In the present study of 213 healthy children, the relation between parental reports of activity level and laboratorydetermined physical fitness was examined. Results indicated that parental reports of activity level were associated with fitness for the entire sample. The association was most consistent among White children who resided in a household that was headed by their father.
We examined the effects of aerobic fitness and race on the diurnal rhythm of blood pressure of 175 healthy adolescents who performed a cycle ergometer maximal exercise test while oxygen consumption was measured. A median split of maximum oxygen consumption for boys and girls separately classified them as either "more-fit" or "less-fit" subjects. Ambulatory blood pressure recordings were also performed, and the data were analyzed for means while subjects were awake and asleep. Less-fit black boys had higher systolic pressures than more-fit black boys while awake (124 vs. 115 mm Hg;/><0.009) and asleep (117 vs. 108;p<0.001). Less-fit black boys also had higher systolic pressures than less-fit white boys while awake (114;/?< 0.002) and asleep (105; /?< 0.001), and they had higher systolic pressures than more-fit white boys while asleep (105;p<0.01). Less-fit black girls had higher systolic pressures than more-fit black girls while awake (116 vs. 109;p<0.004) and asleep (109 vs. 100;p<0.001). Less-fit black girls also had higher diastolic pressures than more-fit black girls while awake (71 vs. 66; p< 0.002) and asleep (66 vs. 61;p<0.001). In addition, less-fit black girls had higher systolic pressures than more-fit white girls while asleep (104; p< 0.05), higher diastolic pressures than more-fit white girls while awake (68;p<0.05) and asleep (60; p< 0.006), and higher diastolic pressures than less-fit white girls while asleep (61;/?< 0.001). These findings indicate that fitness influences ambulatory blood pressure profiles, particularly in black adolescents. {Hypertension 1990;15:810-814) P revious studies using ambulatory blood pressure monitoring have demonstrated racial differences in the diurnal rhythm of blood pressure in adolescents 1 and adults.2 -3 Specifically, black individuals and white individuals have similar levels of blood pressure while awake, but black individuals have higher levels of blood pressure while asleep. Aerobic fitness may be a second factor that influences the diurnal variation of blood pressure. Increased physical activity and aerobic fitness are associated with lower casual blood pressure, 4 -11 as well as a reduced risk for the development of hypertension and coronary heart disease.
12- 15 The purpose of the present study was to examine the effects of aerobic fitness and the interaction between aerobic fitness and race on the diurnal variation of blood pressure in healthy, normotensive adolescents.
Methods SubjectsA biracial sample of 226 healthy, normotensive children between the ages of 10 and 18 years was recruited as part of an ongoing study evaluating hypertensive risk factors in children. A total of 175 of the 226 children (77%) completed both the cycle ergometer maximal exercise test and the ambulatory blood pressure recording. Parental consent was obtained before testing.The sample included 80 boys and 95 girls, who were divided into "more-fit" and "less-fit" categories based on a median split of maximum oxygen consumption (Vc^max) performed separately for boys and girls. The...
The hypothesis that anterior hypothalamic (AH) sensitivity to norepinephrine (NE) is altered by chronic exercise in the heat was tested in male Sprague-Dawley rats. Treadmill exercise 6 days/wk for 3 wk at 21 m/min was performed at 23 degrees C (control; C) or at 35 degrees C (heat acclimated; HA), progressing from 20 to 50 min/day in 2 wk. Time for core temperature (Tco) to rise from 39.5 to 40.5 degrees C during a heat-tolerance test after conditioning increased (P less than 0.05) in the HA group. To test for a change in AH sensitivity, the change in Tco to 2-, 5-, 10-, 20-, and 40-micrograms doses of NE injected bilaterally into the AH was determined after conditioning. Dose-response regression lines showed that exercise in the heat increased the slope and shifted the Tco-NE dose relation to the left. In a separate series of experiments on 6 sedentary(s), 10 C, and 10 HA animals, the amounts of NE, dopamine, and 3,4-dihydroxyphenylglycol (DOPEG) were determined by high-pressure liquid chromatography in the AH, median preoptic area (PO), cortex, and cerebellum after 9 wk of conditioning. Results showed that in the PO there was a significant increase in NE and DOPEG in the HA vs. C group and a trend of increasing NE from the S to C to HA groups. The data indicate that exercise in the heat increases NE-induced peripheral heat-dissipating capacity and increases catecholamine storage in the PO.
Norepinephrine (NE) was injected bilaterally through implanted guide cannulas into the anterior hypothalamus (AH) of conscious male Sprague-Dawley rats (300-360 g) at rest and just before treadmill exercise (21.5 m/min for 30 min). Colonic (Tc), tail-skin (Ts), and ambient (Ta) temperatures were monitored each minute by use of a telethermometer. At rest (Ta = 23 degrees C), intrahypothalamic injections of 0.5-40.0 micrograms of NE, in a total of 1.0 microliter delivered within 30 s, produced a dose-dependent hypothermia with a 3-5 degrees C rise in Ts. NE (10 micrograms) injected 2 min before exercise (Ta = 23 degrees C) caused an immediate rise in Ts and a mean decline in Tc of 0.9 +/- 0.1 degree C (SE) below resting levels during exercise. This decline in Tc was statistically the same as that observed after the injections of 10 micrograms of NE at rest. Under control exercise conditions, Tc rose approximately 1 degree C and was associated with an initial decline (0.5 degrees C) followed by a rise (4.0 degrees C) in Ts. When the alpha-adrenergic receptor blocker phentolamine was injected 5-15 min before exercise, it caused a significant (P < 0.01) elevation in Tc during the ensuing exercise compared with controls. These results indicate that 1) over a dose range 0.5-40.0 micrograms, NE microinjected into the AH of the rt produces only hypothermia; 2) alpha-adrenergic receptors in the AH participate in the mediation of heat dissipation when the thermoregulatory system is challenged by the endogenous heat stress of exercise; and 3) exercise per se provides a nonthermal input to the temperature regulatory system that enhances heat dissipation.
Bilateral stainless steel guide tubes were stereotaxically implanted above the anterior hypothalamus (AH) of 12 male Sprague-Dawley rats (300-360 g). Beginning 3 days postsurgery, norepinephrine (NE) was injected into the AH each day at increasing depths below the guide tube until colonic temperature fell at least 0.8 degrees C. Subsequently, the effects of treadmill exercise at 21.5 m/min for 3 wk at 22 degrees C (n = 6) or 35 degrees C (n = 6) on the magnitude of the NE-induced hypothermia were investigated. Training duration ranged from 12 to 50 min/day, depending on the time required for colonic temperature of the heated rats to rise to a predetermined level: 40.4 degrees C on day 1, increasing 0.1 degree C/day to 41.5 degrees C on day 12 and thereafter. Before and after training, bilateral injections of NE (10 micrograms) at 22 degrees C at rest and just before exercise (21.5 m/min) caused the following mean +/- SE reductions in colonic temperature (degree C). (Formula: See Text). These reductions in colonic temperature were associated with sharp elevations in tail-skin temperature, but there were no significant differences in the response between the two groups. We conclude that repeated heat exposure increased the sensitivity of the AH to exogenous NE.
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