The Stoop-Squat-Index: a simple but powerful measure for quantifying lifting behavior

TL;DR

The paper introduces the Stoop-Squat-Index, a simple measure to quantify lifting strategies by combining trunk lean and leg flexion, aiding in understanding injury risks and evaluating lifting behaviors in real-world settings.

Contribution

A novel, easy-to-calculate index that assesses whole-body lifting strategies using motion capture or video, with normative values established from healthy individuals.

Findings

Index effectively differentiates squat and stoop lifting phases.

Normative values range from below 30 for squatting to above 90 for stooping.

Index can be derived from video recordings for large-scale assessments.

Abstract

The widely held belief that squat lifting should be preferred over stoop lifting to prevent back injury is increasingly being challenged by recent biomechanical evidence. However, most of these studies only focus on very localized parameters such as lumbar spine flexion, while evaluations of whole-body lifting strategies are largely lacking. For this reason, a novel index, the Stoop-Squat-Index, was developed, which describes the proportion between trunk forward lean and lower extremity joint flexion, with possible values ranging from 0 (full squat lifting) to 100 (full stoop lifting). To enable the interpretation of the index in a real-life setting, normative values were established using motion capture data from 30 healthy pain-free individuals that were collected in the context of a previous study. The results showed mean index values of lower than 30 and higher than 90 for the most relevant phases of the squat and stoop movements, respectively, with mean index values differing significantly from each other for the full duration of the lifting phases. The main advantages of the index are that it is simple to calculate and can not only be derived from motion capture data but also from conventional video recordings, which enables large-scale in-field measurements with relatively low expenditure. When used in combination with lumbar spine flexion measurements, the index can contribute important information, which is necessary for comprehensively evaluating whole-body lifting strategies and to shed more light on the debate over the connection between lifting posture and back complaints.