摘要:

The intent of this review was to examine the effects of hyperoxic gas mixtures on human performance. The evidence seems clear that performance is enhanced when O2-enriched gases are inhaled during exercise; however, the physiological mechanisms responsible for the improvement remain obscure. Increased pressure has a detrimental effect on performance, so that studies using hyperbaric oxygenation are ambiguous if the intent is to understand the effects of increased Po2. The large increases in maximal O2uptake with hyperoxia reported in the literature may be erroneous because of problems encountered with the Douglas bag technique when gases with elevated O2fractions are used. These apparent increases cannot be easily reconciled with published values for cardiac output and blood gas concentrations during exercise with hyperoxia. The effects of elevated Po2are apparently widespread and, to a degree, independent; these include effects on pulmonary ventilation, on vascular smooth muscle, and on cellular metabolism. The available data do not lend strong support to the hypothesis that improvement in O2delivery is responsible for the enhanced performance with hyperoxia. There are effects of hyperoxia on the pulmonary responses to exercise and on the acid-base responses. There is evidence that one or both of these mechanisms could play an important role in the changes in performance with hyperoxia.

ISSN:0195-9131    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

The incidence and etiology of altered menstrual cycle function in women engaged in endurance athletic activities were investigated by studying endocrine, anthropometric and training parameters in 41 cross-country runners. The prevalence of altered menstrual cycle patterns was significant higher in the subjects than in college-aged women; 49% reported normal cycles and 51% were either oligomenorrheic (46%) or amenorrheic (5%). No significant differences between those reporting normal menstrual cycling (N) and those reporting oligo/amenorrhea (O/A) were found in the following areas: number of miles run/week, number of years of training, age when training began, sum of skinfold thicknesses, somatotype, or post-exercise levels of growth hormone, prolactin, or hematocrit. However, a difference (P < 0.05) was found in the mean age of menarche (N = 12.9 ± 0.3 yr; O/A = 14.3 ± 0.5yr). In addition, more O/A (68%) than N (42%) began training in the year of or prior to menarche.Evaluation of seven runners from one school who qualified for the national meet (1 amenorrheic, 5 oligomenorrheic, and 1 normal) revealed that the basal estrogen, progesterone, prolactin, and thyroid hormone levels were normal and that there were normal luteinzing hormone and follicle-stimulating hormone responses to synthetic gonadotropin-releasing hormone (GuRH). These data are consistent with an alteration of hypothalamic-pituitary-ovarian function above the level of the pituitary.

ISSN:0195-9131    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

Six healthy adult females with presumptively normal menstrual cycles volunteered to exercise on a bicycle ergometer on five separate days (days 2, 8, 14, 20, and 26 of the menstrual cycle; day 1 = onset of menstruation). On each experimental day each subject exercised at four submaximal exercise intensities and at an exercise intensity that elicited a peak oxygen uptake. At rest and at each exercise intensity metabolic and thermoregulatory measurements were made. There were no changes at rest or at any exercise intensity relative to cycle day in absolute oxygen uptake (1·min−1). Similarly, mean peak oxygen uptake and average work time to exhaustion were not different during the various phases of the menstrual cycle. The mean core temperature (Tre) at each exercise intensity was elevated on days 14 and 20 above that observed during Dow (day 2) and the follicular phase (day 8). This implied a dissociation of metabolic responses from thermoregulatory responses to exercise during the human menstrual cycle similar to that previously observed in exercising febrile males.

ISSN:0195-9131    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

This study evaluated the effects of propranolol on ratings of perceived exertion (RPE), heart rate (HR), and systolic blood pressure (SBP) during graded exercise testing of myocardial revascularization surgery patients before hospital discharge. Eighty-six men performed a symptom-limited, graded exercise test on a treadmill an average of 11 d after surgery. Patients were assigned to three groups: those not taking propranolol (no-propranolol group, N = 54), those taking propranolol (propranolol group, N = 22), and those exhibiting exertional hypotension during testing (hypotensive group, N = 10). Test results showed that estimated METs during peak exercise were similar for the three groups. The propranolol group demonstrated a lower HR for submaximal and peak exercise when compared with the no-propranolol group, but RPE was the same for matched exercise intensities. The hypotensive group failed to increase SBP during exercise, but perceived the matched exercise intensities to he the same as the other two groups. The HR response of the hypotensive group was similar to that of the no-propranolol group. Thus, an abnormal SBP response during exercise was not reflected in a changed RPE when compared with patients who increased SBP appropriately. It was concluded that propranolol does not affect RPE during graded exercise testing soon after cardiac surgery.

ISSN:0195-9131    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

The purposes of the study were, 1) to assess the respective roles of locally released norepinephrine in the sinus node and of plasma catecholamines in the control of heart rate during exercise and 2) to verify whether the heart is a source of plasma catecholamines during exercise. Plasma catecholamines (radio-enzymatic assay) and heart rate were measured in the last minute of a 5-min exercise period (3.2 km·h−1, 39% slope) in six normal dogs, in six dogs treated with 5 mg·kg−1sotalol, and in six dogs sympathectomized with 50 mg·kg−16-hydroxydopamine. Compared to the exercise heart rate values of the normal dogs (228 ± 8 beats·min−1) and the sympathectomized dogs (226 ± 9 beats·min−1), the sotalol-treated dogs had significantly lower rates (148 ± 6 beats·min−1). However, plasma catecholamine response was higher in the sotalol-treated dogs (7380 ± 1350 pg·ml−1) and in the sympathectomized dogs (4280 ± 680 pg·ml−1) than in the normal dogs (1890 ± 360 pg·ml−1). Since the action of plasma catecholamines on the sinus node is potentiated by denervation hypersensitivity, it is suggested that in exercising normal dogs, heart rate control could be ensured by locally released norepinephrine rather than by plasma catecholamines. Plasma catecholamines were assessed in six normal dogs at rest and at various exercise levels (HR = 90–200 beats·min−1) and in blood sampled simultaneously in the aorta and the coronary sinus. Plasma catecholamines in the coronary sinus and aorta were similar at rest (490 ± 90 vs 580 ± 80 pg·ml−1, respectively) and at the low-intensity exercise (710 ± 140 vs 880 ± 120 pg·ml−1, respectively). For moderate and severe work loads, plasma catecholamine concentrations in the coronary sinus (960 ± 160 and 1570 ± 340 pg·ml−1, respectively) were lower than in the aorta (1380 ± 260 and 2950 ± 100 pg·ml−1, respectively). These results suggest that in exercising dogs the heart is not a source of plasma catecholamines.

ISSN:0195-9131    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

Studies on isolated muscle and resting man have demonstrated that altering CO2stores influences intracellular lactate production and/or tissue lactate release. In the present project, subjects (N = 6) performed steady-state exercise for 30 min while inspiring 0, 2, 4, or 6% CO2and 21% O2. They were tested on eight occasions, four at 50% and four at 65% &OV0312;o2max. Arterialized venous blood Pco2increased in proportion to F1CO2(P < 0.05). Blood pH had a similar but inverse relationship, decreasing from 7.371 to 7.233 (P < 0.05). The V1 increased directly with PCO2(P < 0.05), but no differences were found for &OV0312;o2or &OV0312;co2The R decreased in proportion to Pco2(P < 0.05) at both exercise intensities. Blood lactate was reduced (P < 0.05) with CO2. At 65% &OV0312;o2maxlactate had an inverse linear relationship with blood Pco2(P < 0.05). The mean lactate decreased 43% from 3.88 mM·1−1with 0% CO2to 2.22 mM·1−1with 6% CO2. The R shift suggests that carbohydrate metabolism may have been inhibited and lipid metabolism enhanced.

ISSN:0195-9131    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

The response of anaerobic threshold (AT) to endurance training and detraining was studied in 21 males (&OV0398; age = 25 yr). Members of the exercise group trained on a cycle ergometer at 80% of maximal oxygen uptake (&OV0312;o2max) for 30 min four times per week for 9 wk. Nine weeks of detraining followed. A step-wise incremented cycle ergometer test was used to measure maximal and submaximal values of metabolic variables at 3-wk intervals. The criterion for determination of the onset of metabolic acidosis was a systematic increase in the ventilatory equivalent for O2(&OV0312;E/&OV0312;o2) without an increase in the ventilatory equivalent for CO2(&OV0312;E/&OV0312;co2). Significant increases and decreases of &OV0312;o2maxfor the exercise group during training and detraining, respectively, were revealed by ANOVA. Following 9 wk of training, elevations of 70.4% and 19.4% had occurred in AT expressed as absolute &OV0312;o2(AT 1·min−1) and percent of &OV0312;o2max(AT-&OV0312;o2), respectively. The latter change was not statistically significant. Losses of training gains in AT (1·min−1) were significant after 6 and 9 wk of detraining. The results of this study indicate that 9 wk of training is of sufficient duration to cause a significant alteration in AT. Loss of this training gain occurs rapidly and appears to be similar to changes in &OV0312;o2max.

ISSN:0195-9131    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

The effect of work rate increase in ramp work tests was studied in six healthy subjects. Each subject exercised on a cycle ergometer with the work rate incremented by either 65.4 W·min−1and 49.0 W·min−1for the fast ramps or 8.2 W·min−1and 6.1 W·min−1for the slow ramps for male and female subjects, respectively. Gas exchange was monitored by open-circuit spirometry. Arterialized venous blood samples were obtained from a dorsal hand vein. The peak &OV0312;o2was not significantly different for fast (3218 ± 602 ml·min−1, &OV0398; ± SD) and slow (3237 ± 602 ml·min−1) ramp tests. Gas-exchange anaerobic threshold, determined by multi-segment linear regression of &OV0312;Evs &OV0312;o2, was similar for fast and slow ramp tests (1742 ± 415 and 1925 ± 639 ml O2·min−1, P > 0.05). The &OV0312;o2at which blood lactate increased 0.5 mM above resting levels was lower (1463 ± 259 ml·min−1, P < 0.05) than the gas-exchange anaerobic threshold for the slow ramp test. The &OV0312;o2at which blood lactate reached 2.0 mM was greater (2383 ± 247 ml·min−1, P < 0.05) than the gas-exchange anaerobic threshold for the fast ramp test. In addition to these lactate differences, blood pH and HCO−3did not change in direct proportion to the lactate concentration in either test. Blood Pco2was significantly (P < 0.05) greater at the point of exhaustion in the fast ramp test (42.2 ± 2.3 mmHg) than in the slow ramp test (26.7 ± 2.1 mmHg). It is concluded that the gas-exchange anaerobic threshold can be clearly dissociated from the blood lactate threshold by altering the work rate forcing function. Other mechanisms, such as H+efflux and CO2storage capacity, are more likely explanations for the gas-exchange anaerobic threshold.

ISSN:0195-9131    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

The claims that athletic performance, like all human behavior, are governed by three invariant “biorhythms” were tested for all men's metric world records in track and field from 1913–1977 (N = 700). Outstanding performances are said to occur during positive cycle phases; and poor performances, errors of judgment, and accidents, during the negative phases and particularly at crossover points (critical days). “Biorhythm” amplitudes were calculated, and a chi-square (X2) analysis was used to compare the frequencies of records occurring in the positive, negative, and critical phases of each cycle with a random model. The phase-distribution of records within each individual cycle fit the random model (X2≤ 2.22, P > 0.30). The combined effects of the three cycles, determined from the mean “biorhythm” amplitude (X2= 1.30, P > 0.20) and the number of cycles in each phase (X2= 3.50, P > 0.30), also showed no significant departure from the expected frequencies. The number of records broken on single or multiple critical days was as expected from the number of critical days in each cycle (X2= 3.37, P > 0.15). These data reinforce our previous study on Australian records and the preponderance of acceptable published research into sports, accidents, and medical data in that they provide no evidence of the existence or effects of “biorhythms.”

ISSN:0195-9131    

出版商:OVID    

年代:1982

数据来源: OVID

摘要:

A biomechanical model of the ankle joint was developed and was used to predict the forces at the ankle during the stance phase of running. Measurements from five cadavers were averaged to obtain insertion points and directions of pull of equivalent tendons with respect to the assumed center of the ankle joint. A minimum joint force solution was obtained by assuming that only two equivalent muscle groups could exert force at one time. Three subjects ran at 4.47 m/s across a force platform that recorded the external forces and moments acting on the foot. Cinematography was used to measure the foot and leg positions during stance. Peak resultant joint forces ranging from 9.0 to 13.3 times body weight and peak Achilles tendon forces ranging from 5.3 to 10.0 times body weight were predicted. Small variations in some cases resulted in large differences in predicted forces. The highest tendon forces predicted exceeded those reported to cause damage to cadaver tendons in other studies.

ISSN:0195-9131    

出版商:OVID    

年代:1982

数据来源: OVID