A relation between dynamic strength and manual materials-handling strategy affected by knowledge of strength

Objective: We studied the relation between dynamic (isokinetic) strength and the batch-assorting strategy to initiate a manual materials-handling task and the effect of knowledge of strength on that relation. Background: The debated, complex relationship between muscular strength and the risk of injury can be better understood from a behavioral perspective by examining performance strategies in physical acts such as lifting. Methods: Thirty-two participants (16 men and 16 women) were first tested for their isokinetic strengths of trunk extension, knee extension, shoulder extension, and shoulder abduction. The participants were then divided into two groups, one provided with knowledge feedback of their strength testing results and the other not provided with such feedback. Participants subsequently performed the same load-handling task in which they carried batches of various weight plates while allowed to assort batches of more than one plate into any combination. Results: Dynamic strength, as represented by a total isokinetic strength score, and knowledge feedback both had significant effects on measures quantifying the batch-assorting strategy. Conclusion: Individuals with greater strength tended to adopt a strategy corresponding to a heavier load per carry and fewer carries per batch. Receiving knowledge feedback evoked a tendency toward handling a heavier load, and this tendency was more salient in the weaker individuals. Application: Potential applications include the use of strength testing in worker selection and training as well as in job design to promote better strategies of balancing productivity and injury prevention.