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J M Stager

Publications and source records attributed to J M Stager.

29 records · Page 2Linked to original sources
PubMed1988

Phosphate supplementation, cardiovascular function, and exercise performance in humans.

The use of oral phosphate (Pi) supplements to improve muscular work performance has long been proposed without substantiating data. In a double-blind, crossover experiment 11 male runners ingested calcium Pi (176 mmol/day) or placebo for 4 days. On the 3rd treatment day, subjects ran an incremental maximal aerobic capacity test (VO2 max) on a treadmill, and on the 4th day a treadmill run to exhaustion at approximately 70% VO2max. By the 4th day of Pi loading, plasma Pi was significantly higher than control (P less than 0.05); however, erythrocyte Pi, 2,3-diphosphoglycerate, and O2 half-saturation pressure of hemoglobin (P50) were not elevated. VO2 max was not changed by the treatments (mean 62.9, 64.2, 64.9 ml.kg-1.min-1 for control, Pi, and placebo bouts, respectively) nor was submaximal run time to exhaustion (61.6 min for Pi, 65.5 min for placebo). Stroke volume at steady-state VO2 was decreased with Pi (P less than 0.05), whereas cardiac output tended (P = 0.07) to be lower. Greater arteriovenous O2 difference (P less than 0.05) with Pi suggested a peripheral effect that increased O2 extraction. We concluded that in healthy individuals Pi loading produced no improvement in work tolerance or aerobic capacity but did alter some aspects of cardiovascular function.

2,3-Diphosphoglycerate↗
PubMed1988

Menarche in athletes: the influence of genetics and prepubertal training.

It is unclear whether the later menarche observed in competitive athletes is due to genetic factors or environmental factors related to intense prepubertal training. In order to investigate the importance of these factors upon the age of menarche (AOM), 263 competitive swimmers and 71 women with no athletic experience were asked to complete questionnaires concerning general health and reproductive development. Based upon their responses, similar questionnaires were sent to the sisters of both groups. Complete data were obtained from 140 athlete/sister pairs and 43 control/sister pairs. Results indicate that the athletes were older at menarche than their sisters, the non-athletes, and the sisters of the non-athletes (14.3 yr, 13.7 yr, 12.9 yr, and 13.0 yr, respectively). The sisters of the athletes were significantly older at menarche than the controls and their sisters, while the AOM of the non-athletic controls and their sisters did not differ. The interpretation of the data is complicated by the fact that the sisters of the athletes were likely to be athletes (75%), while those of the control group tended to be non-athletic (74%). The athletes differed from their sisters who trained prior to menarche (13.9 years) and from those who did not engage in prepubertal training (13.1 years). Controls did not differ from any of their sister groups, nor did they differ from the untrained sisters of athletes. In terms of the similarity of the AOM within the sister pairs, the athletes/sisters and controls/sisters were equally similar. Significant correlations were observed between athletes and their sisters who trained prior to menarche and controls and their sisters who did not.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1987

Maximal respiratory pressures and pulmonary function in male runners.

To determine the effects of long term exercise on respiratory muscle strength, maximal inspiratory (Pl max) and expiratory (PE max) pressures, pulmonary volumes and capacities and anthropometric parameters were measured in a group of 101 male runners aged 16 to 58 years. The runners exhibited significantly (p less than 0.05) lower PE max (202 +/- 41 cm H2O and significantly greater residual lung volumes (RV) (2.08 +/- 0.49 L) than predicted values for normal subjects of similar height and age. Forced vital capacities were not different (p greater than 0.05) from values reported for normal non-smoking populations. These data suggest that running may cause a non-pathological increase in RV, perhaps mediated by reductions in expiratory muscle strength. Additionally, current RV regression equations developed for normal subjects may be inappropriate for use in running populations.

Adolescent↗
PubMed1987

The thyroid and hypoxic moderation of systemic hypertension in the spontaneously hypertensive rat.

Surgically thyroidectomized (TX), sham-operated euthyroid (EU), or thyroidectomized with dietary hormone replacement (RPL), 8-week-old male spontaneously hypertensive rats were subjected to 4 weeks of either of two altitude treatments: normoxia (N; lab altitude = 1520 m) or hypobaric hypoxia (H; simulated altitude = 3658 m). Systolic blood pressure (SBP) was attenuated in all hypoxic and in TX-N rats (p less than 0.05). Thyroidectomy reduced oxygen consumption, rectal temperature, and hormonal indices of thyroid function, as well as attenuating hypoxia-induced polycythemia and right ventricular hypertrophy. Thyroidectomy decreased the sensitivity of aortic rings to KCl and isoproterenol with no differences between EU-N and EU-H or between TX-N and TX-H apparent. Vessel responsiveness in RPL-H was consistent with the hypothyroid status indicated by hormonal measurement, while RPL-N vessel responsiveness was characteristic of euthyroid vessels. Since EU-H rats were euthyroid, with similar vascular responses to EU-N, hypoxia-induced attenuation of SBP does not require hypothyroid-like vascular alterations. Thus, hypoxia and thyroidectomy appear to mitigate systemic hypertension by different mechanisms.

Altitude↗
PubMed1984

Bone mineral content and menstrual regularity in female runners.

The relationship between bone mineral content and menstrual regularity in 10 amenorrheic runners (0-3 menses during the past year), 12 runners with regular menstrual cycles (10-12 menses during the past year), and 15 non-athletic women with regular menstrual cycles was investigated. Comparisons of the two groups of runners indicated no significant differences in body fatness, average weekly running distance, or average daily intake of calcium (Ca), phosphorus (P), and Ca/P ratios. Mean bone mineral content for the three groups, measured by photon absorptiometry, was 0.508, 0.529, and 0.544 g X cm-2, respectively, at 3 cm distal radius, and 0.707, 0.700, and 0.707 g X cm-2, respectively, at one-third distal radius, indicating no significant differences among the groups (P less than 0.05). However, a significant relationship (r = 0.77) was noted between bone mineral content and body fatness only in the amenorrheic runners. Within the amenorrheic population, the five thinnest runners had significantly lower mean bone mineral content values at 3 cm distal radius (0.457 g X cm-2) than the five runners with higher relative body fatness (0.559 g X cm-2). We conclude, therefore, that amenorrhea, independent of body composition, was not related to reduced bone mineral content in female runners. However, the combination of excessive thinness and amenorrhea may, in fact, predispose female athletes to reduced bone mass.

Adipose Tissue↗
PubMed1984

Delayed menarche in swimmers in relation to age at onset of training and athletic performance.

Competitive swimmers have been considered to be different from other female athletes in that their mean age at menarche is similar to that of nonathletes. However, it was hypothesized that if the delayed menarche observed in athletes of other sports is caused by prepubertal training, then swimmers should also exhibit delayed menarche as the majority of swimmers begin training prior to puberty. Furthermore, if early prepubertal training is the important factor in delaying menarche, then it was hypothesized that a relationship between performance and age at menarche in swimming is unlikely to exist. Thus, 345 competitive female swimmers and 549 control subjects completed questionnaires concerning general health, athletic training history, and age at menarche. Results indicated that, as a population, the mean age at menarche of the swimmers (13.4 yr) was significantly later than the controls (13.0 yr). When swimmers and controls were compared on an age-group basis, it was found that the difference in age at menarche was due to the data obtained from the older and more highly competitive swimmers. Assigning swimmers to different competitive levels or by performance in specific swimming events (50- or 100-yd freestyle; 45.7- or 91.4-m, respectively) indicated a significantly later age at menarche for the more competitive swimmers. Thus, there is evidence that the age at menarche and subsequent athletic performance in swimming are related; the later menarche observed in swimmers appears to be associated with factors that select for superior performance.

Adolescent↗
PubMed1983

Effect of triiodothyronine on body temperature at rest and during exercise in dogs.

To determine the effect of the thyroid hormones on body temperature at rest and during exercise, five mongrel dogs were trained to run on a treadmill and then treated with exogenous triiodothyronine (T3) (1 mg/kg) to elevate circulating T3 levels or propylthiouracil (PTU) (200 mg/day for 14 days) to lower endogenous T3 levels. When compared with levels in euthyroid controls at rest and during exercise, rectal temperature (Tre) was increased (P less than or equal to 0.01 and P less than or equal to 0.02, rest and exercise, respectively) in T3-treated dogs and decreased (P less than 0.05 and P less than 0.01) in the PTU-treated dogs. Although the rise in Tre from rest to exercise in the PTU trial was slightly less than that of the control runs (1.23 vs 1.44 degrees C, respectively; P = 0.05), it was similar to the rise in Tre observed in the T3 experiments (1.37 degrees C). Because T3 treatment resulted in an elevation in exercise oxygen consumption (VO2), untreated dogs were run at elevated work loads such that their VO2 matched that recorded when pretreated with T3. Exercise Tre in these experiments was lower (P less than 0.02) than after T3 treatment, even though the exercise metabolic rates were equivalent. It was concluded that 1) although T3 alters body temperature, the magnitude of the rise in Tre during exercise is not dependent on T3 concentration and 2) the effects of T3 on body temperature at rest and during exercise are mediated through mechanisms other than alterations in metabolic rate.

Animals↗
PubMed1981

Ventilatory endurance in athletes and non-athletes.

Do the ventilatory muscles (VM) of normal persons become fatigued while high ventilation is maintained during strenuous exercise? If so, then one effect of the intense training performed by endurance athletes should be an increase in VM endurance. To investigate this possibility, eight female endurance-athletes and eight female non-athletes were compared in studies of both short-term and long-term maximal ventilation. The two groups were matched for age, body size, and vital capacity. While athletes and non-athletes had similar short-term maximal ventilation (12-s MVV), the athletes displayed greater ventilatory endurance on two-long-term breathing tests. In the first, ventilation was increased 30 1/min every 4 min. Before exhaustion, athletes reached a ventilation that was a significantly greater fraction of their 12-s MVV (75% vs 67%, P less than 0.01), than did non-athletes. Although the energy cost (VO2) of submaximal levels of ventilation was identical in the two groups, athletes reached a significantly greater peak VO2 during this progressive test (P less than 0.05). In the second test of ventilatory endurance, 80% of the 12-s MVV was sustained until exhaustion. Endurance times averaged 11 min for athletes and 3 min for non-athletes (P less than 0.01). While these results do not rule out the possibility of genetic predisposition to high VM endurance in athletes, they are consistent with the possibility that VM training may occur in normal persons during forms of endurance exercise training.

Female↗
PubMedDate not supplied

Arterial O2 saturation and maximum O2 consumption in moderate-altitude runners exposed to sea level and 3,050 m.

Twelve trained runners, who were moderate-altitude (1,520 m) residents, were acutely exposed to sea level and 3,050-m altitude in a hypo-hyperbaric chamber. At 1,520 m, maximum O2 consumption (VO2 max) was 67.7 +/- 0.9 mL/kg/min, minute ventilation (V) at maximum exercise was 169.8 +/- 4.6 L/min, and arterial O2 saturation (SaO2) decreased from 93.3% +/- 0.9% at rest, to 84.5% +/- 1.6% at maximum exercise. Exposure to 3,050 m produced a lower VO2max (56.5 +/- 1.5, -16.5%), a similar V at maximum exercise (169.9 +/- 6.0), and a similar fall in SaO2 (from 89.1% +/- 0.8% to 79.5% +/- 0.8%). Exposure to sea level increased VO2max to 72.4 +/- 1.4 (+6.9%), reduced V at maximum exercise to 158.8 +/- 6.5, and induced a smaller fall in SaO2 (from 96.9% +/- 0.4% to 92.1% +/- 1.0%). These changes are comparable with those reported previously in athletes at sea level exposed to similar altitudes, suggesting that residence at 1,520 m does not improve VO2max in highly trained athletes acutely exposed to lower or higher altitudes.

Adolescent↗