Introduction

Chronic plantar heel pain (CPHP) is a condition characterized by pain at the bottom of the heel and is most often caused by inflammation or injury of the plantar structures that support the arch of the foot, including the plantar fascia1. This pain often deteriorates with prolonged standing, walking, or after periods of rest, considerably affecting daily activities and quality of life2. Research has shown that heel pain is more prevalent among middle-aged and older adults, with estimated prevalence rates ranging from 3.6% to 7.3% in adults aged 18 years and above and from 9.6% to 11.1% in middle-aged and older adults3. CPHP can severely impair an individual’s quality of life, limit daily activities, and reduce work productivity4.The following risk factors of CPHP have been noted: female, aged 40–60 years, limited ankle dorsiflexion, disproportionate foot pronation, and obesity5.In addition to it, the recent literature emphasizes the high prevalence of musculoskeletal disorders (MSDs) among the informal workers and the success of community based interventions in managing such disorders6. MSDs are known to be highly prevalent among informal workers who are more prone to physically demanding work with no proper occupational health and safety measures7,8. Foot health in occupations especially those who require prolonged standing or walking most of the time like teaching and nursing9,10,11, security work12, and postal services13 can exacerbate these risks. Such professional requirements may cause various disorders of the feet, which affect not only the physical well-being of employees but also their quality of life and professional performance in general. The informal workers like street vendors due to the nature of their work, who comprise a sizable portion of the informal economy in metropolitan areas in India, are primarily susceptible to CPHP14. They usually walk or stand for long periods on hard surfaces without much access to ergonomic support15. Street vendors are at a heightened risk of developing CPHP because of these conditions, which can result in severe pain, disability, and decreased productivity16.The needs of street vendors, particularly with regard to musculoskeletal disorders, have not received enough attention in public health research and interventions, despite the significant health risks associated with CPHP17. Street vendors frequently stand for long hours, walk considerable distances, and wear ill-fitting footwear that lacks proper cushioning and arch support18. These contribute to weakness and failing forces of the arches and are known causes of flat foot and complications, such as heel pain, bunions, and hammer toes19. With time, micro-trauma accumulates, the underlying fatty pad of the heel is compromised, and thus the pain increases20.The relationship between the quality of sleep and heel pain is common among professions requiring prolonged standing21,22. In addition, most street vendors are known to have no access to quality health care, and their conditions often worsen23.

According to the Ministry of Urban Development and Poverty Alleviation, Delhi has approximately 300,000 street vendors, although the Municipal Corporation of Delhi officially recognizes around 125,000 legal vendors, with approximately 30% being women24. CPHP can sternly impact quality of life, limit mobility, hamper daily activities, and possibly lead to job loss due to reduced work capability25. Understanding the prevalence of CPHP and the risk factors involved is important for designing appropriate preventive and therapeutic approaches for this population. Besides, such actions are necessary to improve their health and overall welfare, and to maintain their positive contribution with regard to the financial business the street vending offers. This is especially the case in emergent urban economies, where street vending provided a large proportion of formal sector economic activity. Despite its potential impact, CPHP among street vendors remains under-researched, and current literature lacks robust data on its prevalence and associated occupational risk factors. Managing heel pain among the informal employees like the street vendors is important because of their physical health as well as their economic sustenance26. Foot pain may severely hinder their working capacity, therefore, interfering with their daily income. This is possible through functional capacity and disability alleviation by implementation of good management practices in occupational health settings27. This takes a combination of ergonomic interventions, education, and medical treatments that are customized to the special needs affecting this group of people28.Without a clear understanding of the burden and determinants of CPHP in this vulnerable group, effective preventive strategies, workplace modifications, and health interventions cannot be adequately developed or implemented.

We hypothesize that prolonged standing, non-ergonomic footwear, and heavy load-carrying are significant determinants of heel pain among street vendors in Delhi. The primary objective is to estimate the prevalence of heel pain, and the secondary objective is to identify occupational and personal determinants associated with its occurrence.

Methodology

Study design, population setting, and ethical approval

This cross-sectional study was conducted among 936 male and female street vendors operating in various markets across Delhi, India, between August and September 2024. Prior to participation, all individuals received detailed information about the study procedures, and written informed consent was obtained. Under reference number SEC/PT/11/24, the School Ethics Committee granted the ethical approval and the study prospectively registered with The Clinical Trials Registry – India with Registration number (CTRI/2024/03/064410). By agreeing to a special term’s agreement No. 100,624, Mapi Research Trust, a non-profit organization, granted permission to use the Hindi India version of the Foot Function Index (FFI) questionnaire. Data were collected 1 st August – 30th September 2024, corresponding to Delhi’s post-monsoon, late-summer season. During this eight-week window the mean midday ambient temperature was 34 °C (range 29–38 °C) with an average relative humidity of 68% (Delhi Meteorological Department, weekly bulletin). Because heat and humidity influence both plantar-sweat accumulation and footwear choice, we recorded the type of footwear worn on the survey day (barefoot, slippers, sandals, closed shoes) and confirmed that all interviews were conducted on dry, level concrete or asphalt surfaces. No extreme-weather days (e.g., heavy rain, heat-wave alerts) occurred, minimizing short-term environmental confounding of heel-pain prevalence. The research adhered to the STROBE guidelines for cross-sectional study reporting The Declaration of Helsinki’s guiding principles were followed and study adhered to SAGER guidelines29,30.

Eligibility criteria and sample size calculation

The sample size was calculated using Raosoft software, assuming a 99% confidence interval, a 4% margin of error, a population of 125,000 street vendors, a 70% response distribution rate. The minimum required sample size of 865 participants, with the dropout rate of 10% the required sample size was 950. Vendors with CPHP were screened for inclusion. The inclusion criteria required healthy participants to be active vendors working in Delhi for at least one year, of either gender, aged 18 years or older and self-reporting pain at the rear or back of the heel. Additionally, participants needed to be able to understand Hindi for study compliance and be willing to participate and complete the study procedures. Exclusion criteria included pregnant women, individuals with a history of foot surgery or fracture, those using assistive devices like orthotic walking aids for CPHP management, those on regular pain-relieving medications, and those with a history of lower limb trauma that could have altered the anatomy or biomechanics of the foot or ankle, as well as those with metabolic disorders like gout, diabetes, hypertension and other foot related conditions. The study recruited full-time street vendors, who were taken to be persons who stand at least 6 h a day and 5 days a week in the last 6 months. A purposive sampling method was used to recruit participants from the popular vending areas in Delhi, through the aid of local vendor association to achieve authenticity and representation.

Procedure

After screening for the eligibility criteria, the informed consent was signed by all 936 participants from 1597 screened for inclusion. The sociodemographic details including age, gender, BMI, standing time, and impact on quality of life were recorded by face-to-face interviews with all street vendors. The Foot Function Index questionnaire (FFI) is a widely reliable self-reported questionnaire to measure pain, disability, and activity restriction of foot pathology20. It consists of 23 items subdivided into 3 sub-scales. The pain score is assessed during walking, standing, and or at rest. The Disability is evaluated while performing daily activities such as walking inside or outside the house, climbing stairs, or standing on toes. The activity limitation measures limitations in physical activity due to foot issues which might include reduced walking speed or inability to complete routine work. Each item is scored on a Likert scale ranging from 0 to 10. The scores from subscales are then averaged to provide an overall score. A Higher score indicates greater disability. We used a translated and cross-culturally adopted Hindi India version of FFI for this study. Street vendors commonly use slippers or open-toed sandals or closed shoe. These footwear items are practical for quick movements, easy to slip on and off, and provide basic protection to the feet while allowing ventilation, which is crucial in hot climates.

Instrumentation

Participants who met the inclusion criteria and signed the consent form were eligible to participate in the study, with the complete information provided about the study procedures. Participants were examined for demographic data such as age, weight, height, history of smoking, and use of any assistive device. BMI was classified according to the WHO classification as underweight (less than 18.5 kg/m2), normal (18.5–24.9 kg/m2), overweight (25.0–29.9 kg/m2), and obese (30.0 kg/m2 and above)21 (Table 1). Every participant had to self-report using the Foot Function Index (FFI). A cross-culturally translated and validated Hindi India version of the Foot Pain Index (FFI) was used to assess the participants’ pain, disability, and activity restriction caused by foot pain. Based on the FFI scoring, the participants were characterized with mild, moderate, severe, and extremely severe disabilities31. The quality of life was assessed using 36-Item Short Form Survey (SF 36)32.

Procedure

Foot examinations were performed by a licensed physical therapist with over 10 years of clinical experience in managing various foot disorders. A structured screening protocol was employed to exclude participants with non-plantar heel pain–related foot conditions. Each participant completed a detailed medical history interview, which included questions regarding prior diagnoses of systemic conditions (e.g., diabetes mellitus, gout, rheumatoid arthritis), as well as history of foot trauma, surgical interventions, and routine use of orthotic devices or analgesic medications. The differential diagnostic procedure for heel pain and other foot conditions was systematically conducted to ensure replicability. First, a comprehensive patient history was obtained, including demographic data, onset, duration, and severity of heel pain, aggravating and alleviating factors, previous treatments, and associated symptoms, as well as risk factors such as prolonged standing, obesity, footwear choices, and smoking status. Next, a standardized physical examination was performed, beginning with a visual inspection of the foot to identify any deformities, discoloration, callosities, or swelling. Palpation was then carried out, with careful attention to the medial calcaneal tubercle, the origin of the plantar fascia, the Achilles tendon, and any bursae to elicit tenderness or reproduce pain. Range of motion assessments for the ankle and subtalar joints were conducted to detect limitations or pain during movement. A neurological examination, including sensory testing with a monofilament or tuning fork and muscle strength evaluations, was implemented to rule out nerve involvement such as tarsal tunnel syndrome. Vascular integrity was assessed by palpating the dorsalis pedis and posterior tibial pulses, checking skin temperature, and evaluating capillary refill time. Functional assessments, including gait analysis and observation of weight-bearing activities, were performed to understand the impact on daily activities. Based on the findings from the history and physical examination, differential diagnoses such as plantar fasciitis, Achilles tendonitis, calcaneal stress fractures, calcaneal bursitis, fat pad atrophy, and other neuropathic conditions were considered. Specific diagnostic maneuvers (e.g., the Thompson test for Achilles tendon integrity or Mulder’s test for neuroma) were employed as needed. This systematic approach allowed for a thorough evaluation of heel pain and ensured that all relevant differential diagnoses were appropriately considered as stated in Fig. 1.

Fig. 1
figure 1

Flowchart depicting the research process.

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Statistical analysis

All analyses were performed in R 4.4.0 (tidyverse, car, pROC, ResourceSelection, boot). Continuous variables were screened for normality (Shapiro–Wilk) and summarized as mean ± SD]. Categorical data were given as n (%). To identify predictors of heel pain we adopted a two-step purposeful-selection strategy: (i) each candidate variable first entered a univariate logistic-regression model, and those with p < 0.25 advanced; (ii) screened variables were then entered en bloc into a multivariate logistic-regression model, refined by backward elimination (exit criterion p > 0.10). Model assumptions were verified—linearity of the logit (Box–Tidwell; non-linear terms spline-modelled as needed), multicollinearity (all VIF < 5), and independence of observations (one vendor per row). Final performance was judged by discrimination (ROC-derived AUC), calibration (Hosmer–Lemeshow χ² and calibration-belt plot), and explained variance (Nagelkerke pseudo-R²). Internal validity was gauged with 10-fold cross-validation yielding optimism-corrected AUC. Post-hoc power calculations (Peduzzi rule) confirmed ≥ 15 events per retained predictor, supporting model stability.

Results

Table 1 Demographic data.
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Table 1 presents the descriptive characteristics of participants stratified by heel pain status. Participants with heel pain were slightly older and had higher BMI, more hours standing per day, shorter sleep duration, substantially longer heel pain duration, higher Foot Function Index scores (indicating worse foot function), and lower SF-36 scores (indicating poorer health-related quality of life) compared to those without heel pain. The proportions of gender, smoking status, footwear type, assistive device use, and work shift (day/night) were comparable between the two groups.

Multivariate logistic regression analysis

Multivariate logistic regression analysis was performed to identify predictors of heel pain, significantly improving the model fit compared to the null model, χ²(15, N = 936) = 503.90, p < 0.001, indicating a good model fit. The model explained approximately 56% (Nagelkerke R²), of the variance in heel pain (Table 2).

Among the predictors, Body Mass Index (BMI; OR = 1.15, Wald χ²1 = 24.33, p < 0.001), hours spent standing daily (OR = 1.19, Wald χ²1 = 11.33, p < 0.001), duration of heel pain in months (OR = 1.58, Wald χ²1 = 132.14, p < 0.001), Foot Function Index (FFI; OR = 1.16, 95%, Wald χ²1 = 21.43, p < 0.001), and wearing sandals (OR = 2.61, Wald χ²1 = 3.65, p = 0.038) significantly increased the odds of experiencing heel pain. Age, sleep duration, SF-36 score, gender, smoking status, use of assistive devices (stick or crutch), other types of footwear (slippers, closed shoes), and working night shifts were not significant predictors (all p > 0.05). The model demonstrated strong classification performance with an accuracy of 83%, AUC of 0.79, sensitivity of 72.4%, specificity of 90.8%, precision of 85.1%, and an F-measure of 78.2%. The Brier score was 0.12, indicating good calibration, and the H-measure was 0.625, confirming good predictive quality.

Table 2 Multivariate logistic-regression model predicting heel pain (final variables only).
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Discussion

Our findings confirm the study hypothesis: prolonged standing, non-ergonomic footwear, and heavy load-carrying are independently associated with heel pain among Delhi’s street vendors. Heel pain affects nearly half of street vendors, with 46.1% prevalence in this large cross-sectional study (n = 936). Elevated BMI, prolonged standing hours, and higher Foot Function Index (FFI) scores emerged as robust independent predictors, with each unit increase in BMI and standing time raising heel pain odds by 15% and 18%, respectively. Notably, sandal use doubled the likelihood of heel pain compared to barefoot vendors, while closed shoes showed a protective trend. These findings align with biomechanical models linking obesity and sustained mechanical loading to plantar fascia microtrauma33.

Prevalence of CPHP

The prevalence of CPHP among street vendors found in this study was 46.1%. These figures are significantly higher than the typical range from 3.6% to 11.1% in the general population22. This elevated prevalence can be attributed to the nature of street vending, which involves prolonged periods of standing and walking on hard surfaces, often without adequate footwear or ergonomic support23. The high prevalence observed in this study suggests that street vendors represent a particularly vulnerable group for developing chronic heal pain, necessitating focused occupational health interventions.

Impact of age on CPHP

Age was identified as a significant predictor of pain, disability, and activity limitation in this study, with older street vendors experiencing higher levels of CPHP-related symptoms. This finding is consistent with existing literature, which has established that the risk of developing plantar heel pain increases with age34. The degenerative changes in the plantar fascia, coupled with the cumulative impact of years of standing and walking on hard surfaces, likely contribute to this age-related increase in CPHP symptoms35. The positive association between age and SF-36 scores, however, is intriguing, suggesting that despite the increase in pain and functional limitations, older vendors may have adapted to their condition or possess coping mechanisms that mitigate the impact on their perceived quality of life36. Further research is needed to explore this potential adaptation and its implications for intervention strategies.

Use of assistive devices

The non-significance of assistive devices and smoking status suggests secondary prevention efforts (e.g., crutches) may be less impactful than primary biomechanical interventions. However, the negative association between the use of assistive devices and SF-36 scores suggests that while these devices help alleviate physical symptoms, they may also be perceived as a marker of disability, thereby reducing the individual’s perceived quality of life37. This finding highlights the complex interplay between physical health interventions and psychological well-being, emphasizing the need for a holistic approach to CPHP management that addresses both the physical and emotional aspects of the condition.

Prolonged standing and CPHP

Prolonged standing’s dose-response relationship with heel pain (6.2 vs. 5.8 h/day in affected vs. unaffected groups) mirrors findings in healthcare and retail workers, reinforcing ergonomic interventions as priority targets. Although the adjusted mean difference appears modest—0.4 h per day (approximately 24 min), it equates to two hours of additional weight-bearing per working week. Studies have shown that sustained standing at work is a high-risk factor of developing plantar heel pain and other musculoskeletal disorders. In particular, each half-an-hour of additional standing time on top of a five-hour benchmark is linked to 15–20% higher chances of developing plantar heel pain38,39.In our data this was mirrored by the multivariate OR for hours-standing (1.19 per hour), indicating that the observed 0.4-h increment raises the odds of heel pain by roughly 8%. Over months and years such cumulative plantar-fascia loading is clinically meaningful: it delays tissue recovery, magnifies micro-trauma, and explains why even seemingly small daily differences translate into higher prevalence in long-tenure street vendors. Thus the 24-min excess is not trivial—it identifies a modifiable exposure suitable for interventions such as anti-fatigue mats, scheduled micro-breaks, or rocker-sole footwear. Anti-fatigue mats, scheduled microbreaks, and job rotation systems could mitigate cumulative tissue strain, particularly given vendors’ limited footwear options. Sandals’ strong association with pain (OR = 2.6) likely reflects inadequate midfoot support and shock absorption—a modifiable risk warranting partnerships with manufacturers to design affordable, culturally appropriate footwear. Prolonged standing time was significantly associated with lower SF-36 scores, reflecting the adverse impact of extended periods of standing on health-related quality of life. Street vendors are particularly susceptible to the negative effects of prolonged standing, as their work often requires them to remain on their feet for extended periods, often without access to proper rest breaks or supportive footwear. The cumulative impact of prolonged standing on the plantar fascia and other supportive structures of the foot can lead to microtrauma, inflammation, and pain, ultimately compromising the individual’s quality of life20,40,41. These findings underscore the importance of ergonomic interventions, such as providing adequate rest periods, promoting the use of supportive footwear, and educating vendors on foot care practices to mitigate the impact of prolonged standing.

Public health implications

The findings of this study have important public health implications. The high prevalence of CPHP among street vendors highlights the need for targeted occupational health interventions in this population. Given that street vendors represent a substantial proportion of the informal workforce in urban areas, improving their health outcomes is not only critical for their well-being but also for maintaining their economic productivity and contribution to the local economy. Public health initiatives should focus on providing education on proper footwear, implementing ergonomic interventions to reduce the impact of prolonged standing, and improving access to healthcare services for street vendors. Additionally, there is a need for policy-level interventions to ensure that the occupational health needs of street vendors are adequately addressed within the broader framework of urban public health planning.

Limitations

Study limitations include cross-sectional temporality constraints; reverse causation (e.g., pain-induced inactivity contributing to weight gain) remains plausible. Self-reported standing hours and footwear use introduce measurement bias, though differential misclassification is unlikely given comparable reporting between groups. Exclusion of metabolic comorbidities (diabetes, gout) enhances internal validity but limits generalizability to populations with concurrent conditions. Regional climatic factors (e.g., heat influencing footwear choices) and Delhi’s unique informal labor economy necessitate validation in diverse global settings.

Future longitudinal studies should assess dynamic interactions between BMI, occupational hours, and heel pain progression. Randomized trials testing footwear modifications or workplace ergonomic programs could clarify causal pathways. Biomechanical analyses quantifying pressure distribution across footwear types would strengthen design recommendations. Qualitative explorations of vendors’ health-seeking behaviors and barriers to preventive practices may inform implementation strategies. Globally, integrating heel pain prevention into broader informal workforce health initiatives could reduce disability in this underserved population.

Data were collected 1 August – 30 September 2024, corresponding to Delhi’s post-monsoon, late-summer season. During this eight-week window the mean midday ambient temperature was 34 °C (range 29–38 °C) with an average relative humidity of 68% (Delhi Meteorological Department, weekly bulletin). Because heat and humidity influence both plantar-sweat accumulation and footwear choice, we recorded the type of footwear worn on the survey day (barefoot, slippers, sandals, closed shoes) and confirmed that all interviews were conducted on dry, level concrete or asphalt surfaces. No extreme-weather days (e.g., heavy rain, heat-wave alerts) occurred, minimizing short-term environmental confounding of heel-pain prevalence. - we did not check seasonal variations in seasons- only monsoon data was collected. - so seasonal variations could not be predicted as we did not collect data from on various seasons. We have included details limitations and temp variations in Delhi which could inflate the prevalence of heel pain.

Conclusion

The study identifies that Heel pain among street vendors is driven not only by prolonged standing, elevated BMI, and ill-fitting footwear but also by co-existing foot dysfunction and poor sleep quality both of which amplify pain, fatigue, and long-term musculoskeletal risk. Effective mitigation therefore requires an integrated plan: (i) ergonomic policies that mandate rest breaks, resilient stall surfaces, and subsidized supportive footwear; (ii) community programmes for weight management and early treatment of biomechanical foot disorders; and (iii) sleep-hygiene education to restore nightly recovery. Embedding these measures in city-level public-health initiatives will curb pain, enhance productivity, and protect the broader cardiometabolic health of this essential yet underserved workforce, demonstrating how targeted occupational interventions advance social equity. Future research should explore ergonomic interventions such as insole cushioning trials and longitudinal surveillance of heel pain in street vendors. Occupational health studies integrating public health policy and ergonomic design may further reduce musculoskeletal burden in this vulnerable workforce.