Do maximal isometric trunk tasks produce maximum activity in latissimus dorsi?

Introduction: Electromyography (EMG) studies investigating latissimus dorsi activity during trunk tasks have reported high activation levels and described latissimus dorsi as an important contributor to trunk movement and stability. However, the normalisation of EMG data in these studies is inconsistent with some normalising to shoulder tasks and a majority normalising to trunk tasks. Therefore, this study aimed to compare commonly used shoulder and trunk normalisation tasks to determine if trunk tasks produce maximum activity in latissimus dorsi.

Methods: Ten asymptomatic participants completed maximal isometric trunk (extension, ipsilateral rotation and ipsilateral lateral flexion) and shoulder (extension and internal rotation) tasks while recording EMG signals from right latissimus dorsi using surface and indwelling electrodes. The signals were high-pass filtered, rectified then low-pass filtered to obtain an EMG linear envelope to represent muscle activity levels. The maximum activity levels across tasks were compared for each electrode type.

Results: Shoulder extension elicited significantly higher (>1.5 times) latissimus dorsi activity levels when recorded using both surface and indwelling electrodes compared to other shoulder and trunk tasks.

Conclusion: Maximal isometric trunk tasks do not produce maximal latissimus dorsi activity and therefore when used for normalisation purposes potentially overestimate the contribution of latissimus dorsi to trunk tasks.