Vibrations transmitted from human hands to upper arm, shoulder, back, neck, and head

Area of Science:

• Biomechanics
• Occupational Health
• Human Factors Engineering

Background:

• Powered hand tools can generate significant low-frequency vibrations (<25 Hz).
• The transmission of this vibration to upper body structures (arm, shoulder, neck, head) and its adverse effects are not well understood.
• Musculoskeletal disorders (MSDs) of the shoulder and neck are prevalent among workers using heavy-duty tools, with vibration exposure being a contributing factor.

Purpose of the Study:

• To investigate the transmission of vibration from human hands to the upper arm, shoulder, neck, and head.
• To understand the biodynamic response and apparent mass of the hand-arm system.
• To provide data for developing effective intervention methods for MSDs.

Main Methods:

• Eight human subjects participated in a 1-D vibration test system experiment.
• Both left and right hand-arm systems were simultaneously exposed to vibration to simulate a working posture.
• Vibration transmission was measured using a laser vibrometer and accelerometers; apparent mass was also measured at the palm.

Main Results:

• Resonance frequencies were identified: upper arm (7-12 Hz), shoulder (7-9 Hz), and back/neck (6-7 Hz).
• Vibration transmission and biodynamic responses were influenced by hand-arm posture, applied hand force, and vibration magnitude.
• Transmissibility in the upper arm showed a trend similar to the apparent mass at the palm within major resonant frequency ranges.

Conclusions:

• Vibration from powered hand tools can transmit to the upper arm, shoulder, neck, and head.
• Understanding these transmission pathways and resonance frequencies is vital for mitigating MSD risks.
• The study provides valuable insights for designing safer tools and work practices to prevent occupational MSDs.