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

Area of Science:

• Biomechanics
• Human Movement Science
• Exercise Physiology

Background:

• Electromyography (EMG) studies often investigate latissimus dorsi activity during trunk movements.
• Previous research indicates high latissimus dorsi activation during trunk tasks, suggesting its importance for stability and movement.
• Inconsistent normalization methods in EMG studies, using either shoulder or trunk tasks, pose a challenge for accurate interpretation.

Purpose of the Study:

• To compare commonly used shoulder and trunk normalization tasks.
• To determine if trunk tasks elicit maximal activity in the latissimus dorsi muscle.
• To assess the implications of normalization methods on understanding latissimus dorsi function.

Main Methods:

• Ten healthy participants performed maximal isometric trunk and shoulder tasks.
• Electromyography (EMG) signals were recorded from the latissimus dorsi using surface and indwelling electrodes.
• EMG data were processed to obtain linear envelopes, and maximum activity levels were compared across tasks.

Main Results:

• Shoulder extension tasks produced significantly higher latissimus dorsi activity levels (over 1.5 times) compared to all other tested shoulder and trunk tasks.
• This result was consistent for both surface and indwelling electrode recordings.
• Maximal isometric trunk tasks did not yield maximal latissimus dorsi activation.

Conclusions:

• Maximal isometric trunk tasks are insufficient for normalizing latissimus dorsi electromyography (EMG) data.
• Using trunk tasks for normalization may lead to an overestimation of the latissimus dorsi's contribution to trunk movements.
• Shoulder extension is a more effective task for eliciting maximal latissimus dorsi activity for EMG normalization.