Energy Availability And Reproductive Function In Female Endurance Athletes

Author : Karine Schaal
Publisher :
ISBN 13 : 9780355151145
Total Pages : pages
Book Rating : 4.1/5 (511 download)

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Download or read book Impact of Low Energy Availability on Ovarian Function, Training Adaptations, and the Acute Exercise Response in Female Runners written by Karine Schaal and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The practice of many endurance and aesthetic sports at a high level of competition imposes a very large energy expenditure on a daily basis. In certain sports, this energy demand can be so high that it becomes challenging for athletes to consume enough food to maintain adequate energy balance. In addition to this energetic challenge, many athletes partaking in these sports may strive to maintain a low body weight and minimize fat mass by restricting their energy intake, as a lean and light body type is thought to confer a performance advantage in weight-bearing endurance sports. Over time, the persistent mismatch between energy intake and expenditure leads such athletes into an energy-conserving, catabolic state. The direct endocrine and metabolic consequences of low energy availability are well documented, and include suppressed ovarian function, compromised bone health and immune function, and adverse changes in lipid profile and endothelial function. However, less attention has been paid to the impact that a hypometabolic state may have on the physiological response to exercise, training adaptations, and competitive performance outcomes in these women. Therefore, the studies presented in this dissertation aimed to 1), investigate the impact of both chronically low and acutely decreased energy availability on the neuroendocrine, cardiovascular and metabolic response to high intensity exercise in female runners, and 2), determine whether acutely decreased energy availability during a period of heavy training may increase the risk of developing a state of excessive fatigue, compromising training adaptations and performance outcomes. Chapter 1 presents a review of the existing literature on the endocrine-metabolic adaptations to low energy availability in exercising women, and discusses how low energy availability may also impair exercise performance and lead athletes to a state of excessive fatigue such as non-functional overreaching (NFOR) or overtraining syndrome (OTS). In Chapter 2, we compared the physiological response to exercise of female distance runners with hypothalamic amenorrhea (AM) with that of their eumenorrheic (EU), age and training-matched counterparts. We showed that AM runners’ catecholamine and lactate response to exercise was very strongly blunted compared to EU, together with a tendency for higher fatigue scores on the Profile of Mood States. These trends are similar to those previously reported in overtrained athletes, suggesting that the chronically hypometabolic state reflected by hypothalamic amenorrhea may predispose these athletes to excessive fatigue that may undermine high intensity exercise performance and training adaptations, despite their rigorous training regimen. In Chapter 3, we showed that in female runners reporting regular menstrual cycles, the ability to maintain their baseline energy availability through a 4 week period of intensified training (IT) was closely tied to the type of training adaptation obtained at the outcome of a 4-week phase of intensified training. Well adapted (WA) runners, who showed marked improvements in performance, successfully maintained their baseline EA during IT, as they reported an increase in perceived hunger and spontaneously increased their energy intake to match the increase in ExEE. By contrast, non-functionally overreached (NFOR) runners, who showed high perceived fatigue and prolonged impairment in running performance, showed no change in energy intake or hunger, resulting in a significant decrease in EA and plasma [leptin]. Furthermore, the magnitude of change in EA was strongly correlated to the change in running performance (R=0.61). Even though menstrual cycle length did not change, signs of ovarian suppression also appeared in NFOR, including decreased luteal phase length and reduced salivary [estradiol] at the mid-cycle peak and during the luteal phase. Finally NFOR runners did not show greater fat or weight loss than WA runners despite their energy-restricted state. Given the strong relationship between changes in EA during heavy training, and the type of training response obtained, this study highlights the importance, for NFOR-prone athletes, to increase their energy intake “by discipline”, as rather than to let their intake be solely be guided by changes in hunger. Finally, in Chapter 4, we described the changes in the physiological response to exercise of the same NFOR and WA runners. We showed that together with their impaired peak running performance, NFOR runners displayed blunted peak norepinephrine, epinephrine and lactate concentrations, heart rate, and systolic blood pressure responses at volitional exhaustion. They also showed a complete lack of any of the physiological adaptations to fixed submaximal running speeds that would be expected to occur as a result of IT, such as decreased sympathetic activation, heart rate or [lactate] at a given submaximal speeds - all desirable adaptations, that were observed in WA runners. By showing the drastic difference in training adaptations obtained between WA and NFOR runners, these findings highlight the importance of monitoring athletes closely during IT in attempt to avoid such excessive fatigue accumulation in susceptible individuals. Taken together, the studies presented here show that female runners maintaining either chronically low or acutely decreased energy availability are at increased risk of excessive fatigue accumulation that would severely undermine the fitness and performance gains intended from their rigorous training regimen. While the lack of menstrual periods in amenorrheic runners in Chapter 2 constitutes easily noticeable evidence of insufficient energy availability, the NFOR runners in Chapters 3 and 4 did not show any evident signs of energy conservation that would be easily noticed by the athletes themselves going about their daily lives; no increase in hunger, no significant weight loss, and seemingly regular, normal-length menstrual cycles. Therefore, NFOR-prone runners should be aware that a hypometabolic state may be the culprit for recurrent excessive fatigue, impairing performance and blunting training adaptations – while yielding no greater weight or fat loss than observed in their energy balanced, well adapted counterparts.