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Objectives: The objectives of the present study were (1) to evaluate the pressor response to an isometric handgrip exercise in normotensive black and white males; (2) to measure plasma catecholamine levels pre- and post-exercise, as an index of sympathetic nervous system activity; and (3) to quantify the pressor response to bolus intravenous injections of phenylephrine (an alpha-specific agonist)., Methods: Cardiovascular and catecholamine responses to an isometric handgrip exercise (3 minutes at 30% MVC) were measured in 15 normotensive blacks and whites. In another phase of the study, pressor responses to bolus injections of phenylephrine were assessed to evaluate alpha-adrenergic sensitivity., Results: The blood pressure in the blacks increased from 119/69 to 160/120 mm HG during isometric exercise, while in the whites it increased from 118/67 to 153/110 mm HG. The blacks exhibited a greater diastolic blood pressure reactivity, as evidenced by a significant race x time interaction (p < 0.05). The heart rate responses were not significantly different between the two groups. The plasma levels of norepinephrine were similar at rest, but were 25% lower in the blacks than in the whites following isometric exercise (p < 0.01). Black subjects also demonstrated an increased pressor response to intravenous injections of phenylephrine at rest (p < 0.05)., Conclusions: The enhanced vascular sensitivity to norepinephrine may have contributed to the greater exercise pressor response in the blacks.

The purposes of this study were to evaluate (a) the effects of step rate and upper body support on the VO2 and HR responses to fixed work rates on the StairMaster 4000 (SM), (b) the accuracy of the SM settings, and (c) how HR compared with that measured during grade-walking on a treadmill. Six subjects worked at a slow step rate for 6 min and then a faster step rate for the last 6 min of a 12-min test at SM settings of 4, 7, and 10 METs. Gas exchange and HR measurements were made at minutes 4-6 and 10-12. Variations in step rate had no effect on HR (P = 0.45) or VO2 (P = 0.84). The effect of using the arms and hands for support was studied using 6 subjects who worked for 12 min at 4, 7, and 10 METs; the first 6 min without support, and the second 6 min with support. Support resulted in lower HR (P = 0.017) and VO2 (P = 0.002) values at 10 METs. The measured MET values were about 20% lower than those specified by machine settings: True MET values = 0.556 + 0.745 (SM setting). Finally, at the same VO2, systematically higher (7-11 b.min-1) HR values were observed for the SM relative to the treadmill.

The purpose of this study was to investigate the relationship between hypoxia and heart rate (HR), pulmonary ventilation, plasma epinephrine (E) and norepinephrine (NE) at rest and during exercise at 40% of maximal oxygen uptake. Six subjects were exposed to inspired gas mixtures containing 21%, 19%, 17%, 15%, and 13% O2. The duration of exposure to each mixture was 10 continuous min at rest, followed by 10 continuous min during exercise. The order of the inspired gas mixtures was randomized. During the exercise test, HR was elevated with exposure to 15% and 13% O2 (p less than 0.001). Pulmonary ventilation was higher at 13% O2 than at the higher O2 percents (p less than 0.001). There were no significant changes in plasma E or NE at rest or during exercise in response to the gas treatments. These results indicate that acute exposure to hypoxic gas mixtures at rest and during light work does not result in significant increases in sympathetic nervous system activity, as judged by the plasma E and NE response.

Twelve males (six moderate drinkers and six abstainers) were studied for the influence of varying dosages of alcohol on cardiorespiratory function and work performance. The subjects underwent three separate maximal exercise tests which consisted of progressive workloads on the bicycle ergometer. Prior to each work bout the subject consumed either a placebo (0.0 ml.kg-1), small (0.44 ml.kg-1), or a moderate (0.88 ml.kg-1) dose of a 95 per cent ethanol solution. Analysis of the results indicated that the ingestion of a small or moderate amount of alcohol had no significant effect on heart rate, blood pressure, ventilation, oxygen uptake or work performance.