The effect of limited overfeeding during growth on muscle characteristics: a pig model.

Energy restriction affects the hypothalamus, leading to a decrease in production of reproductive and thyroid hormones. A decrease in reproductive hormones affects fertility and a decrease in thyroid hormones affects muscle metabolism. A pig model has been used to determine that reproductive function is negatively affected if the normal practice of overfeeding is limited during the late luteal phase of the estrous cycle. We used a sub-set of pigs from this study to examine effects of limiting overfeeding on thyroid hormones and skeletal muscle (i.e. maximal enzyme activities, and muscle fibre characteristics). Eighteen rapidly growing gilts were randomized into three groups: 1) feeding a high plane of nutrition throughout the first 15 days of the estrous cycle; 2) limited overfeeding (25% below the first group) for first 7 days of the estrous cycle (early luteal phase), followed by a high plane of nutrition for days 8-15 (late luteal phase); and 3) high plane of nutrition throughout the first 7 days of the estrous cycle, followed by 8 days of limited overfeeding. Muscle biopsies were collected from the triceps brachii, and blood samples were collected for assessment of thyroid hormones at days 0 (baseline), 8 and 16. There was no effect of limited overfeeding on thyroid hormones, maximal enzyme activities, muscle fibre area or muscle fibre type. Limited overfeeding in rapidly growing pigs does not affect thyroid hormone status or muscle characteristics.

Menstrual dysfunction in athletes: an energetic challenge.

Intense training programs that are insufficiently fueled by energy intake may lead to fatigue, impaired performance, and a broad spectrum of menstrual cycle disturbances. The effects of acute reduced energy availability and chronic energy deficiency on reproductive function, specifically luteinizing hormone secretion, will be examined, as well as possible recovery strategies.

Thyroid hormone concentrations and muscle metabolism in amenorrheic and eumenorrheic athletes.

The relationship between resting thyroid hormone concentrations and exercise muscle metabolism was examined among eumenorrheic endurance-trained (n = 11), amenorrheic endurance-trained (n = 8), and eumenorrheic nonathletic (n = 13) subjects. Muscle metabolism was assessed with 31Phosphorous magnetic resonance spectroscopy by measuring changes in phosphocreatine (PCr), inorganic phosphate (Pi), and pH during plantar flexion exercise and recovery. All groups had similar Pi/PCr ratios and pH changes during exercise. Eumenorrheic endurance-trained subjects had faster recovery rates for PCr and Pi/PCr following exercise compared to the nonathletes (p < .05) and faster recovery rates for PCr compared to amenorrheic subjects (p < .05). Thyroxine (T4) and triiodothyronine (T3) levels were significantly lower in amenorrheic subjects compared to both eumenorrheic groups (p < .05). It was concluded that routine training enhances muscle metabolism, as measured by phosphate recovery kinetics. This enhancement was not evident in amenorrheic athletes with reduced T3 and T4 concentrations.

Plasma concentrations of beta-endorphin in trained eumenorrheic and amenorrheic women.

OBJECTIVE: To characterize the pattern of plasma beta-endorphin throughout the normal menstrual cycle and test the hypothesis that beta-endorphin concentrations are elevated in trained women with amenorrhea compared with trained and sedentary eumenorrheic women. DESIGN: Cohort analytic study. SETTING: Academic research environment. PARTICIPANTS: Healthy female volunteers: 10 eumenorrheic sedentary, 11 eumenorrheic trained, and 11 amenorrheic trained women. INTERVENTIONS: Blood samples were collected three times per week for either one complete menstrual cycle (eumenorrheic sedentary and trained subjects) or for a 4-week period (amenorrheic trained subjects). MAIN OUTCOME MEASURE: Plasma beta-endorphin concentrations. RESULTS: beta-Endorphin levels varied considerably across the sampling period and were not associated with menstrual status, gonadotropin, or gonadal steroid concentrations. Average beta-endorphin levels were not different between the follicular and luteal phases for menstruating subjects, but were greater in the eumenorrheic athletes. Compared with eumenorrheic sedentary subjects, plasma beta-endorphin levels were higher in the athletic groups, regardless of menstrual status. CONCLUSION: There were no cycle-related beta-endorphin changes. Eumenorrheic and amenorrheic athletes have higher beta-endorphin concentrations that may reflect adaptations to intense training and not exercise-associated amenorrhea.

Thyroid hormone concentrations and skeletal muscle metabolism during exercise in anorexic females.

Food restriction has been shown to result in an impairment of thyroid status, as the body attempts to conserve energy. In turn, hypothyroidism has been associated with impaired oxidative muscle metabolism, which could negatively affect one's ability to perform exercise. The purpose of this study was to examine the relationship between thyroid status and muscle metabolism during exercise in anorexic (n = 8) and control (n = 13) female subjects. Thyroid status was evaluated by measuring resting serum triiodothyronine (T3) and thyroxine (T4) concentrations, and muscle metabolism was evaluated by 31phosphorus magnetic resonance spectroscopy during plantar flexion exercise. Concentration of T3 and T4 in anorexics were significantly lower than in controls. The ratio of inorganic phosphate to phosphocreatine (Pi/PCr) was significantly higher in the anorexic compared with the control subjects at lower (p < 0.05), but not higher, relative exercise intensities. Rates of PCr recovery were not different between anorexics (tau = 50.2 +/- 15.8 s) and controls (tau = 42.6 +/- 16.7 s). In conclusion, despite lower circulating thyroid hormones in anorexic compared with control subjects, differences in oxidative metabolism between these groups were small.

Body dissatisfaction and drive for thinness in high performance field hockey athletes.

The prevalence of eating disordered tendencies and its relationship to body composition was examined in elite female field hockey players. Eating Disorder Inventory (EDI) and body composition (skinfold) data were collected from 111 (92.5%) athletes from 12 teams at the 1994 Indoor Canadian National Tournament. Athletes at risk for developing frank eating disorders were identified using cutoff scores of clinically diagnosed patients with eating disorders. 19/111 (17.1%) demonstrated increased body dissatisfaction (BD), and 4/111 (3.6%) an elevated drive for thinness, suggesting that concern for body shape and size is a greater issue in field hockey than preoccupation with weight. Compared to athletes not at risk, those with elevated BD scores were significantly heavier, fatter, and had higher BMIs. Although it appears that these athletes may have reason to be dissatisfied, they may be at increased risk for initiating and sustaining weight controlling behaviours associated with eating disorders. Special care must be taken in any intervention strategy.

The effect of amenorrhea on calcaneal bone density and total bone turnover in runners.

To examine in athletes the effect of long-term amenorrhea on the skeleton, measurements of calcaneal density and whole body retention of 99mTc-imidodiphosphate were made in 42 women who could be allocated to one of 3 groups defined by their level of physical activity and by menstrual status. There was no difference in bone density between eumenorrheic normoactive females and either eumenorrheic or amenorrheic athletes. However, calcaneal density was significantly greater for each group than for previously measured sedentary controls. Total body bone turnover was greater in both eumenorrheic and amenorrheic athletes than in eumenorrheic normoactive women. Sustained, intense physical activity does not significantly increase calcaneal bone density over and above the increase associated with normal levels of activity. This is despite a significant increase in the rate of total body bone mineral turnover.

Endorphins and exercise.

The endogenous opioids seem likely to be assigned a significant role in the integrated hormonal and metabolic response to exercise. This article reviews the present evidence on exercise and the endogenous opioids, and examines their involvement in a number of widely disparate physiological processes. In considering the role of individual opioid peptides, it is important to remember that many of the tools and techniques now used are still relatively crude. Most studies have demonstrated that serum concentrations of endogenous opioids, in particular beta-endorphin and beta-lipotrophin, increase in response to both acute exercise and training programmes. Elevated serum beta-endorphin concentrations induced by exercise have been linked to several psychological and physiological changes, including mood state changes and 'exercise-induced euphoria', altered pain perception, menstrual disturbances in female athletes, and the stress responses of numerous hormones (growth hormone, ACTH, prolactin, catecholamines and cortisol). Many reports have described a role for the endorphin response as seen during exercise and have used the opioid receptor antagonist, naloxone, to investigate and verify the degree of involvement of the opioids. However, whether the observed increases in peripheral endorphin concentrations are sufficient to cause immediate mood changes, create menstrual cycle dysfunction or alter pain perception is still not resolved. A relatively new implication for the endorphins and associated changes with exercise is in ventilatory regulation. A number of studies have suggested that endogenous opioids depress ventilation and may, therefore, play a role in ventilatory regulation by carbon dioxide, hypoxia and exercise. It may also be possible that during exercise, the perception of fatigue is modulated by an increase of endogenous opioids.