with keying and data entry tasks. AU participants wer emle (although this was not a req uiremen t for part1c1pat10n), between the ages of 23 and 50 (median age 34). The n umber of years of experience working at a com puter terminal or word processor ranged from two to
18 years (median 10 years). Participants were not excluded based on previous episodes of work-related pain, but were required to be free from acute episodes of pain at the time of participation, and were therefore considered to be "normal" workers. Other exclusion cri teria included the presence of known neuromuscular musculoskeletal or other conditions that might negative ly impact the study results or the individual's well being. Upon obtaining informed consent, each participant's workstation was examined for major problems in terms of "ergonomic" setup, and such problems were corrected at least one month prior to participation. Ergobreak 1 version 2.2 was installed on each participant's computer at least two weeks prior to the data collection period. This computer program could be used to prompt users to take rest breaks at a given time interval, number of words keyed, or number of mouse-feet moved, as set by the user. For the purposes of this study, the program was set to prompt users to take breaks based on fixed time inter vals. The program was also capable of counting the number of words typed over a fixed interval of time. Participants were randomly assigned to one of three experimental groups according to their set time interval between microbreaks: a control group (where partici pants took breaks whenever they felt they needed to), a 20-min interval group, and a 40-min interval group. All microbreaks were of 30 s duration, based on the work of Henning et al. (1989).