Excessive Weight Bearing Compromises Foot Structure and Function Across the Lifespan - The Mechanobiology of Obesity and Related Diseases - page 144

1 Introduction
Feet are highly unique and flexible structures composed of 26 bones and 33 joints
that are required to perform extremely diverse functions throughout everyday tasks
[ 1 ]. As the body's base of support and terminal link in the lower extremity kinetic
chain during both stance and dynamic gait, feet must oppose the effect of weight-
bearing forces on the human body when performing activities of daily living, work
and recreation. For this reason, an individual's feet must continually endure the
often-high ground reaction forces generated during these activities. Structurally
and functionally sound feet endure this loading with only minor, if any, apparent
discomfort. Should normal foot development or lower limb alignment be
compromised, however, more permanent and debilitating conditions of the feet
may result.
Obesity is one of these debilitating conditions that, in children, negatively
impacts foot structure and function. Structurally, the feet of obese children, com-
pared to non-obese children, are broader, flatter and rounder. Functionally, obese
children generate significantly higher dynamic pressures beneath their feet during
walking than do normal weight children. Similar compromises in foot structure and
function are also evident in both young and older adults. As compromised foot
structure associated with obesity is a potential deterrent to participation in physical
activity, and thus perpetuates the cycle of obesity, it is deemed a major health issue
that requires immediate intervention. In this chapter, we review the effects of
bearing excessive body mass on foot structure and function across a lifespan. Where
possible, we highlight the impact of this excessive weight bearing on the ability of
individuals to perform activities of daily living.
2 Development of the Foot
As children grow their foot structure also develops. The foot of an infant usually
appears to be flat because the typical arched nature of the medial foot margin is not
yet apparent (Fig. 1 ). This occurs primarily due to the presence of fat padding
beneath the developing medial longitudinal arch, which remains to protect this
vulnerable region of the paediatric foot as load bearing begins [ 2 ]. As body mass is
gained with age, the tensile strength of the ligamentous and muscular structures of
the foot also increases. After 1 year of independent walking, an advancing
indentation on the medial aspect of a child's footprint can be seen [ 2 ]. Around the
age of 3 years, ossification of the navicular occurs [ 3 ] and a mature gait pattern is
established [ 4 ]. This longitudinal arch development is thought to be due to skeletal
changes within the foot, in combination with a reduction of the fat pad underneath
the arch, which is resolved between the ages of 5 and 8 years [ 5 ]. Following this
developmental process, the child's foot takes on characteristics of an adult foot,
with a defined longitudinal arch. Although young children's feet grow rapidly,