were significantly (P < 0.05) different from each other. We conclude that for moderate intensity knee extension exercise, conduit artery blood flow (Q FA ) kinetics may not be a reasonable approximation of blood flow kinetics in the microcirculation (Q cap ), the site of gas exchange. This temporal dissociation suggests that blood flow may be controlled differently at the conduit artery level than in the microcirculation.

The kinetic characteristics of muscle capillary blood flow (Q cap ) during recovery from exercise are controversial (e.g. one versus two phases). Furthermore, it is not clear how the overallQ cap kinetics are temporally associated with muscle oxygen uptake (V O 2 m ) kinetics. To address these issues, we examined the kinetics ofQ cap estimated from the rearrangement of the Fick equation

Gonzales JU, Thompson BC, Thistlethwaite JR, Harper AJ, Scheuermann BW. Forearm blood flow follows work rate during submaximal dynamic forearm exercise independent of sex. J Appl Physiol 103: 1950Physiol 103: -1957Physiol 103: , 2007. First published October 11, 2007; doi:10.1152/japplphysiol.00452.2007.-To test the hypothesis that sex influences forearm blood flow (FBF) during exercise, 15 women and 16 men of similar age [women 24.3 Ϯ 4.0 (SD) vs. men 24.9 Ϯ 4.5 yr] but different forearm muscle strength (women 290.7 Ϯ 44.4 vs. men 509.6 Ϯ 97.8 N; P Ͻ 0.05) performed dynamic handgrip exercise as the same absolute workload was increased in a ramp function (0.25 W/min). Task failure was defined as the inability to maintain contraction rate. Blood pressure and FBF were measured on separate arms during exercise by auscultation and Doppler ultrasound, respectively. Muscle strength was positively correlated with endurance time (r ϭ 0.72, P Ͻ 0.01) such that women had a shorter time to task failure than men (450.5 Ϯ 113.0 vs. 831.3 Ϯ 272.9 s; P Ͻ 0.05). However, the percentage of maximal handgrip strength achieved at task failure was similar between sexes (14% maximum voluntary contraction). FBF was similar between women and men throughout exercise and at task failure (women 13.6 Ϯ 5.3 vs. men 14.5 Ϯ 4.9 ml ⅐ min Ϫ1 ⅐ 100 ml Ϫ1 ). Mean arterial pressure was lower in women at rest and during exercise; thus calculated forearm vascular conductance (FVC) was higher in women during exercise but similar between sexes at task failure (women 0.13 Ϯ 0.05 vs. men 0.11 Ϯ 0.04 ml ⅐ min Ϫ1 ⅐ 100 ml Ϫ1 ⅐ mmHg Ϫ1 ). In conclusion, the similar FBF during exercise was achieved by a higher FVC in the presence of a lower MAP in women than men. Still, FBF remained coupled to work rate (and presumably metabolic demand) during exercise irrespective of sex. sex differences; forearm blood flow; handgrip; vascular conductance DURING TRANSIENT or sustained periods of increased muscle contractile activity, an increase in muscle perfusion must take place to deliver oxygen-rich blood to the active mitochondria as well as to remove metabolic by-products that may lead to muscle fatigue (11). The close coupling between muscle oxygen consumption and blood flow (3, 17) has been used as evidence to suggest that local muscle and/or vascular conditions exert considerable feedback regulation over vascular tone, in addition to the role that sympathetic outflow plays in maintaining mean arterial pressure (46). The matching of muscle perfusion to external work rate has been demonstrated in different muscle groups during isometric and dynamic exercise (1, 16). However, the influence of sex on the blood flow response to exercise has yet to be fully investigated, although sex differences in muscle blood flow have been hypothesized to be a factor contributing to the greater fatigue resistance observed in women compared with men (21).To date, the studies that have examined muscle blood flow during forearm exercise between women and men have relied primarily on ...

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We examined the validity and usefulness of a low-pass filter (LPFILTER) to reduce point-to-point variability and enhance parameter estimation of the kinetics of blood flow (BF). Computer simulations were used to determine the power spectrum of simulated responses. Moreover, we studied the leg BF response to a single transition in four subjects during supine knee-extension exercise using three methods of data processing [beat-by-beat, average of 3 cardiac cycles (AVG3 BEATS), and LPFILTER]. The power spectrum of BF containing the kinetics information (0.05; n=4). However, LPFILTER (cutoff=0.2 Hz) resulted in a significantly lower standard error of the estimate for all parameters (P<0.05). The means+/-SD for the standard error of the estimate for Beat-by-Beat, AVG3 BEATS, and LPFILTER were, respectively, time constant-phase 1=5.0+/-1.1 s, 4.5+/-2.1 s, and 0.3+/-0.2 s; time delay-phase 2=17.8+/-7.9 s, 12.8+/-7.5 s, and 1.4+/-1.4 s; time constant-phase 2=15.8+/-4.6 s, 9.9+/-2.9 s, and 1.1+/-0.5 s. In conclusion, LPFILTER appeared to be a valid procedure providing a high signal-to-noise ratio and data density and thus LPFILTER resulted in the smallest confidence interval for parameter estimates of BF kinetics.