BIOMECHANICS

THE BIOMECHANICS OF GAIT AND RUNNING

By Nat Padhiar

Although there is an increasing amount of evidence to support the benefits of sport and exercise to both physical and psycho- logical well-being the inevitable result of this increased participation is an increased risk of injury. Running is probably the most common form of exercise and this article will focus on the importance of biome- chanics and biomechanical factors respon- sible for running injuries.

Previous studies have divided risk into intrinsic and extrinsic factors related to injury (1,2).

Extrinsic factors include training habits, shoes and training surface while intrinsic factors include biomechanical components (ie. excessive pronation, malalignment , cavus feet, leg length discrepancy), age, somatotype, previous history of injury and physical fitness.

Extrinsic factors ● Footwear ● Weather ● Terrain

● Training surface

Intrinsic factors ● Age and sex

● Height, weight, BMI ● Previous injury ● Fitness

● Activity intensity ● Technique and skill ● Specific activity

● Psychological factors

● Biomechanical factors

Introduction The mechanical behaviour of the foot and ankle is an integral part of the function of the entire lower limb during ambulation. The lower limb works as an integrated functional unit, with each limb consisting of segments with specific capabilities and limitations. Knowledge of the characteris- tics of each limb segment is required in order to understand the mechanics of nor- mal gait and pathomechanics (pathologies relating to the mechanics) of injuries.

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The lever system of the long bones in the lower limbs is responsible for transmitting the body weight. This system must oper- ate through the foot structure which has the capacity to sustain these stresses dur- ing locomotion. The foot structure consists of a series of ‘jointed’ segments. The most important segments include the ankle, sub- talar and midtarsal joints. Individually each of these joints have three planes of motion with varying characteristics, collec- tively they allow the foot to adapt to dif- ferent types of terrain (ie.uneven, bumpy or sloped) or to compensate for changes in the positions of the superimposed body. This facility is known as ‘normal’ compen- sation and is an integral part of normal locomotion.

‘Normal’ relationships between body seg- ments are a pre-requisite for normal func- tion and any significant deviation in posi- tion, structure or function from average anatomical values, particularly in the lower limb may cause abnormal compensation. In the foot this usually means compensation by abnormal pronation or supination.

The literal definition of biomechanics is the study or application of mechanical laws relating to the movement or structure of living organisms.

Abnormal mechanics can cause ● Mistiming of joint motions in the gait cycle ● Altered angle of muscle action eg. tib- ialis posterior and achilles tendinitis, plan- tar fasciitis ● Misalignment of

joint eg. valgus ankle,

hallux valgus ● Reduced capacity to withstand forces acting on the part eg. stress fractures, rup- tures

Without intervention abnormal compensa- tion is likely to be permanent, repetitive and destructive (see tables 1 & 2).

‘Normal’ foot biomechanics Leonardo da Vinci who was an outstanding genius of the Renaissance and had under- standing of most sciences well beyond his time referred to the foot as ‘a masterpiece of engineering and a work of art’. The mod- ern day understanding of foot biomechan- ics and science is credited to the early pio- neering work of Hick (3) and Inman (4). In podiatry this is credited to Root, Weed, Sgarlato, Orien & Hughes (5,6) whose method of biomechanical examination of the foot is well documented and remains the most widely practised method in clini- cal podiatric biomechanics and surgery.

Gait analysis Assessment of gait and posture provides important information on the severity of the problem during the dynamic phase. This combined with static biomechanical examination provides an overall picture of the compensatory movements that occur as a result of mal-position.

The subtalar joint plays a crucial role in human locomotion. Subtalar joint pronation ‘unlocks’ the midtarsal joint, allowing the foot to become a mobile adaptor while subtalar joint supination ‘locks’ the midtarsal joint, allowing the foot to become a rigid lever.

Scientific analysis of the human gait improved in technique and experimental methods tremendously in the 20th century. This was not as a result of discovery, but by advancement of observation and experi- mentation of human movement over the centuries. In most podiatric clinics howev- er, observation still remains the mainstay technique in assessment of the gait cycle. In some cases video analysis with patients walking/running on a treadmill is utilised with the facility to analyse sections of the gait cycle frame by frame and in very slow motion. An understanding of the normal walking and running cycle (Fig.1) is vital.

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