Can Relative Strength Between the Back and Knees Differentiate Lifting Strategy?

Abstract

Objective: This study investigated whether relative strength between the back and knees can differentiate and predict lifting strategy and the effects of gender, load magnitude, and knowledge of strength on the strategy. Background: Although muscular strength is thought to play a vital role in the mechanics of lifting, how localized joint strengths and their relations influence lifting strategy remains unclear. Method: Thirty-two participants (16 men and 16 women) underwent isokinetic strength tests and were then divided into two groups: one provided with the knowledge of their strength test results and the other not. They subsequently performed the same set of simulated lifting tasks while their lifting kinematics were being recorded. Postural indices to quantify the lifting strategies were derived from the kinematic data. Results: The ratio of back strength versus total knee strength and gender had significant effects on measures quantifying the lifting strategy. A statistical model incorporating gender, strength, and anthropometry achieved an R2value of .64 and predicted correctly 76% of lifting strategies used by individual participants. Conclusion: Individuals with back strength greater than their total knee strength tended to use a back-preferred lift strategy, and vice versa, suggesting that muscular strength is a determining factor of lifting strategy. Application: An emphasis on additional knee strengthening in a training program may change the tendency of using and overstressing the back. Application of modeling and simulation technology for ergonomics design can be enhanced by more individually and accurately specified lifting strategies based on anthropometry and strength profiles.