Predictors of perceived effort in the shoulder during load transfer tasks

Area of Science:

• Biomechanics
• Neuroscience
• Human Factors

Background:

• Understanding muscular effort perception is crucial for ergonomics and injury prevention.
• Previous research often focused on direct measures of muscle activity or joint forces.

Purpose of the Study:

• To investigate the relationship between physical loading in the shoulder and the perception of muscular effort.
• To determine if biomechanical models or direct muscle activity measures better explain effort perception.
• To assess the impact of subject and task-specific variables on effort perception.

Main Methods:

• Utilized two shoulder biomechanical models and experimental muscle activity data (electromyography).
• Assessed physical exposure during reaching tasks.
• Quantitatively correlated effort perception with resultant torque, muscle force predictions (MFPs), and EMG data.

Main Results:

• Resultant torque (r² = 0.50) and MFPs (r² = 0.42) were better predictors of effort perception than EMG (r² = 0.26).
• Muscle data did not explain effort perception variability better than torque data alone.
• Including subject and task variables significantly improved model explanatory power (torque: r² = 0.74; MFP: r² = 0.67; EMG: r² = 0.64).

Conclusions:

• Shoulder effort perception is not solely determined by motor commands.
• Effort perception is a complex, integrative process influenced by factors such as posture and task objectives.
• Sensory feedback likely plays a significant role in modulating effort perception.