Muscle response to pneumatic hand tool torque reaction forces

Area of Science:

• Occupational Biomechanics
• Human Factors Engineering
• Musculoskeletal Disorders

Background:

• Industrial tools like nutrunners generate significant torque reaction forces.
• These forces can impact operator biomechanics and muscle activity.
• Understanding these effects is crucial for preventing work-related musculoskeletal injuries.

Purpose of the Study:

• To investigate the impact of torque reaction force on forearm muscle activity and grip force.
• To analyze the influence of varying tool torque and reaction times.
• To determine if a reflex response is involved in muscle activation.

Main Methods:

• Surface electromyography (sEMG) measured forearm muscle activity in five subjects.
• Subjects operated four right-angle, air shut-off nutrunners with torques from 30 Nm to 100 Nm.
• Short (0.5s) and long (2s) torque reaction times were tested.

Main Results:

• Peak hand forces ranged from 89 N to 202 N, with horizontal force being dominant (>97%).
• Forearm flexor EMG activity during the torque-reaction phase was significantly higher than other phases.
• Increased tool torque and shorter reaction times led to greater flexor EMG activity and shorter EMG latencies.

Conclusions:

• Nutrunner torque reaction forces affect forearm extrinsic hand muscles via a potential reflex response.
• Operator grip force and muscle exertion are significantly influenced by tool parameters.
• Findings highlight the need for ergonomic considerations in tool design and usage to mitigate risks.