Blunting of sympathetic vasoconstriction in exercising muscle is well-established. Whether it persists during the early post-exercise period is unknown. This study tested the hypothesis that it persists in human skeletal muscle during the first 10 min of recovery from exercise. Eight healthy young males (21.4 ± 0.8 yrs, SE) performed 7 min of forearm rhythmic isometric handgrip exercise at 15% below forearm critical force (fCF). In separate trials, a cold pressor test (CPT) of 2 min duration was used to evoke forearm sympathetic vasoconstriction in each of Rest (R), Steady State Exercise (Ex), 2–4 min Post-Exercise (PEearly), and 8–10 min Post-Exercise (PElate). A 7 min control exercise trial with no CPT was also performed. Exercising forearm brachial artery blood flow, arterial blood pressure, cardiac output (CO), heart rate (HR), forearm deep venous catecholamine concentration, and arterialized venous catecholamine concentration were obtained immediately prior to and following the CPT in each trial. CPT resulted in a significant increase in forearm venous plasma norepinephrine concentration in all trials (P = 0.007), but no change in arterialized plasma norepinephrine (P = 0.32). CPT did not change forearm venous plasma epinephrine (P = 0.596) or arterialized plasma epinephrine concentration (P = 0.15). As assessed by the %reduction in forearm vascular conductance (FVC) the CPT evoked a robust vasoconstriction at rest that was severely blunted in exercise (R = −39.9 ± 4.6% vs. Ex = 5.5 ± 7.4%, P < 0.001). This blunting of vasoconstriction persisted at PEearly (-12.3 ± 10.1%, P = 0.02) and PElate (-18.1 ± 8.2%, P = 0.03) post-exercise. In conclusion, functional sympatholysis remains evident in human skeletal muscle as much as 10 min after the end of a bout of forearm exercise. Persistence of functional sympatholysis may have important implications for blood pressure regulation in the face of a challenge to blood pressure following exercise.
Within individuals, critical power appears sensitive to manipulations in O2 delivery. We asked whether interindividual differences in forearm O2 delivery might account for a majority of the interindividual differences in forearm critical force impulse (critical impulse), the force analog of critical power. Ten healthy men (24.6 ± 7.10 years) completed a maximal effort rhythmic handgrip exercise test (1 sec contraction‐2 sec relaxation) for 10 min. The average of contraction impulses over the last 30 sec quantified critical impulse. Forearm brachial artery blood flow (FBF; echo and Doppler ultrasound) and mean arterial pressure (MAP; finger photoplethysmography) were measured continuously. O2 delivery (FBF arterial oxygen content (venous blood [hemoglobin] and oxygen saturation from pulse oximetry)) and forearm vascular conductance (FVC; FBF·MAP−1) were calculated. There was a wide range in O2 delivery (59.98–121.15 O2 mL·min−1) and critical impulse (381.5–584.8 N) across subjects. During maximal effort exercise, O2 delivery increased rapidly, plateauing well before the declining forearm impulse and explained most of the interindividual differences in critical impulse (r2 = 0.85, P < 0.01). Both vasodilation (r2 = 0.64, P < 0.001) and the exercise pressor response (r2 = 0.33, P < 0.001) independently contributed to interindividual differences in FBF. In conclusion, interindividual differences in forearm O2 delivery account for most of the interindividual variation in critical impulse. Furthermore, individual differences in pressor response play an important role in determining differences in O2 delivery in addition to vasodilation. The mechanistic origins of this vasodilatory and pressor response heterogeneity across individuals remain to be determined.
PURPOSETo identify if rapid vasodilatory responses differ between individuals with or without type 2 diabetes.METHODS13 males (7 type II diabetics (T2D), 6 healthy controls (CON)) lay supine with the arm at heart level and completed 6 trials of single handgripping contractions (3 trials/day/contraction intensity, on 2 separate days, 1 s contraction duration) at 10, 20, and 40 % of their maximal voluntary contraction (randomly ordered). Forearm brachial artery blood flow (FBF, echo and Doppler ultrasound), mean arterial pressure (MAP, finger photoplethysmography) were measured continuously.RESULTStension‐time integral of single contraction force production (kg·s) vs. FBF relationships were constructed for each individual. There was no difference in the slope (4.7 ± 2.9 vs. 4.8 ± 2.5) or y‐intercept (y‐int) (35.2 ± 32.5 vs. 23.3 ± 15.2) between T2D and CON. However, there was considerable variation in both the slope and y‐int between subjects in each group. T2D coefficient of variation (COV) of slope was 64% and y‐int was 93%. COV for the slope in CON was 52% and y‐int 65%. Despite the variation, the r2 value for each individual was strong, ranging from 0.34–0.7 (σ = 0.51 ± 0.14) in T2D and 0.44–0.97 (σ = 0.76 ± 0.22) in CON.CONCLUSIONOlder males exhibit substantial inter‐individual rapid vasodilatory responses to muscle contraction. These individual differences do not appear to be influenced by type 2 diabetes.
PURPOSETo determine if differences in O2 delivery (O2D) between healthy subjects predicts performance in a critical power (CP) test.METHODS10 healthy male subjects lay supine with the arm at heart level and completed 10 min of rhythmic maximal voluntary contractions (1 s contraction: 2 s relaxation duty cycle). CP was calculated as the average peak contraction force during the last 30 s of the trial where force plateaued. Forearm brachial artery blood flow (FBF) during exercise (echo and Doppler ultrasound) and O2D (FBF x arterial oxygen content ([haemoglobin] from venous blood sample and oxygen saturation from pulse oximetry)) were measured.RESULTSmeans ± SD. A wide range of O2D and CP was observed. O2D 101.5 ± 25.1 ml O2/min (range 70.92–154.1 ml O2/min) & CP 25.4 ± 6.0 kg (range 17.5–34.7 kg). O2D & FBF area under the curve (AUC, ml O2/forearm volume & ml/forearm volume) for the first 200 s of exercise were predictors of CP (r2 = 0.47, 0.48 p ≤ 0.03). However, O2D & FBF total AUC during exercise was the strongest predictors rather than steady state levels achieved (r2 = 0.63, 0.66 p ≤ 0.01).CONCLUSIONSConsiderable inter‐individual differences in oxygen delivery exist during an all out CP test. These differences account for much of the inter‐individual differences in CP, supporting the contention that vasodilatory responsiveness and capacity are important determinants of small muscle mass CP. NSERC
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