An Ergonomic OH&S Analysis of Muscle Activation and Posture When Terra Firma Products are Utilised During Pit Lid Lifting and Replacing Operations.

Authors: Dr Kevin Netto, Mr Caleb Lewis, Mr Gavin Lenton, School of Exercise and Nutrition Sciences, Deakin University


Clear links can be seen between the OH&S risks for workers conducting manual handling activities and weight of the objects being handled as well as the frequency of lifting those objects.

As the weight of an object being moved increases the risk of injury to the worker also increases. The risk of injury is highest at the point when the muscles are under the most strain. This point is called peak muscle activation. Bending the body (trunk flexion) beyond 30° also increases risk of injury. Reduction in peak muscle activation and trunk flexion directly decreases the risk of injury in workers who lift and replace lids as part of their daily work tasks.

This study considered if a difference in pit cover weight could reduce manual handling stress and associated risk of injury. Terra Firma Industries manufacture composite pit covers and lifting keys. These lids are substantially lighter than conventional concrete or ductile iron lids however, the impacts of the weight and design of the lids and lifting tool on worker stress have not been measured. This study measured the differences in muscle activation and posture when a range of pit lids were lifted and replaced. The effect on muscle activation and posture of different lifting keys was also assessed.

Peak muscle activation stresses were measured using wireless electromyography to quantify muscle activation levels from the back (erector spinae) and the shoulder (trapezius) muscles. Trunk flexion was observed in the field via video and in the laboratory using a 12-camera motion analysis system.


Peak Muscle activation reductions of over 200% were seen when comparing Terra Firma products to traditional products. It can be estimated that injury risk is most probably reduced by up to 200 fold when using Terra Firma products. Furthermore, when considering the OH&S hierarchy of risk management, Terra Firma pit lids have achieved an optimal safety outcome by simply engineering risk out of handling pit covers.

Click here to download a full copy of the Deakin University OH&S Report

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