Sex differences in heat pain thresholds as a function of assessment methodand rate of rise

Studies of sex differences in the responses to experimentally induced pain demonstrate greater pain sensitivity among females than males. However, stu dies investigating heat pain responses have produced inconsistent results. Differences in stimulus characteristics and assessment methods probably acc ount for this variability. This study examined sex differences in the heat pain threshold as a function of two different assessment methods and varyin g rates of rise. Nineteen female and 18 male healthy volunteers underwent h eat pain threshold assessment via the method of levels and the method of li mits. In addition, both fast (4.0 degrees C/s) and slow (0.5 degrees C/s) r ates of rise were used for the method of levels assessments. In order to ex amine the reliability of threshold values, each subject participated in two sessions, separated by approximately 8 days. Females evinced lower thresho lds than males for the method of levels assessments with both slow and fast rates of rise tps < 0.05), while no sex differences emerged for the thresh old assessed via the method of limits. Test-retest reliability coefficients were relatively high. However, thresholds generally increased significantl y from session 1 to session 2. Between method correlations were generally l ow to moderate. These findings indicate that the method of levels may be mo re sensitive to sex differences than the more commonly used method of limit s. Also, thresholds appear to increase from session 1 to session 2, and thr esholds assessed via different methods are not strongly correlated. Potenti al implications of these results for experimental pain assessment are discu ssed.