances (14, 15), reduction of coronary (16) and cerebral (17) blood flow explaining defecation syncope and death (14, 17, 18).

The brief defecation effort in the squatting posture, as shown in this study, may prevent many cardiovascular events. In conclusion, the present study, together with the earlier data in the literature, point to the far greater expulsive effort needed for defection while seated as a being the causative factor of several medical problems.