Maximum isometric trunk muscle strength and activity at trunk axial rotation during sitting

Area of Science:

• Occupational biomechanics
• Ergonomics
• Musculoskeletal research

Background:

• Tractor drivers often adopt twisted trunk postures during field work.
• Understanding the biomechanics of trunk axial rotation is vital for agricultural safety.

Purpose of the Study:

• To quantify trunk axial strength and muscle activity in relation to trunk twisting angles.
• To compare tractor drivers and office workers regarding trunk rotation biomechanics.
• To investigate the influence of twisting direction on trunk performance.

Main Methods:

• Nine tractor drivers and nine office workers performed isometric maximum efforts at various trunk prerotation angles (-40 to 40 degrees).
• Measurements included exerted torque, true prerotation angle, and muscle activity (obliquus externus, rectus abdominis, erector spinae).
• Trunk twisting was performed in both clockwise and counterclockwise directions.

Main Results:

• Maximal torques were higher when prerotation was opposite to the exertion direction (65-145 Nm).
• Significant differences in obliquus externus and erector spinae activity were observed based on twisting direction.
• Muscle activity of obliquus externus and rectus abdominis varied with the degree of prerotation angle.

Conclusions:

• Trunk axial rotation performance is direction-dependent, impacting maximal torque generation.
• Prerotation angle and direction significantly influence trunk muscle activation patterns.
• Further research is needed to explore the role of passive tissues and deeper muscles in trunk axial rotation.