Shoulder joint load and muscular activity during lifting.

Area of Science:

• Biomechanics
• Occupational Health
• Human Movement Science

Background:

• Understanding shoulder joint and muscle loading is crucial for preventing injuries during manual handling tasks.
• Lifting moderate burdens from floor to table level is a common activity in various occupational settings.

Purpose of the Study:

• To investigate the load on the shoulder joint and muscles in healthy adults during different lifting techniques.
• To compare the biomechanical demands of four distinct methods for lifting a 12.8 kg object.

Main Methods:

• Surface electromyography (EMG) with linear envelope analysis was employed to measure muscle activation.
• A static biomechanical model was utilized to calculate shoulder loading moments of force.
• Participants performed four different lifting strategies with a 12.8 kg burden.

Main Results:

• The straight knee lift technique resulted in the lowest initial shoulder load.
• Peak shoulder load and muscle activation occurred in the late phase of all lifting methods.
• Allowing subjects to step forward before placing the burden down significantly reduced final load and activation.
• Anterior and lateral deltoid, and serratus anterior muscles showed the highest activation.
• The burden's weight accounted for approximately 80% of the shoulder load moment, requiring about 75% of maximum shoulder strength.

Conclusions:

• Lifting technique significantly influences shoulder joint and muscle loading.
• Optimizing lifting strategies, such as utilizing a straight knee posture and incorporating a step-and-lower motion, can mitigate shoulder stress.
• The high percentage of maximum shoulder strength required highlights the demanding nature of this lifting task.