The relationship between the body mass index (BMI) and foot posture in elderly people

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Abstract

We wanted to evaluate the postural characteristics of the feet of older people and their relationship with the BMI. We evaluated 227 older women and 172 older men with respect to the BMI, the arch index (AI) and the foot posture index (FPI). The obese women presented mean values for the AI significantly greater than those of the normal and overweight women. The means for some of the criteria of the FPI were significantly higher in the obese men. There was a positive correlation between the BMI and the AI and some of the FPI criteria. The conclusion was that obese women presented flatter feet while obese men presented more pronated feet, indicating a relationship between high BMI values and postural characteristics of the feet of subjects studied.

Introduction

In the third age, after years of use, the feet of older people may present a characteristic aspect, since the tissue changes occurring due to senescence are capable of altering the foot morphology (Finlay, 1995). Such structural changes can result in modification in foot dynamics, resulting in specific overloads which cause repetitive stress injury (Hunter et al., 1995). There is evidence suggesting a causal relationship between the arch structure, musculoskeletal performance and injuries (Saltzman et al., 1995).

The flatfoot, often associated with valgism of the calcaneum and with forefoot abduction (Ananthakrisnan et al., 1999, Silveira, 1999), is intimately associated with ligament laxity and obesity (Sachithanandam and Benjamin, 1995). Some studies have also indicated a high correlation between flat feet and dysfunctions of the tibialis-posterior muscle (Kohls-Gatzoulis et al., 2004, Karges, 2005). The cavus foot presents a smaller plantar area (Silveira, 1999) and greater overload on the lateral plantar surface of the foot (Hunter et al., 1995).

One of the ways of evaluating the plantar arch is from the footprints, which offer greater intra- and inter-observer reliability than the clinical anthropometric evaluations (Saltzman et al., 1995), as well as being an easily accessible and cheap technique (Kanatli et al., 2001). Some authors, such as Cavanagh and Rodgers (1987) and Staheli et al. (1987), created indexes capable of classifying the foot according to the height of the arch. The AI, described by Cavanagh and Rodgers (1987) has already been validated for older people.

Alignment deviations, including pronation and supination, may be evaluated using the FPI, which takes into consideration the following six criteria: talar head palpation, supra- and inframalleolar curvature, calcaneal frontal plane position, prominence in the region of the talo-navicular joint, congruence of the medial longitudinal arch and abduction/adduction of the forefoot on the rearfoot (Redmond et al., 2006). This index has also been validated for older people.

In addition to structural changes due to aging, obesity is an important factor to be considered in the morphology of the elderly foot. Tavares and Anjos (1999), analyzing data from older people aged 60 years or above in Brazil, registered an obesity prevalence of 5.7% in men and 18.2% in women.

The BMI defined as the individual's body weight divided by the square of his height (kg/m2), is a useful measurement to evaluate the excess of body fat (Pinheiro et al., 2004). The World Health Organization defines BMI values between 18.5 and 24.9 as normal; values below 18.5 as underweight and values over 30 as obese (WHO, 1997). Many studies criticize the cut-off values of the BMI because they do not take into account the sex, age range and the distinction between lean body mass (muscles) and fat body mass (adipose tissue) (Anjos, 1992, Da Cruz et al., 2004, Pinheiro et al., 2004). One argument used to demonstrate the inadequacy of the BMI with respect to the different age ranges is that many transformations occur with aging, indicating the use of anthropometry in the evaluation of obesity in the elderly, since they present higher tolerance to the morbid-mortality associated with the increase in BMI. This could justify defining obesity with a higher BMI threshold in this stage of life (Stevens, 2000). Nevertheless, BMI can be a strong predictor of health problems associated with obesity (Da Cruz et al., 2004).

The elucidation of a possible relationship between obesity and postural changes in the feet of older people is important in the search for preventive or palliative strategies that aim to improve the quality of life of this population.

Section snippets

Methods

Individuals aged 60 years and over, of both sexes and resident in the City of São Carlos, SP, Brazil, took part in this study. Older people with any form of lower amputations, or were using first aid dressings or orthoses that impeded direct contact of the instruments with the skin, were excluded from this study. The sample was determined considering the elderly population of the city of São Carlos, according to the proportions of gender and age groups found there. Thus the sample was

Results

The female sample presented a mean BMI of 28.45 ± 5.12 kg/m2, and the male sample of 27.0 ± 4.24 kg/m2. Table 1 shows the percentages of women and men in each of the BMI groups.

Table 2, Table 3 present the results of the Pearson's correlation as applied to the AI and FPI in the female and male groups, respectively. In the female group, the BMI maintained a low positive correlation with the AI of the left feet, and a moderately positive correlation with the AI of the right feet. In the women there was

Discussion

The results indicate higher prevalence of obesity in older women when compared to men in the same age range. This has already been demonstrated by many authors who cite, besides the predominance of obesity in the female sex, an association between this and risk factors like hypertension, diabetes and sedentarism (Barreto et al., 2003, Santos and Sichieri, 2005).

In the women, a negative correlation was found between the BMI and the second FPI criterion, indicating that obese women presented more

Conflict of interest statement

None.

Acknowledgement

The authors are grateful to the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP, Brazil) for its financial support.

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