Correction of misinterpretations and misrepresentations of the female athlete triad.
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Adolescent↗
Biomedical subjects
N I Williams
Publications and source records attributed to N I Williams.
Meal energy content is related to features of meal-related ghrelin profiles across a typical day of eating in non-obese premenopausal women.
UNLABELLED: Some features of the meal-related profile of ghrelin correspond to acute energy intake, suggesting a role in short-term energy homeostasis. Yet, no studies have examined this relationship across a typical day of eating when effects of time of day and or cumulative energy intake may also exist. AIM OF STUDY: To examine the relation between ghrelin and acute energy intake by quantifying changes in ghrelin over 24 hours in response to three typical meals and a snack occurring throughout the day. METHODS: Fourteen non-obese women consumed three meals and a snack at specific times; total ghrelin was measured repeatedly over 24 hours. RESULTS: Significant correlations existed between: 1) meal calories and the post-meal trough (r = - 0.36; p < 0.05), and 2) the sum of breakfast and lunch calories and subsequent dinner rise (r = - 0.45; p < 0.02) and 3) the sum of breakfast and lunch calories and dinner peak (r = - 0.54; p < 0.003). Thus, as energy intake increased across the day, pre-meal rises of subsequent meals were reduced. CONCLUSION: Meal-related profiles of ghrelin are not only associated with the energy content of specific meals, but also with the accumulated calories prior to a subsequent meal, suggesting a role in the modulation of acute energy homeostasis.
Adult↗
Acute effects of moderate intensity resistance exercise on bone cell activity.
Resistance exercise has positive effects on bone mass, but little is known about the mechanisms by which this occurs. The purpose of this study was to determine if a single bout of moderate intensity resistance exercise alters biochemical markers of bone cell activity. Indices of bone turnover were measured in nine healthy, untrained men (21.9 +/- 1.2 yrs old), before and following a single 45 minute session of resistance exercise, and during a control trial. A cross-over design was used so that all participants performed both trials in random order. Blood samples were collected immediately before, immediately after, and at 1, 8, 24, and 48 hours post exercise and analyzed for bone-specific alkaline phosphatase (BAP), type I collagen propeptide (PICP), and type I collagen N-telopeptide (sNTX). Urine from the second morning void was collected over four days (day before, day of, and two days following exercise) and analyzed for type I collagen N-telopeptide (uNTX). Exercise resulted in a significant increase (p < 0.05) in the ratio of biochemical markers of bone formation to bone resorption eight hours post exercise, largely due to a decrease in sNTX. Markers return to baseline within 24 hrs. These data suggest that moderate intensity resistance training acutely reduces bone resorption, leading to a favorable change in overall bone turnover, for at least 8 hours post exercise in untrained young men. Further work is needed to determine if long-term benefits to bone strength follow with persistent training.
Adult↗
Circulating ghrelin is sensitive to changes in body weight during a diet and exercise program in normal-weight young women.
Ghrelin is directly involved with short-term regulation of energy balance. Although circulating levels of ghrelin are elevated in anorexia nervosa and reduced in obesity, the role of ghrelin in regulating long-term energy balance in healthy women has not been investigated. We examined the effects of a 3-month energy deficit-imposing diet and exercise intervention on circulating ghrelin in normal-weight, healthy women. Body composition, resting metabolic rate, and serum ghrelin were measured at pre-, mid-, and postintervention in controls (n = 7), who performed no exercise, and exercising women who remained weight stable (n = 5) or lost weight (n = 10). Exercise training occurred five times per week, and subjects were fed a specific diet. Ghrelin significantly increased over time (770 +/- 296 to 1322 +/- 664 pmol/liter) in the weight-loss group compared with the controls and the weight-stable group (P < 0.05). Changes in ghrelin were negatively correlated with changes in body weight (r = -0.61; P < 0.05). Body fat, body weight, and resting metabolic rate significantly decreased in the weight-loss group before the increase in ghrelin. These findings suggest that ghrelin responds in a compensatory manner to changes in energy homeostasis in healthy young women, and that ghrelin exhibits particular sensitivity to changes in body weight.
Adipose Tissue↗
The relationship of natural killer cell counts, perforin mRNA and CD2 expression to post-exercise natural killer cell activity in humans.
The aim of this study was to further investigate the mechanism of suppression of natural killer (NK) cell cytotoxic activity in peripheral blood following strenuous exercise. Blood was collected for analysis of NK cell concentration, cytotoxic activity, CD2 surface expression and perforin gene expression from runners (RUN, n=6) and resting controls (CONTROL, n=4) pre-exercise, 0, 1.5, 5, and 24 h following a 60-min treadmill run at 80% of VO2 peak. Natural killer cytotoxic activity, measured using a whole blood chromium release assay, fluctuated minimally in the CONTROL group and increased by 63% and decreased by 43% 0 and 1.5 h post-exercise, respectively, in the RUN group (group x time, P < 0.001). Lytic index (cytotoxic activity per cell) did not change. Perforin mRNA, measured using quantitative real-time polymerase chain reaction (QRT-PCR) decreased from pre- to post-exercise and remained decreased through 24 h. The decrease from pre- to 0 h post-exercise was seen predominately in the RUN group and was inversely correlated (r=- 0.95) to pre-exercise perforin mRNA. The NK cell surface expression of CD2 (lymphocyte function-associated antigen-2) was determined using fluorescent antibodies and flow cytometry. There was no change in the proportion of NK cells expressing CD2 or CD2 density. We conclude that (1) numerical redistribution accounted for most of the change in NK cytotoxic activity following a strenuous run, (2) decrease in perforin gene expression during the run was inversely related to pre-exercise levels but did not parallel changes in cytotoxic activity, and (3) CD2 surface expression was not affected by exercise.
Adolescent↗
Longitudinal changes in reproductive hormones and menstrual cyclicity in cynomolgus monkeys during strenuous exercise training: abrupt transition to exercise-induced amenorrhea.
Cross-sectional studies of exercise-induced reproductive dysfunction have documented a high proportion of menstrual cycle disturbances in women involved in strenuous exercise training. However, longitudinal studies have been needed to examine individual susceptibility to exercise-induced reproductive dysfunction and to elucidate the progression of changes in reproductive function that occur with strenuous exercise training. Using the female cynomolgus monkey (Macaca fascicularis), we documented changes in menstrual cyclicity and patterns of LH, FSH, estradiol, and progesterone secretion as the animals developed exercise-induced amenorrhea. As monkeys gradually increased running to 12.3 +/- 0.9 km/day, body weight did not change significantly although food intake remained constant. The time spent training until amenorrhea developed varied widely among animals (7-24 months; mean = 14.3 +/- 2.2 months) and was not correlated with initial body weight, training distance, or food intake. Consistent changes in function of the reproductive axis occurred abruptly, one to two menstrual cycles before the development of amenorrhea. These included significant declines in plasma reproductive hormone concentrations, an increase in follicular phase length, and a decrease in luteal phase progesterone secretion. These data document a high level of interindividual variability in the development of exercise-induced reproductive dysfunction, delineate the progression of changes in reproductive hormone secretion that occur with exercise training, and illustrate an abrupt transition from normal cyclicity to an amenorrheic state in exercising individuals, that is not necessarily associated with weight loss.
Amenorrhea↗
Evidence for a causal role of low energy availability in the induction of menstrual cycle disturbances during strenuous exercise training.
Cross-sectional and short-term prospective studies in humans support the concept that low energy availability, and not other factors associated with exercise, causes the development of exercise-induced reproductive dysfunction. To rigorously test this hypothesis, we performed a longitudinal study, examining the role of low energy availability on both the development and the reversal of exercise-induced amenorrhea, using a monkey model (Macaca fascicularis). Eight adult female monkeys developed amenorrhea (defined as absence of menses for at least 100 d, with low and unchanging concentrations of LH, FSH, E2, and P4) after gradually increasing their daily exercise to 12.3 +/- 0.9 km/d of running over a 7- to 24-month period. Food intake remained constant during exercise training. To test whether amenorrhea is caused by low energy availability, four of the eight amenorrheic monkeys were provided with supplemental calories (138-181% of calorie intake during amenorrhea) while they maintained their daily training. All four monkeys exhibited increased reproductive hormone levels and reestablished ovulatory cycles, with recovery times for circulating gonadotropin levels ranging from 12-57 d from the initiation of supplemental feeding. The rapidity of recovery within the reproductive axis in a given monkey was directly related to the amount of energy that was consumed during the period of supplemental feeding (r = -0.97; P < 0.05). Repeated measurements of plasma T3 concentrations, a marker of cellular energy availability, revealed a tight correlation between the changes in reproductive function and T3 levels, such that T3 significantly decreased (27%) with the induction and significantly increased (18%) with the reversal of amenorrhea (P < 0.05). These data provide strong evidence that low energy availability plays a causal role in the development of exercise-induced amenorrhea.
Amenorrhea↗
The role of exercise in the prevention and treatment of osteoporosis and osteoarthritis.
Osteoporosis and osteoarthritis are two distinctly different rheumatic conditions that target elderly, primarily female, populations. This article examines the scientific evidence supporting the use of exercise as a specific therapeutic modality, the general physiologic and psychological benefits of exercise, and the exercise programs currently recommended to combat these prevalent musculoskeletal disorders. Exercise is a valuable adjunct to treatment programs aimed at alleviating the risks and symptoms of osteoporosis and osteoarthritis. In addition to its potential impact on the disease processes themselves, exercise improves general health and well being, enhances quality of life, and preserves physical independence.
Biomechanical Phenomena↗
Effects of short-term strenuous endurance exercise upon corpus luteum function.
PURPOSE: The present study tested whether short-term, abruptly initiated training can cause corpus luteum dysfunction when exercise is limited to either the follicular or luteal phase of the cycle. METHODS: Reproductive hormone excretion and menstrual characteristics were studied in sedentary women who exercised only during the follicular (N = 5) or the luteal (N = 4) phase. Six women served as controls, three of whom exercised at a low volume and three who remained sedentary. Weekly progressive increments in exercise volume continued until either ovulation (follicular group) or menses (luteal group) occurred. Physical activity and nutrient intake were closely monitored with the intent to maintain body weight. RESULTS: No luteal phase disturbances occurred in any of the control subjects, whereas 40% of follicular and 50% of luteal exercisers experienced luteal defects. The proportion of menstrual cycles disrupted was not different between luteal and follicular exercisers (50% vs 30%, respectively) but was significantly greater than the proportion of cycles disrupted in control subjects (P < 0.05). CONCLUSIONS: These results suggest that exposure to abrupt onset of training can alter luteal function, regardless of the menstrual cycle phase in which exercise occurs. This study also demonstrates that a relatively low volume of exercise suffices to induce mild disturbances in luteal function.
Adult↗
Stimulation of luteinizing hormone secretion by food intake: evidence against a role for insulin.
In adult male rhesus monkeys, 1 day of fasting leads to a profound suppression of LH secretion that is rapidly reversed with refeeding. To test the hypothesis that changes in insulin secretion during fasting and refeeding mediate the changes in LH secretion, blood samples for LH measurement were obtained between 0900-2400 h from adult male rhesus monkeys (n = 9) on 1) a day when monkeys were refed their normal meal after a day of fasting, and 2) a day when monkeys were refed their normal meal, but endogenous insulin secretion was suppressed. Diazoxide (7.5-9.5 mg/kg.h) caused a 40-99% suppression of postmeal insulin secretion. However, no significant differences in LH pulse frequency, pulse amplitude, or mean serum LH levels were detected between control and diazoxide trials, even in animals in which insulin was markedly suppressed. Further, no correlation existed between the degree of insulin suppression and the magnitude of the meal-induced stimulation of LH. We conclude that meal-induced insulin secretion does not provide the stimulus mediating the meal-induced increase in LH secretion.
Animals↗
Strenuous exercise with caloric restriction: effect on luteinizing hormone secretion.
To test whether strenuous exercise with and without caloric restriction alters LH secretion, and whether these changes are apparent in the immediate post-exercise period, LH pulse parameters were studied in four moderately trained eumenorrheic women over three successive menstrual cycles. Blood samples were obtained 5 h before and 5 h after 90 min of running at 74% VO2max. Each test was preceded by a 7-d treatment of controlled diet and exercise (74% VO2max). During CONTROL, subjects were eucaloric on days 1-7, and performed no exercise on days 5-7. During STTI (short-term training increase), subjects were eucaloric and completed 90 min runs on days 5-7. During DIET/STTI, subjects consumed 60% of the calories necessary to maintain weight on days 1-7, and exercised as in STTI. A significant decrease in overall (0700-1830 h) LH pulse frequency during DIET/STTI compared with CONTROL and STTI treatments was observed. No changes were found in mean serum LH levels or peak amplitude. These results suggest that high-volume training combined with caloric restriction may predispose one to exercise-induced changes in LH pulse frequency, while adequate caloric intake may prevent these changes.
Adult↗
Effects of follicular phase exercise on luteinizing hormone pulse characteristics in sedentary eumenorrhoeic women.
OBJECTIVE: Current studies reveal little regarding the inception of exercise-induced LH changes during physical training. This study aimed to assess the susceptibility of the hypothalamic-pituitary axis to the acute physical stress of exercise in untrained, physically inactive women. The acute effects of submaximal endurance exercise upon the pulsatile LH secretion in the follicular phase were compared with those accompanying leisurely strolling for a similar time period. SUBJECTS: All subjects were eumenorrhoeic, as determined by biphasic temperature patterns, detection of the urinary LH surge, and mid-luteal serum progesterone levels. Subjects were not physically active and had little history of strenuous exercise (VO2max = 38.0 +/- 1.8) (mean +/- SEM) ml/kg/min). DESIGN: All women completed a 13.5-hour pulsatility test which included three consecutive 20-minute runs on a treadmill at 50, 60 and 70% of the subjects' maximum oxygen uptake (n = 16). Six of these same subjects completed a separate test on another occasion in which one hour of leisurely strolling was substituted for exercise. Blood was sampled every 10 minutes via an indwelling cannula for 4.5 hours before and 8 hours after one hour of exercise and or strolling. MEASUREMENTS: A pulse algorithm (Pulsar) was used to quantify LH pulse characteristics. RESULTS: Exercise produced no significant effects upon LH pulse frequency or mean serum LH concentration. However, exercise of moderate intensity caused a significant increase in LH pulse amplitude (P < 0.05). Strolling produced no significant changes in LH secretion. CONCLUSION: Acute exercise of moderate intensity in the follicular phase of untrained women is an insufficient stimulus to inhibit the GnRH pulse generator in the post-exercise period, yet may produce a slight stimulatory effect on the amount of LH released per pulse.
Adult↗
Non-weightbearing exercise may increase lumbar spine bone mineral density in healthy postmenopausal women.
Seven postmenopausal women exercised regularly at moderate intensities (60-80% of maximum heart rate) for eight months on bicycle ergometers. Evaluation of bone mineral density by dual photon absorptiometry revealed a significant (P < 0.01) + 3.55 +/- 1.43% (mean +/- SE) increase in lumbar spine density in the exercisers compared with the 2.44 +/- 0.81% decrease noted in seven sedentary controls. No significant difference in change in femoral neck density was noted between the two groups (+2.51 +/- 2.10% v -0.74 +/- 0.72% for exercisers and controls, respectively; P > 0.10). Dietary intake of calcium and vitamin D was similar in both groups, as was previous exposure to estrogen replacement therapy. These data provide evidence of a prospective nature that non-weightbearing exercise may be effective in reversing bone loss in healthy postmenopausal women.
Bicycling↗
Changes in body consciousness relate to regularity of exercise training.
Previous work has indicated improvement for scores on self-reported measures of body consciousness as aerobic fitness increased. To test whether exercise sufficient to improve aerobic fitness must be sustained on a regular basis to achieve positive changes in body consciousness, two separate periods of exercise training of 2 or 3 weeks duration were completed by nine female volunteers. The two exercise sessions were separated by 10 days of no exercise. Five women, as controls, did not exercise. Despite significant physiological improvement in the exercisers, no changes in self-perceived body self-consciousness were observed. Such changes may depend on the maintenance of a regular exercise regimen or the magnitude of physiological improvement.
Adult↗
Proteolipid protein: synthesis and assembly into quaking mouse myelin.
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Aging↗
The isolation and biochemical characterization of three subfractions of myelin from central nervous tissue of the adult rat.
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Animals↗