Influence of hand forces and handle size on power absorption of the human hand–arm exposed to zh-axis vibration

The effect of handle size and hand forces, on the power absorbed by the hand–arm system, was investigated in a laboratory study using seven healthy male subjects exposed to two levels of broadband random vibration in the 8–1000 Hz frequency range along the zh-axis. The measurements were performed with three instrumented cylindrical handles of different diameter (30, 40 and 50 mm). The influence of hand forces applied by the subjects holding the vibrating handles was investigated under nine different grip/push force combinations. The posture adopted by the subjects consisted of the bent forearm with elbow angle of 90° and neutral wrist position, as described in the ISO 10819 standard. The pressure distribution at the hand–handle interface was also measured to quantify the static contact force corresponding to each combination of grip force, push force and handle size. The hand–handle coupling force, as defined in ISO/WD 15230, was further evaluated by summing the grip and push forces. The measured total absorbed power revealed relatively low inter-subject variability (generally less than 12%). Total absorbed power was found to be better correlated with coupling force than the contact force, while most of the absorbed power occurred in the low-frequency range, below 200 Hz. The magnitude of power absorbed within the hand and arm was observed to be strongly dependent upon the handle size; larger handles cause higher absorption of energy. The results also suggested that the power absorption is influenced by the grip as well as push force. The results attained from ANOVA confirmed the significance of all studied factors, i.e. vibration magnitude, handle diameter, and the grip and push forces on the power absorbed into the human hand and arm exposed to vibration.