W. J. Duey

Cardiovascular and plasma catecholamine responses to exercise in blacks and whites.

The purpose of the present study was to assess possible racial differences in cardiovascular and plasma catecholamine responses to dynamic exercise. A biracial group of normotensive college-age men (15 blacks, 15 whites) were tested for maximal oxygen uptake, resting blood pressure, and heart rate. Subjects then rode a cycle ergometer at 25%, 50%, and 75% of peak oxygen uptake (6 minutes at each stage). Blood pressure and heart rate were measured during supine rest, seated rest, and at each stage of exercise with an automated blood pressure monitor. At each stage, venous blood was sampled to allow determination of plasma norepinephrine and epinephrine, and cardiac output was measured with the carbon dioxide rebreathing technique. The results indicated that resting blood pressure was similar for blacks and whites (114/68 versus 115/68 mm Hg, respectively). Blacks exhibited greater systolic and diastolic blood pressures during submaximal dynamic exercise. However, blacks also showed a trend toward a positive parental history of hypertension, which has been associated with an increased pressor response. Racial differences did not exist for heart rate or cardiac output, but blacks had higher values for total peripheral resistance both at rest and during exercise. Although no overall racial differences were seen for plasma catecholamine concentrations at rest, blacks had significantly lower levels of norepinephrine (1,275 versus 1,556 pg/ml) and higher levels of epinephrine (306 versus 216 pg/ml) than whites at the highest work rate. The current study confirms the increased pressor response to exercise in normotensive blacks. Blacks had an elevation in total peripheral resistance that was not accompanied by an increase in plasma norepinephrine levels.

Cardiovascular and metabolic costs of forward, backward, and lateral motion.

PURPOSE The purpose of this study was to compare the metabolic and cardiovascular responses of movement in forward (FM), backward (BM), and lateral (LM) directions. METHODS Thirteen athletes with the following characteristics (mean +/- SD) were evaluated: age 21+/-3 yr, height 172.0+/-9.0 cm, weight 62.92+/-9.05 kg, and VO2max 54.13+/-7.42 mL x kg(-1) x min(-1). Subjects were evaluated at 80.45 and 134.08 m x min(-1). A repeated measures ANOVA was used for statistical analysis (P < 0.05). RESULTS At 80.45 m x min(-1), the following respective VO2 mL x kg(-1) x min(-1) and heart rate (HR) beats x min(-1) responses were: FM = 12.42+/-2.29, 113+/-10; BM = 15.95+/-2.45, 132+/-16; and LM = 22.10+/-4.76, 140+/-15. Both VO2 and HR were significantly different between conditions: LM > BM > FM. At 134.08 m x min(-1), the following respective VO2 and HR responses were: FM = 27.15+/-2.51, 146+/-7; BM = 31.33+/-5.77, 168+/-11; and LM = 32.58+/-5.74, 169+/-10. At 134.08 m x min(-1) neither HR or VO2 were significantly different between LM or BM (LM, BM, > FM). Stride length and stride frequency were also significantly different between conditions. These results indicate the variation in the energy cost of FM, BM, and LM.

Skeletal muscle fibre type and capillary density in college-aged blacks and whites

The purpose of this study was to compare muscle fibre type proportions and capillary density in untrained, college-aged blacks (n = 14) and whites (n = 14). Both groups were similar in terms of peak oxygen uptake (VO2peak), measured during cycle ergometry (blacks: 42.6 +/- 4, whites: 44.3 +/- 4 ml.kg-1 min-1, mean +/- SD). Muscle samples were obtained from the quadriceps femoris (vastus lateralis) by the needle biopsy technique. Fibre type was determined by myosin ATPase stain (pH = 4.54) and capillaries were identified by amylase-periodic acid Schiff (PAS) stain. The percentage of type I, IIa, and IIb fibres in the blacks was 39.5 +/- 11.5, 40.0 +/- 8.4, and 22.8 +/- 9.8, respectively. In whites the percentage of type I, IIa, and IIb fibres was 44.9 +/- 8.5, 36.6 +/- 6.9, and 18.3 +/- 9.6, respectively. No significant differences were noted between the two racial groups for type I, IIa, or IIb fibres. Capillary density was 277 +/- 39/mm2 in the blacks compared to 289 +/- 32/mm2 in the whites. Capillary density was positively correlated to percentage of type I fibres (r = 0.497) and negatively correlated to percentage of type IIa fibres (r = -0.389), in the overall study population. These data suggest that if racial differences in fibre type do exist, such differences are small compared to the variability in this measure.

Metabolic responses to drafting during front crawl swimming

We examined the metabolic responses to front crawl swimming when following directly behind (drafting) another swimmer. Seven trained male swimmers participated as subjects. VO2max (l.min-1) was measured during a progressive tethered swim test and was also estimated from a 20 s sample of expired air collected immediately after an all-out, 549 m (600 yard) swim. On different days, each subject performed two 549 m trials at 95% of his maximal swim velocity, one with drafting and one without drafting, using a counter-balanced design. Underwater pace lights were used to establish the predetermined swim velocity. Drafting significantly reduced post-exercise VO2 (2.85 +/- 0.63 vs 3.12 +/- 0.66 l.min-1), blood lactate (3.4 +/- 0.6 vs 5.0 +/- 0.5 mM), and rating of perceived exertion (11.7 +/- 0.4 vs 14.9 +/- 0.5) (P less than 0.05). A repeated measures ANOVA (condition X distance) also revealed significant reductions in HR during the 549 m swim (137.7 vs 146.8 beats.min-1) (P less than 0.05). The results indicate that drafting results in a decrease in energy expenditure for the range of speeds examined.

Cardiovascular responses to exercise in sprinters and distance runners

The purpose of this study was to examine the cardiovascular responses of sprinters and distance runners to isometric (IE) and dynamic exercise (DE). Normotensive males were selected and grouped according to prior running performance: sprinter (N = 6) or distance runner (N = 6). Each subject completed an incremental DE (cycle ergometry) test (6-min stages) at 20%, 40%, and 60% of VO2peak, and 3 min of isometric handgrip at 30% of MVC. Blood pressure (BP), heart rate (HR), cardiac output (Q), oxygen uptake, and blood lactate were measured, while mean arterial blood pressure (MABP), cardiac index (CI), and systemic vascular resistance (SVR) were calculated during each stage of DE. BP and HR were measured during each minute of IE. Muscle biopsies of the vastus lateralis revealed a significant difference in capillary density (capillaries per mm2 and capillaries per fiber) between the sprinters and distance runners (323 +/- 23 vs 409 +/- 27 and 2.2 +/- 0.2 vs 3.2 +/- 0.3, P < 0.05) and for the percentage of Type I fibers (46.4 +/- 4% vs 64.8 +/- 7%, P < 0.05). The IE challenge elicited a greater BP response at minute 3 in the sprinters, which was associated with a greater HR response. During DE, there were no significant differences in BP or HR between the groups. However, at 60% of VO2peak, the distance runners had a significantly higher cardiac index and a lower systemic vascular resistance than the sprinters (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)