Sex differences in experimental measures of pain sensitivity and endogenous pain inhibition

Figures & data

Table 1 Participant characteristics

Characteristic	Overall, n=48	Men, n=24	Women, n=24
Age (years), mean (SD)	22.81 (4.60)	24.54 (5.03)	21.08 (3.41)
BMI, mean (SD)	26.33 (5.70)	26.33 (4.88)	26.33 (6.53)
Resting BP (mmHg), mean (SD)
Systolic	123.63 (12.74)	130.44 (10.35)	116.81 (11.29)
Diastolic	75.10 (9.79)	76.40 (11.57)	73.81 (11.29)
Ethnic background, n (%)
Caucasian	26 (54.2)	17 (70.8)	9 (37.5)
African American	16 (33.3)	5 (20.8)	11 (45.8)
Asian/Pacific	4 (8.3)	1 (4.2)	3 (12.5)
Islander
Hispanic	2 (4.2)	1 (4.2)	1 (4.2)
Education, n (%)
College graduate	8 (16.7)	20 (83.3)	0 (0)
In college	40 (83.3)	4 (16.7)	24 (100)

Abbreviations: BMI, body mass index; BP, blood pressure; SD, standard deviation.

Table 2 Depressive symptoms and sleep quality

Variables	Overall, mean (SD)	Men, mean (SD)	Women, mean (SD)
CES-D	10.10 (6.68)	7.88 (5.91)	12.33 (6.77)
PSQI	4.90 (2.14)	4.13 (1.42)	5.67 (2.46)

Abbreviations: CES-D, Center for Epidemiologic Studies Depression Scale; PSQI, Pittsburgh Sleep Quality Index; SD, standard deviation.

Table 3 Pearson correlations

Variable	1	2	3	4	5	6
1. Sex
2. CES-D	0.34*	–
3. PSQI	0.37*	0.47**	–
4. IPT tolerance	−0.43**	−0.11	−0.05	–
5. IPT pain intensity	0.21	0.16	0.13	−0.12	–
6. IPT pain unpleasantness	0.17	0.14	0.09	−0.18	0.81**	–
7. CPM	−0.30*	−0.19	−0.27	−0.04	−0.30*	−0.24

Note:

* P<0.05;

** P<0.01; sex coded as 1= men, 2= women.

Abbreviations: CES-D, Center for Epidemiologic Studies Depression Scale; CPM, conditioned pain modulation; IPT, ischemic pain task; PSQI, Pittsburgh Sleep Quality Index.

Figure 1 Differences in pain sensitivity between men and women in response to the IPT.

Notes: (A) IPT tolerance time; (B) ratings of pain intensity and pain unpleasantness.
Abbreviation: IPT, ischemic pain task.

Table 4 Pain sensitivity responses to the IPT and baseline and conditioned PPTs during concurrent cold water immersion to determine the magnitude of CPM at the forearm

Variables	Overall, mean (SD)	Men, mean (SD)	Women, mean (SD)
IPT
Tolerance (seconds)	446.65 (225.68)	543.54 (242.38)	349.75 (160.43)
Pain intensity	48.97 (20.88)	44.60 (19.57)	53.34 (21.63)
Pain unpleasantness	54.75 (20.35)	51.29 (18.65)	58.21 (21.75)
CPM
Baseline PPTs	357.25 (155.36)	411.15 (159.93)	303.35 (132.98)
Conditioned	416.79 (188.49)	506.71 (193.78)	326.86 (134.81)
PPTs
CPM (% change)	18.72 (29.03)	27.46 (33.78)	9.98 (20.55)

Note: All PPT values are presented as kilopascals (kPa).

Abbreviations: CPM, conditioned pain modulation; IPT, ischemic pain task; PPT, pressure pain threshold; SD, standard deviation.

Figure 2 Differences in endogenous pain inhibition between men and women.

Notes: (A) Baseline PPTs and conditioned PPTs; (B) CPM at the forearm.
Abbreviations: CPM, conditioned pain modulation; PPT, pressure pain threshold.