Circulatory changes in the pelvic organs were found in a study of female tractor drivers; vascular tone decreased and venous stasis occurred at times, depending on the intensity and duration of the vibration (Engberg 1993). Excessive physical strain has been associated with injury events in women (Pickett et al. 1995). Ahonen et al. (1990) reported the physical strain of dairy farming to be high in women because of heavy work tasks and relatively low maximal oxygen uptake (VO2max).