Comparative ergonomic analysis of different items of safety footwear in automotive manufacture

Status:

completed 12/2010

Aims:

Numerous workplaces exist in automotive manufacture which require tasks to be performed primarily standing or walking. These tasks are associated in some cases with complaints of the musculoskeletal system, particularly of the spine and the lower extremities.
The extent to which the safety footwear worn is responsible for the incidence of health complaints in the musculoskeletal system and can be used as a preventive measure for their minimization remains largely unclear. Studies of safety footwear conducted in the past examined local complaints in the foot region, and the prevention aspect primarily considered the avoidance of injury caused by occupational accidents.
The purpose of the present study was therefore to examine the influence of different designs of safety shoe upon the physical stress imposed upon the postural and locomotor apparatus. Its focus lay upon differences in the finishing of the safety footwear according to ergonomic requirements, for example shoe cushioning, fit and sole design.
The influence of different designs of work safety footwear upon the physical stresses imposed upon the postural and locomotor apparatus and the model of safety shoe which might potentially increase or reduce the stress upon the musculoskeletal system are aspects requiring examination.
The study was performed at the site of an automotive manufacturer in the course of a dissertation supervised by the Institute of Occupational Medicine at the RWTH Aachen and the Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA).

Activities/Methods:

The stress profiles of 40 test subjects in two different areas of activity within automotive production were studied by means of a CUELA measurement system specially adapted to the study problem. Three different safety footwear concepts (safety shoes 1, 2 and 3) were tested both in standardized measurements and in field measurements. The joint angle and foot pressure distribution were evaluated as the measurement parameters.
Parallel to the measurements, surveys were conducted of the subjective comfort and complaints.
Statistical analyses were used for comparative study of the different safety footwear concepts.

Results:

CUELA measurements revealed the influence of the safety footwear upon the body posture and the plantar pressure distribution. Walking and working in safety shoe 1 for example was characterized by greater forward inclination of the upper body and increased hip flexion. The different shoes were not found to differ in their influence upon the knee joint. Measurement of the plantar pressure distribution revealed a substantially higher pressure in safety shoe 1. In the hindfoot in particular, the maximum pressure values exceeded those of the comparison models by up to 37%. Analysis of the gait line parameter also revealed shoe-specific differences in the longitudinal and lateral deflection. Walking in safety shoe 3 was characterized by a shorter gait line and by a foot strike closer to the centre of the heel. With safety shoe 2, the gait line was characterized by a roll-over movement closer to the outer edge of the foot.
The subjective impression of the test subjects, who ranked safety shoe 1 worse than the comparison models, was consistent with the measured values. Altogether, a measurement method was developed which can be used for comparative ergonomic analysis of safety footwear.

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