Sex-speciﬁc inﬂuence of aging on exercising leg blood ﬂow

Proctor DN. Sex-speciﬁc inﬂuence of aging on exercising leg blood ﬂow. Appl Physiol 2008. work suggests that healthy human aging is associated with sex-speciﬁc differences in leg vascular responses during large muscle mass exercise (2-legged cycling) (Proctor DN, Parker BA. Microcirculation 13: 315–327, 2006). The present study determined whether age (cid:1) sex interactions in exercising leg hemodynamics persist during small muscle mass exercise that is not limited by cardiac output. Thirty-one young (20–30 yr; 15 men/16 women) and 31 older (60–79 yr; 13 men/18 women) healthy, normally active adults performed graded single-leg knee extensions to maximal exertion. Femoral artery blood velocity and diameter (Doppler ultrasound), heart rate (ECG), and beat-to-beat arterial blood pressure (mean arterial pressure, radial artery tonometry) were measured during each 3-min work rate (4.8 and 8 W/stage for women and men, respectively). The results (means (cid:2) SE) were as follows. Despite reduced resting leg blood ﬂow and vascular conductance, older men exhibited relatively preserved exercising leg hemodynamic responses. Older women, by contrast, exhibited attenuated hyperemic (young: 52 (cid:2) 3 ml (cid:1) min (cid:3) 1 (cid:1) W (cid:3) 1 ; vs. older: 40 (cid:2) 4 ml (cid:1) min (cid:3) 1 (cid:1) W (cid:3) 1 ; P (cid:4) 0.02) and vasodilatory responses (young: 0.56 (cid:2) 0.06 ml (cid:1) min (cid:3) 1 (cid:1) mmHg (cid:3) 1 (cid:1) W (cid:3) 1 vs. older: 0.37 (cid:2) 0.04 ml (cid:1) min (cid:3) 1 (cid:1) mmHg (cid:3) 1 W (cid:3) 1 ; P (cid:5) 0.01) to exercise compared with young women. Relative (percentage of maximal) work rate comparisons of all groups combined also revealed attenuated vasodilator responses in older women ( P (cid:5) 0.01 for age (cid:1) sex (cid:1) work rate interaction). These sex-speciﬁc age differences were not abolished by consideration of hemoglobin, quadriceps muscle, muscle recruitment, and mechanical inﬂuences on muscle perfusion. Collectively, these ﬁndings suggest that local factors contribute to the sex-speciﬁc effects of aging on exercising leg hemodynamics in healthy adults. model with work rate as the within-individual factor and age and sex as the between-individual factors and an autoregressive variance-covariance structure was used to determine differences between young and older subjects in outcome variables. A Bonferroni post hoc adjustment was performed when signiﬁcant age (cid:1) work rate differences were detected. Slopes of each individual’s linear regression line were determined mathematically (change in outcome variable/change in work rate), excluding rest and passive exercise and compared within sexes using a one-way ANOVA. To test for age (cid:1) sex interactions (i.e., whether the effect of age on leg hemodynamic responses to exercise differed by sex), relative responses to graded knee extensor exercise were examined with a random-coefﬁcients model (Proc Mixed), using a continuous predictor (work rate as a percentage of maximal work rate attained) and ﬁtting a random intercept and slope with work rate as the within-individual factor and age, sex, and age (cid:1) sex as the between-individual factors. An autoregressive variance-covariance structure was used to determine differences between subject groups in outcome variables (23).