Repetitive shock and vibration are routinely encountered with the use of powered and non-powered hand tools, and have been associated with injuries to the proximal arm shoulder, and neck and with neurologic and neurovascular disorders of the hand. Standards for the control of disease from vibration, in particular ISO 5349, have been shown to be inapplicable to tools having a large impact component, e.g. hammers. This proposed research includes a laboratory and a field component. It evolves from a substantial tradition of laboratory based studies, and will explore the effects of tool impulse, temporal pattern, and high frequency as well as low frequency acceleration on acute physiological responses. These responses are transient threshold shifts (TTS) in the three major classes of mechanoreceptors of the fingertip - SAI, FAI, FAII- and changes in the surface electromyogram (SEMG). No prior TTS experiment has attempted to detect response thresholds in the SAI and FAI receptor, which are the two most important mechanoreceptor afferents for muscle activity. Understanding the cause of TTS deficits should provide useful insights for disease prevention through tool design and on the nature of shorter-term functional sensory deficits, which may be pertinent to hand-arm dysfunction and acute traumatic injury. Accordingly, construction workers, who use powered and non-powered impact hand tools and have high rates of hand injury are the target population of this study. Tools characteristics will be simulated in the laboratory; then laboratory results will be applied to actual tools in the field. Goals include address of unresolved scientific questions on risks from extrinsic forces associated with hand tools and the development of reliable and effective field assessment methods.