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

Abstract

Some powered hand tools can generate significant vibration at frequencies below 25 Hz. It is not clear whether such vibration can be effectively transmitted to the upper arm, shoulder, neck, and head and cause adverse effects in these substructures. The objective of this study is to investigate the vibration transmission from the human hands to these substructures. Eight human subjects participated in the experiment, which was conducted on a 1-D vibration test system. Unlike many vibration transmission studies, both the right and left hand-arm systems were simultaneously exposed to the vibration to simulate a working posture in the experiment. A laser vibrometer and three accelerometers were used to measure the vibration transmitted to the substructures. The apparent mass at the palm of each hand was also measured to help in understanding the transmitted vibration and biodynamic response. This study found that the upper arm resonance frequency was 7-12 Hz, the shoulder resonance was 7-9 Hz, and the back and neck resonances were 6-7 Hz. The responses were affected by the hand-arm posture, applied hand force, and vibration magnitude. The transmissibility measured on the upper arm had a trend similar to that of the apparent mass measured at the palm in their major resonant frequency ranges. The implications of the results are discussed.

Relevance to industry: Musculoskeletal disorders (MSDs) of the shoulder and neck are important issues among many workers. Many of these workers use heavy-duty powered hand tools. The combined mechanical loads and vibration exposures are among the major factors contributing to the development of MSDs. The vibration characteristics of the body segments examined in this study can be used to help understand MSDs and to help develop more effective intervention methods.

Keywords: Hand-arm vibration; Hand-transmitted vibration; Head; Neck; Shoulder.

Fig. 1

Pictorial views of the instrumentation setup, a test subject with one of the two arm postures, and the adapters. (a) Retro-reflective tape was attached to the skin at 5 measurement locations for laser measurements. Transmissibility to the wrists and head were measured with three tri-axial accelerometer-equipped adapters. (b) The three adapters that were used during the experiments.

Fig. 2

Input vibration spectra.

Fig. 3

The averaged total vibration transmissibility of the 8 subjects at the forehead and both wrists measured with the 3 adapters.

Fig. 4

The averaged total vibration transmissibility of the 8 subjects at the neck (P1), back (P2 and P3), shoulder (P4), and upper arm (P5) measured with the 3-D laser vibrometer.

Fig. 5

Transmissibility to the forehead in all three vibration directions measured from one subject.

Fig. 6

3-D laser vibrometer measured total vibration transmissibility spectra of (a) one individual subject at all 5 measurement locations; (b) two subjects at the back of upper body (P2) with different arm postures.

Fig. 7

Effect of push force on the averaged vibration transmissibility.

Fig. 8

Effect of arm posture on the averaged vibration transmissibility.

Fig. 9

Effect of input vibration magnitude on the averaged vibration transmissibility.

Fig. 10

Correlations of the upper arm transmissibility and apparent mass at the palm from the spectra of individual subjects and the mean of eight subjects.

Fig. 11

The averaged total transmissibility measured at the wrist and upper arm from a previous study (Xu et al., 2015) and the current study.

Fig. 12

The averaged total transmissibility functions at six measurement locations and the apparent mass measured at the palm.