Transient pain and discomfort when wearing high-heeled shoes

In the dynamic world of fashion, high-heeled footwear is revered as a symbol of style, luxury and sophistication. Yet, beneath the facade of elegance of classy footwear lies the harsh reality of discomfort and pain. Thus, this study aims to investigate the influence of wearing high-heeled shoes on the sensation of pain across different body regions over a period of 6 h. It involved fifty female participants, all habitual wearers of high-heeled shoes, aged between 20 and 30 years. Each participant kept a record of their perceptions of pain and discomfort every hour for a total of 6 h using a 0–10 pain scale with 0 indicating no pain and 10 indicating severe pain. The findings reveal a progressive rise in pain throughout wear, with the most intense pain reported in the back, calcaneus, and metatarsals. The analysis shows that after approximately 3.5 h, participants experience significant increases in pain levels. However, the relationship between heel height and pain is not linear. It appears that a heel height of 7.5 cm is the threshold where overall body pain becomes significant. The study suggests that a duration of 3.5 h of wear and a heel height of 7.5 cm serve as critical points to decrease overall body pain. Moreover, beyond this heel height, knee pain diminishes compared to other body areas possibly due to the shift towards a more neutral posture. The study findings, coupled with the recommendations, can assist footwear designers in crafting not only stylish but also comfortable shoes.


Participants
Fifty female participants aged 20-30 years were instructed to record their experiences when wearing high-heeled shoes, detailing the areas and the severity of pain during the period March-April 2023.Each participant provided written informed consent to participate in the study.The demographic characteristics of the study participants are presented in Table 1.To mitigate the influence of pre-existing conditions, the study exclusively enrolled females who did not have any foot disorders or abnormalities, postural instability, spinal or knee issues, or a history of surgeries.Foot anatomy, anthropometry or fitness levels were not assessed.

Procedure
The evaluations were sought to determine whether pain levels increased across the entire body as the duration of shoe-wearing extended.To enhance the clarity of the survey process for the participants, the researcher showed an example where she donned high-heeled shoes with a height of 11.2 cm (Appendix C).A modified version of the pain assessment scale 49 (Fig. 1) was used to assess the extent of discomfort/pain experienced across various body regions during a 6-h duration.The form helped illustrate the experience using visual depictions of the pain locations, accompanied by pain intensity ratings and descriptions of the experimenter.
Each participant was tasked with wearing their uncomfortable high-heeled shoes for 6 h, adhering to the steps as demonstrated and explained by the researcher in the self-conducted survey (Appendix C).Throughout the 6-h duration, all participants performed their typical activities including sitting, standing, and walking on diverse surfaces.Such a procedure was intentional so that there is a realistic representation of daily life, avoided artificial constraints, has statistical randomness and enhanced generalizability.Subsequently, each study participant filled out the form provided to them (Appendix B), offering feedback on their individual experiences when wearing high-heeled shoes.

Results
The participant responses were summarized with descriptive statistics.The heel height worn by participants varied from 6.4 to 11.3 cm.To avoid single-point data, the heel heights were grouped into 0.5 cm intervals.Figure 2 displays the body part discomfort severity (BPDS) 50 across the entire body for different heel heights.
The BPDS was calculated as follows: Figure 2 shows that there is little to no pain (scale value of less than 1), up to a heel height of approximately 7.5 cm.Beyond this point, there is a gradual increase in reported pain with increasing heel height.Given this trend, further analysis was performed examining participants wearing heel heights below 7.5 cm and those at or above 7.5 cm.
In relation to the duration of wearing high-heeled shoes, mild discomfort becomes noticeable (at or above level 1) after approximately 3.5 h of wear when considering all the different body parts as a whole (i.e., mean of all ratings) (Fig. 3).The variation in the severity of pain over time in the various body parts is shown in Fig. 4 while the variation over heel height is shown in Fig. 5.The heel heights shown are the mid-point of the corresponding range of heel height.For example, the category linked with 6-6.5 cm is presented as 6.25 cm, aiming to streamline and enhance the clarity for identifying patterns, particularly in the context of using a bar chart.Figure 4 illustrates that back pain starts to develop after wearing high-heels for about 2.25 h while the pain in other parts of the body starts after around 3 h.
Due to the consistent pain patterns observed in the different parts of the body (Figs. 4 and 5), a correlation analysis (Table 2) was performed.The correlations reveal a consistent trend: pain levels increase across all areas of the body over time.However, there seems to be no such observable trend concerning heel height.The total body pain remained below 1 (indicating an absence of pain) for heel heights under 7.5 cm (Fig. 2).In light of this finding, a multiple regression analysis was done, using heel height and duration of wear as predictive factors.This analysis was performed separately for heel heights below 7.5 cm and those at or above 7.5 cm.This division was made considering the apparent threshold at 7.5 cm, beyond which pain becomes noticeable (Fig. 2).
The corresponding models and their coefficients are given in Table 3.The p-values for the related Time of wearing coefficients are less than 0.05 for all body parts.The regression coefficients of heel height show statistical significance at a 1% level for all body parts, except the ankle, toes, and leg.This suggests that heel height influences the pain levels in the shoulder, back, thigh, knee, metatarsals, and calcaneus.www.nature.com/scientificreports/coefficients express the hypothesized positive indications for heel height and duration of wear across all examined body regions when the heel height is under 7.5 cm.This suggests that an increase in these factors correlates with higher reported pain levels in the specified body areas.With regression coefficients of 0.76, for example, maintaining other variables constant, an increase of 1.3 cm in heel height is projected to correspond to a 1-point rise in back pain on a scale from 1 to 10.Similarly, each additional 2-h interval of wearing high-heeled shoes tends to raise the level of back pain by approximately 1-point as the regression coefficient is 0.5.For heel heights below 7.5 cm, the heel height coefficients have p-values that are less than 0.05 for all body parts except for the ankle, leg and toes, where the relevant p-values are 0.09, 0.33, and 0.53 respectively.For 7.5 cm or above heel heights, the p-values are less than 0.05 for all body parts except for the ankle, leg, toes, metatarsals, thigh and buttocks where the p-values are 0.82, 0.29, 0.58, 0.18, 0.26 and 0.74 respectively (Shown in italics in Table 3).Table 3 also includes R 2 values to indicate the goodness-of-fit for each regression model.The models for calcaneus pain (below 7.5 cm) and for back (at or above 7.5 cm) have the highest R 2 (0.60 and 0.75 respectively).
Based on the regression equation from Table 3, the predicted pain is plotted for a time duration of 0-8 h and a heel height of 6-15 cm (Fig. 6).In Fig. 6, the pain heat map color range is up to a pain level of 7 to indicate severe pain.The white rectangle within each plot indicates the experimental data region.We have shown the color plot beyond the regions tested to give a better overall picture of the pain realms.

Discussion
The pain levels experienced by 50 participants wearing high-heeled shoes for 6-h was evaluated.They assessed their pain on the shoulder, back, pelvis, thigh, knee, leg, ankle, toes, metatarsals, and calcaneus using a pain scale ranging from 0 to 10.Consistent with existing literature 10,[13][14][15] , it is seen that the higher the heel, the greater the pain experienced when wearing high-heeled shoes.The pain experienced by subjects appear to be due to two main causes: excessive pressure and muscle fatigue.The bony prominence pain is likely due to excessive pressure 16 and other location pain is most likely due to muscle fatigue.The back, metatarsals, and calcaneus experience the most amount of pain when wearing high-heeled shoes.Extended use of high heel shoes is also known to increase midfoot pain 25,32 .The reduced support, as a result of poor footbed designs, results in heightened foot pressure, particularly on the metatarsal heads, leading to changes in the center of pressure (COP) [18][19][20][21][22][23][24][25][26] .www.nature.com/scientificreports/Correlation and regression analysis show that there is a significant relationship between heel height, duration of wear, and subjective pain levels in various body parts among high-heel shoe wearers.Also, heel heights smaller than 7.5 cm seem to be the necessary heel height to avoid pain.Our findings do support Baaklini et al. 43 who claimed 4-7 cm heel heights do not affect comfort.Our data shows that pain is below level 1 up to heel heights of 7.5 cm.Mild pain (at or above a level of 1 on the pain scale) starts at around 7.5 cm of heel height.Our findings are in partial agreement with Lee et al. 41 asserting that 55% of people they surveyed had issues with a heel height of 6-9 cm.We hypothesize that the remaining 45% who do not experience any pain could be in the heel height range of 6-7.5 cm.Pain levels keep increasing as heel height increases, the reduction in pain level beyond 10.5 cm is not statistically significant (p > 0.05).The reduction could be due to a small sample size or another possibility is that those high heels are well designed to conform to body dynamics through a better match of COM and COP, which can be judged by an expert high-heel wearer at time of purchase.One important result based on this research is the change in sign of knee pain from positive to negative below 7.5 cm and above 7.5 cm heel height (Table 3).For the low heel heights knee pain increases with heel height but then switches sign beyond 7.5 cm.This is because, at higher heel heights, the knee is likely in a fully extended or neutral posture reducing any pain or discomfort to account for balance through postural adaptations.
Despite earlier research consistently highlighting the negative impacts of high-heeled shoes, they continue to grow in popularity among women as a fashion essential [1][2][3][4] .Contrary to popular belief, this research shows that there is a threshold time of wearing for high-heels to become painful.Beyond 3.5 h of wearing, there appears to be mild pain when considering the whole body.The reasons may be related to the time of adaptation and musclefatigue related time as reported in the literature where individuals alter their center of mass (COM) in relation to the center of pressure (COP) 33,34 through structural adjustments such as trunk and pelvis rotations 10,35,36 to modifications in muscle-tendon architecture [36][37][38] .According to the data, mild pain starts in the back after about 2 h followed by pain in the calcaneus, metatarsals and the toes (Fig. 4).Beyond 3.5 h, there is a rapid increase in pain in almost every part of the body part.This hypothesis needs further investigation.But, the key point here is the alteration of the COM with respect to COP.Instead, if COP is designed to match COM then the shoe would be a good design, and pain and discomfort can be reduced, if not eliminated.Figure 7 shows potential variations of the mismatch between COM and COP.If the COP is anterior to COM, then there will be an anticlockwise moment that has to be counteracted through shoulder movement or a clockwise rotation of the pelvis increasing the lumbar lordosis.If the COP is posterior to the COM, then the opposite will happen and there will be a decrease in lumbar lordosis.This explanation agrees with the published literature where some have shown an increased lumbar lordosis [40][41][42] , some others decreased lordosis and kyphosis 43 , and the rest have shown no significant impact on lumbar lordosis 44,45 .After about 3.5 h of wearing, there seems to be some adaptation to shift the COM to the back of the foot to relieve the pain on the toes as there is sharp increase in the level of pain in the calcaneus and the metatarsals whereas there is only a slow increase of pain in the toes (Fig. 4).This adaptation seems to rotate the pelvis and thus we see an increase in pain in the leg and buttocks.High-heels will have no impact on lumbar lordosis when the COM variations are small and "match" the COP through appropriate footbed design by manipulating the wedge angle and shank shape [51][52][53] .Designing the footbed right the first time is the key to minimizing fatigue, discomfort, and pain.
Given the significant debate surrounding high-heels and their connection to pain or discomfort, it is also necessary to examine the "other factors" influencing high heels as highlighted by Baaklini et al. 43 .The heel height might not be the most crucial parameter that should be explored.It could be the shape of the footbed that influences posture, pain, discomfort, and stability because the support surface has a direct bearing on the center of pressure (COP) and the COP-COM mismatch 51 .The findings stress the importance of considering footwear characteristics to minimize discomfort and pain.Individuals should be aware of the potential consequences of wearing high heels for extended periods and choose footwear that balances style with comfort to reduce the risk of pain and discomfort.
There are several limitations in this study.Firstly, despite a total of 50 participants, the sample size within each heel height group was relatively small.Moreover, participants wore their own shoes, which were not standardized across the study, introducing some variability.Additionally, factors like BMI and foot sizes were not controlled, potentially impacting lower limb forces, particularly on different walking surfaces, and subsequently influencing foot-shoe interface pressures.However, these wide variations, inherent in the cross-sectional design, afford a more comprehensive understanding of real-life scenarios and enable the capture of diverse results, including COP COM www.nature.com/scientificreports/those pertaining to time and heel height.Nonetheless, it is apparent that larger studies, incorporating greater control over potential variations of various factors, are warranted to address the aforementioned issues effectively.

Conclusions
The study data and analysis reveal compelling trends concerning high-heeled shoe wear.Even in the most uncomfortable shoes, participants can wear them for about 3.5 h, after which pain levels consistently increase.The body areas most affected are the back, metatarsals, and the calcaneus.With "other" factors constant, an increase of 1.3 cm in heel height is estimated to correspond to a 1-point increase in back pain on a 1-10 scale.Similarly, for every additional 2-h increment of high-heeled shoe wear, back pain tends to increase by approximately 1-point.Additionally, it is observed that a heel height of up to 7.5 cm imposes a tolerable level of discomfort or pain compared to heights exceeding 7.5 cm.Discrepancies between the Center of Mass (COM) and Center of Pressure (COP) may be the primary contributors to explain the variations in the existing literature.While the COM can fluctuate with bodily adaptations, the COP can be altered through footbed design.Further research is necessary to test the proposed hypotheses to bring cohesion to the existing body of literature.

Figure 1 .Figure 2 .Figure 3 .
Figure2shows that there is little to no pain (scale value of less than 1), up to a heel height of approximately 7.5 cm.Beyond this point, there is a gradual increase in reported pain with increasing heel height.Given this trend, further analysis was performed examining participants wearing heel heights below 7.5 cm and those at or above 7.5 cm.In relation to the duration of wearing high-heeled shoes, mild discomfort becomes noticeable (at or above level 1) after approximately 3.5 h of wear when considering all the different body parts as a whole (i.e., mean of all ratings) (Fig.3).The variation in the severity of pain over time in the various body parts is shown in Fig.4while the variation over heel height is shown in Fig.5.The heel heights shown are the mid-point of the corresponding range of heel height.For example, the category linked with 6-6.5 cm is presented as 6.25 cm, aiming to streamline and enhance the clarity for identifying patterns, particularly in the context of using a bar chart.Figure4illustrates that back pain starts to develop after wearing high-heels for about 2.25 h while the pain in other parts of the body starts after around 3 h.Due to the consistent pain patterns observed in the different parts of the body (Figs.4 and 5), a correlation analysis (Table2) was performed.The correlations reveal a consistent trend: pain levels increase across all areas of the body over time.However, there seems to be no such observable trend concerning heel height.The total body pain remained below 1 (indicating an absence of pain) for heel heights under 7.5 cm (Fig.2).In light of this finding, a multiple regression analysis was done, using heel height and duration of wear as predictive factors.This analysis was performed separately for heel heights below 7.5 cm and those at or above 7.5 cm.This division was made considering the apparent threshold at 7.5 cm, beyond which pain becomes noticeable (Fig.2).The corresponding models and their coefficients are given in Table3.The p-values for the related Time of wearing coefficients are less than 0.05 for all body parts.The regression coefficients of heel height show statistical significance at a 1% level for all body parts, except the ankle, toes, and leg.This suggests that heel height influences the pain levels in the shoulder, back, thigh, knee, metatarsals, and calcaneus.The findings also indicate that all

Figure 4 .
Figure 4. Mean level of pain over time on various body parts.

Figure 5 .
Figure 5. Mean level of pain of the various body parts when wearing differing heel heights of shoes.

Figure 6 .
Figure 6.Pain heat maps for different body parts.The color range is up to a pain level of 7 to indicate severe pain.All predicted negative pain values have been set to zero.The light-white rectangle within each plot indicates the region tested in experiment.

Figure 7 .
Figure 7. COP is anterior to COM.

Table 2 .
Correlation coefficients between heel height, time and pain level.Coefficients 0.65 or greater are in italics.Coefficients 0.5 or greater are in bold.

Table 3 .
Regression coefficients of Body Pain on Heel Height and duration of use.The top line corresponds to a heel height below 7.5 cm.The values for heel heights 7.5 cm or above are in parenthesis.The regression coefficients in italics are those having p-values above 0.05.Vol:.(1234567890)Scientific Reports | (2024) 14:9291 | https://doi.org/10.1038/s41598-024-59966-9