An evaluation of backpack harness systems in non-neutral torso postures

Area of Science:

• Biomechanics
• Ergonomics
• Occupational Health

Background:

• Traditional backpack research focuses on neutral postures, overlooking workers in non-neutral positions.
• Existing harness designs offer some comfort improvements for general users.
• Occupational settings often require workers to wear back-mounted devices in flexed postures.

Purpose of the Study:

• To evaluate the biomechanical loading effects of non-neutral trunk postures on wearers of back-mounted loads.
• To compare the effectiveness of a basic harness versus an advanced design with lateral stiffness rods and a hip belt.
• To inform backpack system design recommendations for workers in flexed postures.

Main Methods:

• Fifteen participants supported an 18.2 kg load in static forward flexed postures (15°, 30°, 45°, 60°).
• Electromyography (EMG) measured trapezius, erector spinae, and rectus abdominis activation.
• Subjective comfort ratings were collected for both basic and advanced harness designs.

Main Results:

• The advanced harness significantly reduced trapezius and erector spinae muscle activity at 15° and 30° flexion.
• These benefits diminished at greater flexion angles (45°, 60°).
• Subjective comfort ratings aligned with EMG findings, favoring the advanced design in shoulder and low back areas.

Conclusions:

• Advanced harness designs offer significant biomechanical and comfort improvements for mild forward-flexed postures.
• Effectiveness of advanced designs is reduced in deeper forward-flexed positions.
• Future design criteria should consider the interaction between harness features and degree of trunk flexion.