At a postural level, many doctors, physiotherapists and chiropractors are convinced that lower back pain induced by heels is due to an increase in lumbar lordosis associated with an anterior pelvic tilt; this thought is even shared by the American Chiropractic Association and the American Physical Therapy Association.

Furthermore, in most of the websites consulted, even by non-experts, the reason for the onset of spinal pain is attributed to hyperlordosis and pelvic anteversion. However, this thought is not entirely in agreement with other scientific publications. Therefore it is necessary to pay attention to online searches which often answer these questions without taking EBM into account.

None of the studies reported above take into consideration the time factor. In fact, all the studies have evaluated the immediate changes brought about by heel raising. Women who complain of lower back pain when wearing high-heeled shoes rarely experience pain as soon as they start wearing them.

The objective of the research arises from these considerations. The aim of this study (primary outcome) is to investigate whether wearing high-heeled shoes for at least 2 hours modifies the spinopelvic parameters compared to the barefoot condition and as soon as the shoes are worn.

The secondary outcome will be to verify in the sample analyzed whether there are different behaviors between the subgroups of those who have complained in their anamnesis and those who have never complained of lower back pain when using high-heeled shoes for a few hours.

A three-dimensional analysis of the posterior surface will be performed with the Formetric 4D® rasterstereographic device (Diers International GmbH, Schlangenbad, Germany).

Participants will be given a questionnaire which investigates:

• Age, weight, height of the participants;
• Any pain in the spine (measured by NPS) usually reported by subjects after using high-heeled shoes;
• Type of profession;
• Frequency with which the subjects wear the heeled shoe (how many hours per week);
• Heel height of the shoe with which they participate in the clinical study;
• Any spinal pain (measured by NPS) after wearing heeled footwear for the study period.

This last data will be filled in at the end of the evaluation.

For the evaluation of the secondary outcome, on the basis of the data from the medical history sheet, the sample will be divided into two groups:

1. The first group (group A, ASYMPTOMATIC) includes subjects who during daily life do not report spinal pain after wearing high-heeled shoes;
2. The second group (group S, SYMPTOMATIC) is made up of participants who usually complain of more or less intense pain after using the shoe.

The subjects will be asked to bring their own pair of shoes with a heel that is at least 8.7 cm, the average height reported by the work of Schroeder and Hollander, where average height means the difference between the height of the heel and the height of the raised part at the forefoot level (plateau). A particular heel width will not be required, because it seems that the height of the heel influences muscle activation, in particular the paravertebral muscles, while the width of the heel has no significant effects on them.

Conversely, amplitude has a greater influence on balance when standing and while walking.

Three evaluation will be performed:

1. first evaluation in neutral position with bare feet (T0)
2. second evaluation in neutral position wearing shoes (T1);
3. third evaluation like the previous one but at least 2 hours apart, in which it will be required to remain standing still or walk (T2).

Statistic analysis

A descriptive analysis of the population will be performed to determine the mean values and standard deviations (SD) of both the combined group and the subgroups A and S. T-tests for independent data will be used to verify whether there are any significant differences between the two subgroups .

The distribution of the data will be verified using graphical representation. If the distribution is normal (p <0.05) for the comparison between T1 vs T2 the t-test for paired data will be used and between the subgroups (T1S vs T1A and T2S vs T2A) t-test for independent data with statistical significance accepted for p values <0.05. ANOVA will be used to simultaneously compare the pre and post of both groups.

If the data does not have a normal distribution (p >0.05) the Wilcoxon test will be used for the comparison between the T1 vs T2 data of the total group and the Mann-Whitney U test for the comparison between subgroups (T1S vs T1A and T2S vs T2A). The Friedman test will be used to simultaneously compare the pre and post of both groups.

Inclusion Criteria:

• female subjects aged between 20 and 40 years
• Usual users of shoes with heels at least 7 cm high, with a frequency of at least twice a week and/or less than 3 hours/week

Exclusion Criteria:

• structural or neurological anomalies that may prevent you from remaining weight-bearing, for approximately 2 hours, with shoes having a heel (difference between the heel and the plateau) of at least 7 cm high;

Usual female users of shoes with heels at least 7 cm high, with a frequency of at least twice a week and/or less than 3 hours/week