The Role of Walking Dynamics in Walking-Surface Safety

By: Ronald J. Cohen, P.E. and Andrés J. Calderón, Ph.D.

Engineers regulate the design, construction, and maintenance of walking-surfaces.  They consider the dynamics of walking to evaluate reasonably safe tolerances for the construction and maintenance of the built environment when evaluating walking use.  This evaluation includes the walking dynamics of pedestrians, such as walking speeds to determine limits for traffic light timing sequences at a roadway crossing, stepping movement for curb locations, stair ambulation, and walking stride, and gait measurements.  These dynamics are used to consider dimensional limitations in the built environment.  Obviously, this list can go on.  This is a civil engineering assessment.  A biomechanical engineering assessment can be more involved.  For instance, a biomechanical engineering walking analysis may include further considerations like a particular muscle or tendon or joint action, the skeletal-muscular forces that may be generated and evaluating a particular injury that may result from a specific movement or motion.

The following is an abbreviated understanding of the dynamics of walking used by engineers:

Explaining some basic terms:

Mass is an amount of matter.  Weight reflects the force of gravity acting on a mass.  Therefore, a person’s weight would be different on the moon where there is less gravity.  However, the person’s mass, whether on earth or on the moon, would remain constant.  For a standing person, the mass is centered in the torso and the centroid of the mass acts approximately through the navel. 

During walking, the rearward leg swings forward past the opposing stationary leg and stops ahead from the body to touch-down with heel strike.  Therefore, the opposing leg becomes the rearward leg. 

• Heel Strike Phase – The forward swung foot initially contacts the ground surface at heel strike and then the foot rotates downward to a flat position on the ground. 
• Flat Foot or Stance Phase – The forward flattened foot is weight bearing while the trunk/mass is moving forward during the swing phase. 
• Toe Off – The rearward foot lifts at the heel onto the ball of the foot and pushes off.  This is a rearward push, which aids in forward propulsion. 
• Swing Phase – The rearward foot swings forward, which follows a travel path along an arc.

• Low Toe Clearance – During the swing phase, as the foot travels forward the toe is pointed downward.  When the swinging leg moves forward and is approximately aligned with body the toe is at its lowest clearance from the walking-surface.

It should be understood, these dynamics of walking relate to normal ambulation for pedestrians without disability.  The following are Google Images demonstrating the dynamics of walking movement:

Consider these walking dynamics:

A trip usually occurs at low toe ground clearance.  The swinging foot’s forward travel is impeded at the toe by an on-ground obstruction and the leg is prevented or restricted from moving ahead to a position of balance and stability.  At the same time, the body mass is shifting forward, which results in a loss of equilibrium and control.  Sometimes a stumble step can be made, and balance may be restored. 

A slip can occur at forward foot heel strike when body mass is shifting to the forward foot and frictional resistance below the foot is insufficient to resist sliding, which is the required traction at heel strike.  Alternately, the rearward foot can slip backward at toe push off when frictional resistance below the foot is insufficient to resist sliding, which is the required traction at toe off.  The direction and movement of a falling person depends on the mechanics of the foot slide at the time of the slip.  A common heel strike slide would cause the person to fall backwards, and a push off slip often causes the person to fall in a split position. 

The built environment:

We walk in a built environment that includes certain imperfections related to the reasonable ability to construct and maintain walking-surfaces.  Therefore, engineers set tolerances for construction and maintenance of walking-surfaces.  These tolerances consider construction practices and material limitations in combination with walking dynamics.  They are reflected in engineering codes, standards, and practices.  Using this basis, the engineer evaluates the safety of a walking-surface to determine whether a specific condition of or on the property was a cause or factor in a walking related injury.  A biomechanical engineer can also determine if the claimed injury is consistent with the built environment and/or the description of the accident.

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