THYROID HORMONES, PERFORMANCE, AND PSYCHOLOGICAL CHANGES ON OVERTRAINING IN FEMALE DISTANCE RUNNERS

Statement of the Problem: Overtraining (OT) is common in endurance sports. Perturbations in the hormonal milieu are common throughout OT literature. Thyroid hormones (TH) are altered by energy imbalances, and these imbalances are often present in female endurance athletes. Thyroid hormones also regulate metabolism, energy production, and therefore they may play a role in commonly cited symptoms of OT in these athletes. Alterations in TH status often occur slowly, and research investigating TH and their relationship in overtrained athletes is sparse. PURPOSE: The purpose of this study was to investigate relationships in TH and commonly cited symptoms of OT in collegiate track and field (T&F) endurance runners. METHODS: Sixteen female track and field middle (MD; n=9; age: 20.21 ± 1.49 yrs; height: 167.86 ± 5.04 cm; body mass: 57.97 ± 5.05 kg; VO2MAX: 53.62 ± 6.04 ml/kg/min) and long (LD; n=7; age: 20.47 ± 1.53 yrs; height: 162.48 ± 6.11 cm; body mass: 56.15 ± 5.99 kg; VO2MAX: 61.94 ± 3.29 ml/kg/min) distance runners participated in a 14 week descriptive study. Thyroid stimulating hormone (TSH), triiodothyronine (T3), and thyroxine (T4), were collected at the beginning of the indoor T&F (PRE) and end of the outdoor T&F season (POST). Dietary intake and vertical jump power (VJP) were tested at PRE, MID, and POST season. A fatigue scale was administered weekly, and percent change (ΔRT) in race time (season best v.s. championship performance) was calculated. Wilcoxon-sign ranked tests were used to determine changes in hormonal, dietary, and performance measures over time. Spearman’s rho correlation coefficient was used to determine relationships between thyroid hormones, dietary intake, performance variables, and commonly cited symptoms of overtraining. Statistical significance was set at an alpha level of p ≤ 0.05. RESULTS: Fatigue was significantly lower at week 2 compared to MID season (p=0.016), week 12 (p=0.018) and POST (p=0.007). There was a significant correlation between fatigue at week 12 and running performance at the end of the season (ρ= -0.741, p= 0.004). Vertical jump power significantly increased PRE to MID season in MD and LD. Power significantly deceased MID to POST in MD. There were no significant changes in TSH, T3 and T4 from PRE to POST. There were significant correlations between total caloric intake at POST and peripheral hormones (T3 POST; ρ = 0.900, p= 0.037. T4 POST; ρ= 0.667, p= 0.050). The percent change (PΔ) in T3 from PRE to POST was significantly correlated with running performance at the end of the season (ρ=-0.700, p=0.036). Most of the subjects fell below current the RDA for carbohydrates and protein at PRE and POST. There was a significant relationship between caloric intake relative to lean body mass (kcal•kgLBM) at PRE and fatigue at week 1 (PRE) (ρ= 0.521, p=0.046). CONCLUSION: There were no significant differences between PRE and POST thyroid hormone concentration. Thyroid hormones are related to other variables of important in assessing the overall training state of the endurance athlete. Resting thyroid hormone concentrations may change too slowly to be a frequently used marker of monitoring overtraining status. Using weekly fatigue scales, monitoring dietary intake, and the utilization of VJP may be more readily available markers to assess overtraining and overall training status of collegiate female

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INTRODUCTION
To be successful in sport, athletes must balance energy intake and energy expenditure, however not all athletes achieve energy balance (34) and may be subject to overtraining. Works by Kreider et al. define overtraining (OT) as "an accumulation of training and/or non-training stress resulting in long-term decrement in performance capacity with or without related physiological and psychological signs and symptoms of maladaptation in which restoration of performance may take several weeks or months (26). In addition to negatively affecting performance, a chronic negative energy balance can affect reproductive and skeletal health. Thyroid hormones (TH) are involved in these systems, regulated by nutritional intake, and are key regulators in metabolism, growth, recovery, and mood. The relationship between thyroid hormones and overtraining however, has not been studied extensively.
Overtraining is common in endurance sports. The mechanisms responsible for OT are difficult to identify, however energy imbalance, hypothalamic imbalances, and autonomic neuromuscular fatigue are important factors (25). Iron deficiency may contribute to OT in some female athletes. In this case, athletes may be supplemented with more iron, however this additional supplementation may elude the deeper cause of this deficiency, which is most likely poor dietary intake and energy imbalance (37).
Many hormones such as TH, growth hormone (GH) and cortisol (C) are influenced by energy balance and therefore play a key role performance and recovery in the overtraining status of an athlete.
Appropriate macronutrient intake is essential to elicit positive adaptation to training and to meet the intense energy demands during competition (21). Due to the large amount of energy expenditure associated with endurance training (42), it may be difficult for these athletes to consume the necessary amount of calories to maintain energy balance. Some female athletes may feel like they have to force-feed themselves to compensate for energy expenditure. Female athletes may believe that a lower weight is the primary predictor of performance, however in high intensity and long duration sports the limiting factor of performance is often energy intake (34).
Furthermore, a particular concern for collegiate athletes is that while they may be able to consume the necessary amount of total calories, the recommended intake of macronutrients may be inadequate (7). Inadequate dietary intake during training, postexercise recovery, and preparation for competition may initiate physiologic processes of underperformance and overtraining. Thyroid hormones have been shown to be substantially lower in female athletes with negative-energy balance induced amenorrhea (31,18). Given that thyroid hormones regulate metabolism and growth, this can have deleterious effects on athletic performance and recovery (19).
Triiodothyronine (T 3 ), thyroxine (T 4 ), and thyrotropin (thyroid stimulating hormone; TSH) have been shown to influence metabolism and growth (6). Thyroid hormone concentrations are reduced with increased exercise training, due to negative energy imbalances and reduced energy availability (32). shown to be decreased after a prolonged, intense training cycle. Interestingly, these decreases remained lower long after the intensified training was reduced (1). These responses should be taken into consideration by coaches and athletes when designing training programs. Thyroid hormone responses to exercise may contribute to, and even exacerbate metabolism and recovery dysfunction in athletes with OT symptoms and energy imbalances. Previous work (28) investigating TH in relation to overtraining have done so over the course of several weeks, and therefore the results of TH must be interpreted cautiously as changes in resting thyroid hormone levels occur slowly, and the process of overtraining may take many months to develop.
Additionally, the relationship of TH to OT has not been studied exclusively during longitudinal studies and therefore more research s needed in this area.
Psychological status in the athlete is of upmost importance, however psychological well being may be reduced when athletes participate during periods of intense training (14) or overtraining (41). Profile of mood states is an accurate and valid test to assess changes or disturbances in mood and vigor (38), however more readily available and faster methods of assessment are needed. Overtrained athletes have decreased motivation, confidence, and vigor (43). Overtrained athletes also have higher ratings of fatigue, depression, anger and compromised concentration (43).
Some of these mood changes have been theorized to be due to endocrine changes (13).
Depression is a commonly cited symptom in hypothyroid individuals and even apparent in subclinical hypothyroid subjects (17). Some investigators suggest the fatigue and depression during overtraining closely resembles symptoms of subclinical hypothyroidism (48). Given the high incidence of depression in OT athletes and altered thyroid function in energy deficient athletes, further investigating TH and psychological status are important factors to consider in monitoring OT.

Demographics
Subject characteristics are presented in Table 2.

Thyroid Hormones:
There were no significant changes in TSH, T 3 , or T 4 from PRE to POST season ( Fig. 1-3 The Δ in TSH from PRE to POST was significantly correlated with a Δ LBM from PRE to POST (ρ=0.571, p=0.041) (Fig. 6).
The percent change (PΔ) in T 3 from PRE to POST was significantly correlated with running performance at the end of the season (ρ=-0.700, p=0.036) (Fig. 4).
There was a non-significant relationship between TSH POST and fatigue POST, although there was a trend (ρ = 0.491, p= 0.063).

Fatigue:
Fatigue was significantly lower at week 2 compared to MID season (p=0.016), week 12 (p=0.018) and POST (p=0.007) (Fig. 8). Fatigue was not statistically different between MID season, week 12 and POST season (p=0.404). There was a significant correlation between fatigue at week 12 and running performance at the end of the season (ρ= -0.741, p= 0.004) (Fig. 7).

Vertical Jump Power:
Vertical jump power significantly increased from PRE to MID in both the middle distance (p=0.036) and long distance runners (p=0.046). However only the middle distance runners significantly decreased power from MID to POST (p=0.018) ( Fig. 9).
There was a significant relationship between lean body mass (PRE and POST) and vertical jump power at PRE (ρ= 0.572, p=0.026) and POST season (ρ=0.802, p=0.001) respectively.
Total caloric intake (kcals) at PRE was not significantly correlated with fatigue at week one, although there was a trend for a relationship (ρ= -0.509, p= 0.053)

Body Composition:
There were no significant changes in body composition from PRE to POST season in the runners overall (Table 2). However, upon further investigation the middle distance runners significantly lost LBM (p=0.028) from PRE to POST (Fig.   10). There were no significant changes in body composition in the long distance runners.

DISCUSSION
The results of this study indicate there were increases in commonly cited symptoms of OT such as decreased anaerobic performance, increased fatigue, and changes in body composition. Additionally, changes in TH were associated with decreased running performance and caloric intake. Thyroid hormones may change too slowly to be used as a convenient and readily available marker of overtraining.
However, monitoring TH may provide valuable information about the training status of an endurance athlete, such that relative decreases or clinically low values may indicate preparedness for competition in championship races at the end of the season.
The use of a weekly fatigue scale and monitoring vertical jump power could be a useful and readily available tool to monitor competitive readiness of an endurance athlete, and therefore may be a promising tool as an early indicator of overtraining.
To our knowledge, this is the first study to use an anaerobic test of vertical jump power as a marker of overtraining in endurance runners. TSH was shown to be higher after an increase in running volume from 48km per week to an increase in 80km per week (2). Interestingly, decreases in T 3 were evident in runners after an increase in running volume of 48km (from baseline) per week, however there were no further decrements in T 3 when increasing running volume to 80km per week (from baseline) (2). Although the current study did not control running mileage throughout the study, most track and field athletes go through a taper performance at the end of the season ( Figure 6). This might be expected as T 3 is the biologically active form of thyroid hormone (47) and has potent effect on metabolism and energy production (4). While it is unclear at the present time if relative decreases in T 3 are responsible for decreases in running performance, it does provide evidence indicating the overall training status of an endurance athlete and readiness to perform well during important times of the season.
Thyroid hormones have been shown to be regulated by energy availability (32) (31). Figure 4 presents data that provide strong evidence to this theory. At the end of the season, lower caloric intake was significantly associated with peripheral thyroid hormone concentrations of T 3 and T 4 , such that the athletes who had consumed more calories also had higher resting levels of thyroid hormones. Furthermore, this relationship was more pronounced when taking into account caloric intake relative to lean body mass (ρ= 0.786, p= 0.021). Thyroxine at POST was significantly associated with total kcals (kcal•kgLBM -1 ) consumed at the end of the season and provides further evidence that circulating thyroid hormones are influenced by not only total calories consumed, but also the consumption relative to lean mass. If relative low availability of energy is one of the primary variables influencing thyroid hormones this may explain the relationship between changes in TSH and changes in LBM ( Figure 5). The strong association between T 4 and caloric intake (kcal•kgLBM -1 ) may influence feedback mechanisms in the hypothalamus to alter thyroid hormone secretion. The relationship seen in Figure 5 indicates that an increase in TSH is associated with an increase in LBM, and a suppression of TSH secretion was seen in those athletes with losses in LBM. It is unclear which order of events are related to the decrease in LBM: decrease in kcal availability; leads to a decrease in T 4 ; which signals the hypothalamus to decrease TSH; therefore conserving energy by further reducing metabolic rate (10) and peripheral hormones to attenuate losses in LBM.
Alternatively, a decrease in kcal availability; could signal the hypothalamus to decrease TSH; which leads to a decrease in T 4 ; therefore conserving energy by further reducing metabolic rate (10) and peripheral hormones to attenuate losses in LBM.
More research is needed to elucidate regulating mechanisms behind these relationships, but it is clear that nutritional intake and thyroid hormones are strongly implicated in an endurance athlete's performance and body composition at the end of a track and field season.
Intakes of some selected nutrients in these athletes were substantially below current recommendations for endurance athletes (44). Although the athletes were meeting recommended macronutrient ratios for exercise (PRE: protein: 15%, carbohydrate: 56%, fat: 30%; POST: protein: 16%, carbohydrate: 54%, fat: 30%), the total caloric intake recommended for their sporting activity was below optimal. It is important to note that in energy deficient states the importance of protein intake increases possibly by increasing availability circulating amino acids (16) for fuel as opposed to initiating gluconeogenesis from valuable muscle tissue. This evidence corroborates previous work that female athletes are in a state of chronic energy deficiency (34) and may increase the risk of developing amenorrhea . Amenorrhea is a common problem in highly active females and is an important cofactor in the female athlete triad (39). The cessation of menstrual function may be a potential indicator of overtraining and decrements in athletic performance (10). An increasing body of evidence suggests energy imbalance may play a significant role in menstrual dysfunction in exercising female athletes (10). While total caloric intake increased from PRE to POST the athletes were not consuming energy intakes to meet the demands of their sport. Carbohydrate intake is one of the most important macronutrient involved in endurance exercise. Increasing carbohydrate intake has also been shown to decrease the severity of overtraining symptoms but not delay its onset of development (18). This is of particular concern for the middle distance runners in our study There was a significant relationship between caloric intake (kcal•kgLBM -1 ) at PRE and fatigue at week 1. The individuals who were consuming more calories relative to their size had lower ratings of fatigue. This may be expected as higher energy intake during an intense training period can reduce feelings of fatigue (18).
There were significant correlations between vitamin D intake at POST and fatigue at POST. In addition, there was a significant relationship between Δ LBM and Δvitamin-  (36) which is important for stride frequency and strategic positioning during endurance races. Research has shown that athletic training has an impact on vertical jump and power-time curves (8). Furthermore reduced amortization phase of the stretch shortening cycle is related to power output, and more importantly that sprint power activities are important in endurance performance and should be incorporated into endurance training programs (20). Research has also shown that measures of anaerobic performance (vertical jump power) and aerobic capacity (VO 2MAX ) together can influence time to exhaustion in distance runners and that anaerobic jumping power is a vital aspect of endurance performance (23). The impairments in VJP over the course of the season occurred when changes in T 3 and running performance were negatively associated (as T 3 decreased runners ran slower), fatigue was high, and running performance decreased. The use of a simple test such as VJP may be a useful tool to monitor training adaptations and overtraining status in endurance athletes. The use of this methodology warrants further investigation. Due to minute testosterone concentrations in women, GH is one of the most important hormones promoting growth and maintenance of muscle tissue and health (9). Secretion of GH may be impaired with OT (49). Growth hormone regulates muscle growth primarily through feedback mechanisms that stimulate the secretion of insulin-like growth factor-1 (IGF-1) from the liver. The production of IGF-1 from the liver is dependent on the presence of T 3 (35) Hepatic IGF-1 modulates type-1 skeletal muscle fiber maintenance and genomic expression. Endurance training primarily utilizes type-1 fibers due to their high glycolytic capacity, resistance to fatigue, capillary and mitochondrial density (24). While type-1 fibers may be more sensitive to TH, the exposure of TH to type-II skeletal muscle fibers results in a stronger, faster and more glycolytic muscle (48).
Monitoring TH in relation to skeletal muscle performance, recovery, and body composition is important to understanding their role in overtrained athletes as well. In our investigation, the middle distance runners significantly lost LBM, decreased VJP, and also ha stale performance at the end of the season. Monitoring anaerobic power may be a useful tool when monitoring performance and overtraining in middle distance runners.
Fatigue was higher at the end of the season than at the beginning. This cohort had previously complained of "dead legs" and high fatigue during past seasons as well as during the season this investigation took place. Elevations in fatigue are expected when training loads are increased (15). Statistical analysis indicated there were no differences in fatigue during the final 4-5 weeks of the season. While there were no differences between these weeks it is important to note that the mean fatigue scores varied between 3.5 (moderate fatigue) and 5 (heavy fatigue). Some of the athletes maintained moderate to heavy fatigue during the final 5weeks of the season, which also happened to be the most important because of conference and regional championships during that time. Intensification of fatigue was also evident despite the coach implementing a taper at the end of the season. These data indicate that persistent feelings of fatigue can also exist despite at taper. This may have been caused which reported reduced energy metabolism, decreased Type-II fibers, and exercise intolerance (45). The runners in our study had similar symptoms of fatigue and may be related to the aforementioned consequences of reduced TH concentration.

Limitations
In the current investigation there were several limitations. Not obtaining a third measurement of thyroid hormones at MID was a limitation. It is well accepted that resting levels of thyroid hormones change slowly and do not occur frequently. Scale X X X X X X X X X X X X X X X Race Times X X X X X X X X X X X X X X X Food Records X X FIGURES Figure 1.

Scope
The goal of athletic training is to improve athletic performance. Athletes train over many weeks or months to elicit sport specific changes and improve performance.
This relationship of duration and intensity exist upon a continuum such that too high of an intensity for too long a duration, without an appropriate amount of rest may lead to increased fatigue and decreased performance of an athlete. Conversely, exercise that does not meet sufficient intensity or duration will not result in physiologic changes to improve sport performance. Athletes and coaches design training programs to prepare athletes to attain peak performances in competition many weeks or months in the future. However, the exercise variables of the training paradigm must be meticulously coordinated according to the athletes' goals and recovery status.
Overtraining syndrome (OTS) in athletes, is often described as decreased performance, hypothalamic imbalances, high fatigue, depression, and altered energy consumption (63). Often times many weeks or months of recovery are needed to see improved performance (78). Research on overtraining has sought to determine the primary causes of this syndrome, so changes in training can be made before the syndrome occurs in the athlete. The problem with overtraining research is that there are a plethora of factors involved in athletic performance (40), and pinpointing the exact cause often leads researchers with more questions than answers in elucidating

Relevance
Monitoring and preventing overtraining is clinically relevant as up to 64% of elite runners report of experiencing at least one episode of OTS at some point in their careers (39,41,42). The prevalence of OTS in younger athletes is also of concern. A recent survey in three-hundred young English athletes indicated that 29% had Functional Overreaching (FOR) is used for a temporary decrease in performance following overload training. This overload is be used by athletes in order to reach an increase in sports specific performance after a short recovery period.
Non-Functional Overreaching (NFOR) occurs when the overload training has detrimental effects in the long term, and full recovery does not happen during the preplanned recovery period.
Overtraining Syndrome (OTS) takes the definition of OT further and incorporates ''syndrome,'' by emphasizing that chronic underperformance is a multifactorial etiology and that the exercise training is not necessarily the only contributory factor of the syndrome (49).

Energy Balance
Nutritional intake is an integral piece of sports training that must be consistently monitored and adjusted in order to achieve training goals, as well as optimal performance during competition (9). Appropriate macronutrient intake is essential to elicit positive adaptation to training and to meet the intense energy demands during competition (29). While endurance performance primarily utilizes aerobic metabolism to meet the demands of exercise, there are situations in long distance events where anaerobic metabolism is necessary to perform optimally (9).
The consumption of CHO during exercise is dependent on the intensity of the exercise being performed (67). As the intensity of exercise increases, the demand for CHO in energy production increases concomitantly (36). When muscle glycogen and circulating blood glucose are diminished, glucose is synthesized from non-CHO sources via gluconeogenesis. Although rare, in such a case, amino acids can be catabolized from lean tissue (36). The use of amino acids for energy is not optimal to maintain and improve performance, and in the long-term will result in the degradation of valuable muscle tissue. For this reason appropriate carbohydrate (CHO), protein (PRO), and lipids must be carefully attuned for each athlete such that energy balance is sustained.
Energy balance is when energy expenditure is equal to energy intake. Due to the large amount of energy expenditure associated with endurance training (62), it may be difficult for these athletes to consume the necessary amount of calories to maintain energy balance. Furthermore, a particular concern for collegiate athletes is that while they may be able to consume the necessary amount of total calories, the recommended intake of macronutrients may be inadequate (15). Indeed, Drenowatz et al. (18) investigated dietary intakes of 15 male endurance athletes during two non-consecutive weeks of high and low volume training. The results of that study indicated that there was no change in energy intake during a high-volume training period, such that energy intakes during the two training periods were similar. Since there were no changes in body composition, the investigators attributed the reported decreased energy intake during the high-volume training as underreporting. One week of increased volume may not be long enough to see significant changes in body composition. Despite the suspected underreporting, the investigators did note that carbohydrate intake was substantially lower than the current recommendations. A review by Hawley et al. (29) suggested that many athletes have carbohydrate deficient diets. The review went on to state that males generally consume enough calories to meet total energy expenditure; females on the other hand consume less energy than what is required from their training. In an excellent review of energy balance in sport and exercise by Loucks, she supported the conclusion that despite the common underreporting by female athletes, females participating in sport are chronically energy deficient (43).
Considering that some theories of the initiation of overtraining stems from energy imbalance or carbohydrate deficiency, the remaining information in this section will review research in investigations related to nutritional intake and overtraining/ overreaching.

Carbohydrates
Prolonged training can result in decreased muscle glycogen levels after successive exercise sessions (16). Recently, it is thought that the fatigue and impaired performance from overtraining may originate from chronically low muscle glycogen (69), however this theory has yet to be fully elucidated in practice. The importance of carbohydrate consumption has been shown to influence the symptoms of overtraining. The current recommended daily allowance for non exercising individuals is 0.8g/kg of body weight (70). However for athletes, and particularly endurance athletes this recommendation is not adequate to maintain nitrogen balance (72). Thus, higher intakes of protein by endurance athletes are necessary to maintain performance and positive adaptation to training. Increased energy expenditure by endurance athletes provides an opportunity for a state of energy imbalance to occur, particularly during periods of high training volume or intensity (18). It is widely accepted that postexercise nutrition is essential for positive adaptation and forthcoming performances in both endurance and strength athletes (70). As demonstrated in the previous section, adequate carbohydrate intake is essential for endurance performance. Acknowledging that information, more importance on increasing protein consumption should be emphasized as well and the importance of "making room" for protein in endurance athletes' diet warrants further discussion (64).
Protein synthesis is strongly associated to the recovery period that is allotted to the athlete post exercise. Aerobic exercise increases protein turnover by the degradation and synthesis of muscle proteins during the recovery of exercise (66).
Although there is some debate as to the inclusion of protein to CHO training supplements (3), the importance of consuming protein post-exercise is widely accepted (70) to repair damaged muscle tissues and possibly the increased preparation for subsequent bouts of exercise (21). Considering many endurance athletes may not be attaining optimal energy balance during the course of training, physiological mechanisms of adaptation may be impaired due to inadequate protein consumption. fractional synthetic rate was decreased 19% with as little as a 20% decrease in total energy intake over ten days. The down regulation of muscle fractional synthesis rate and signaling proteins provide evidence at being in a state of energy deficiency will also reduce the athlete's ability to repair and synthesis muscle tissue in vivo. Even athletes with 60% of daily required energy intake have been shown to attenuate losses in lean muscle tissue by increasing the proportion of protein in the diet (51).
Considering that many endurance athletes are in a state energy deficiency it is important for coaches and athletes to ensure that they are meeting energy requirements from training, and to emphasize the importance of appropriate protein intake.
Furthermore, those athletes who are in energy balance and acquiring protein intakes above the RDA of .8g/kg•BM -1 but within the macronutrient range will gain an added benefit of training as increased protein intake also utilized for energy to maintain blood glucose if the athlete does not consume appropriate amounts of CHO for a given training session (57).
While whole body protein turnover is not necessarily predictive of protein

Hormonal Imbalance
Overtraining is common in endurance sports. The mechanisms responsible for overtraining are difficult to identify, however energy imbalance, hypothalamic imbalances, and autonomic neuromuscular fatigue are important factors (37). Once at the thyroid gland, TSH signals the thyroid to release thyroxine (T 4 ), and to a lesser degree, triiodothyronine (T 3 ). When the levels of T 4 and T 3 in circulation reach a threshold, the secretion of TRH from the hypothalamus subsides and therefore halts the release of TH form the thyroid (20).
While T 4 is the produced in much greater quantities than T 3 , T 3 is considered more biologically potent (1) because it has a higher affinity of binding with thyroid receptors (TR). Thyroxine is considered a pro-hormone, such that T 4 is necessary for the production of T 3 , and also a storage form of the biologically active T 3 . Circulating (D1) and type 2 (D2) activates the deiodination of T 4 into T 3 (1). A third type (D3) of deiodinase is generally seen as an inactivating enzyme that inactivates iodothyronines, such that the deiodination of T 4 by D3 results in the synthesis of reverse T 3 (rT3). No metabolic effects have been cited in reference to r T 3 , therefore many consider that r T 3 is an inactive metabolite (59), although this is still under some debate (77). Since the conversion of T 4 to T 3 can occur in in central and peripheral systems, and is under regulation of specific enzymes and receptors, the control of thyroid hormones represents a tightly regulated system. Because of this, the activity of T 3 , and thus TH signaling, can be mediated within localized tissues and cells, independently of circulating T 3 levels (77).
Thyroid hormones have a profound effect on the growth and metabolism of human physiology. In particular, THs have been shown to influence the rate of heat production, cellular respiration, and metabolic rate via mitochondria, muscle fiber type synthesis and differentiation. While some of the previously mention characteristics of TH action have been known for quite some time, new technology and research techniques have shed light on some of the proposed mechanisms of action in these hormones (73).

Mitochondria
Adenosine tri-phosphate (ATP) is the form of energy that sustains life, and is required for almost all of aspects of physiology such as cell signaling, human locomotion, energy production. Mitochondria produce ATP through the oxidative phosphorylation of various metabolic fuels and substrates (13). Up to 90% of the energy contributed to the cells are produced by the mitochondria. In addition, these organelles are the powerhouses to many of the essential mechanisms that are required during metabolism (14). Because of altered metabolism frequently seen in hypothyroid and hyperthyroid individuals, thyroid hormones became implicated in their role in regulating metabolism and mitochondrial function. Today, it is well known that one of the effects of TH is mitochondrial biogenesis, thereby increasing the number of mitochondria in the cell and increasing the amount of ATP capable of being produced. The mechanisms behind the increase, and the effects TH have on energetics still require more research to be fully understood (13). However, it is believed T 3 may regulate transcriptional pathways of mitochondria, which would harmonize the production of additional mitochondria and events taking place at the nucleus of the cell (14).

Metabolic rate
The proton flux across the inner mitochondrial membrane usually results in the synthesis if ATP. However, this event is never perfect and protons that go un-coupled during phosphorylation across the membrane are dissipated as heat. Through this process, it is believed that basal metabolic rate (BMR) and thermogenesis are regulated (34). Un-coupling proteins were first discovered in brown adipose tissue (BAT). These proteins increase the permeability of the inner mitochondrial membrane and allow protons to escape the gradient and go un-coupled, thus leading to an increase in heat production (7). Brown adipose tissue is abundant in un-coupling protein-1 (UCP-1), and the discovery was made that the activation of these proteins were amplified when stimulated by THs (77). A third type of un-coupling protein (UCP-3) was found predominantly located in muscle and may have implications in human performance (17). Given that muscle is highly active, and the discovery of this protein in the muscle, this has led researchers to consider this an alternative mediator of metabolic rate through thyroid hormones (14). While data does support the role thyroid hormones play in metabolic rate, much of the research on this area is done in hypothyroid, and hyperthyroid human and animal models. There is still some debate in the degree each of these components play in overall metabolic rate in euthyroid individuals (34).

Fiber-type distribution
Evidence suggests THs are important and potent mediators of muscle development and myogenesis (11). Several studies in animal models have provided evidence of the influence TH have in muscle fiber-type differentiation (10,11,12).
The plasticity of muscle fiber types being augmented through exercise is well known (23). The exact mechanisms however, remain to be elucidated. Due to the diverse effects THs have in various tissues, animal models provide the opportunity to control for confounding factors that contribute to muscle fiber adaptations, particularly in humans. Slow (type-1) and fast (type-2) twitch muscle fibers possess distinct metabolic and contractile properties that exist along a continuum. Slow twitch fibers are low force producing fibers but are highly resistant to fatigue, predominantly due to their high capillary density, mitochondrial content, and glycolytic enzymes (32). Fast twitch fibers are high force producing fibers, but fatigue quickly. Casas et al. provided evidence that THs influence fiber-type expression at the mitochondrial membrane.
The investigators overexpressed the mitochondrial T 3 receptor p43 on the mitochondrial membrane in genetically modified mice. The results of that study indicated that at the overexpression of these receptors and T 3 stimulated mitochondrial activity the fibers containing the overexpression and had transitioned to more oxidative slow type fibers (12). The increased receptor content transition was due to amplified mitochondrial biogenesis, respiration, and body temperature in the affected mice. Conversely, Larsson et al induced hyperthyroidism in mice with repeated administration of T 3 (39), and induced increases in a transition from slow twitch fibers to fast twitch fibers. The researchers concluded that four weeks of T 3 administration reduced contraction time and relaxation times by up to 57% and decreased type-1 fibers by up to 77% in the soleus muscle in experimental condition rats. Together these results indicate that THs can change muscle fiber types radically.
Although the methodology between the two studies are different, practically these results may have implications in athletic performance due to the necessity of muscle and metabolism to meet the sport specific demands during exercise and competition.

Thyroid Hormones and Exercise: Descriptive Studies
The influence of thyroid hormones on metabolism and mitochondrial function is widely recognized. Variations in thyroid status have been reported in runners (5,6) and some suggest that the complaint of fatigue and decreased performance may present a sign of subclinical or overt thyroid disease (20).  (60). The investigators explored these resting differences between highly trained male athletes (n=27) and sedentary controls (n=27). In this study TSH was significantly lower in athletes compared to controls.
The although total T 3 was not different between athletes and controls, leptin and the TSH/f T 3 ratio was reduced in highly trained athletes, an indication that feedback mechanisms and regulation of other metabolism hormones influence the availability and relationship of thyroid hormone secretion and activity (60). Again, this study did not screen for dietary intake, and as such, these data must me interpreted cautiously.
A multitude of studies have investigated thyroid hormones in relation to amenorrhea (30,41,42), the cessation of menstrual function may be a potential indicator of overtraining and decrements in athletic performance (19). An increasing body of evidence suggests the energy balance plays a significant role in menstrual dysfunction in exercising female athletes (19). Thong  Whether it be training, or inadequate dietary intake, alterations in these hormones occur in athletes and therefore may influence performance and subsequent overtraining. The culmination of acute training responses eventually leads to chronic adaptations in the training athlete. Therefore, the effect of an acute response of exercise on thyroid hormones requires further discussion.

Prolonged Training and Exercise on Thyroid Hormones
Repeated bouts of maximal aerobic exercise are of occur in regularly practice and competitive meets. Thyroid hormones may be altered by repeated bouts of exercise and subsequent recovery periods. Some research suggests TSH and f T 3 were shown to be decreased after a prolonged (10 weeks), intense training cycle.
Interestingly, these decreases remained lower long after the intensified training was reduced (2). Additionally the changes in thyroid hormones were not present in all the athletes and the investigators indicated that there were responders and non-responders in those that were subject to the intensified training period. These responses should be taken into consideration by coaches and athletes when designing training programs.
These TH responses to exercise may contribute to, and even exacerbate metabolism and recovery dysfunction in athletes with overtraining symptoms and energy imbalances. Furthermore, this study provides evidence that not all athletes respond similarly to a given training program and that there is a large variability in hormonal response to such paradigms. Such variability may be due to current training status, and genetic factors. negligible effects on f T 4 levels (2,55,64).

Body Composition
A euthyroid state of triiodothyronine regulates protein synthesis and some proteolysis (44). However, in both hyper and hypothyroid conditions, T 3 's influence on muscle causes atrophy. Dietary and energy balance dysregulation of TH is of importance, as low TH may negatively affect growth hormone and insulin-like growth factor 1 (IGF-1) secretion (33). The dysregulation of this axis has been shown to result in delayed developmental growth and possibly increased rates of skeletal and muscle injury (33).

Fatigue
Psychological status in the athlete is of upmost importance (63). The profile of mood states (POMS) is an accurate and valid test to assess changes or disturbances in mood and vigor (48). Overtrained athletes have decreased motivation, confidence, and vigor (63). On the contrary, overtrained athletes also have higher ratings of fatigue, depression, anger and compromised concentration (63). Some of these mood changes have been theorized to be due to endocrine changes. O'Conner et al. (56) found that depression and cortisol elevation were highly correlated in overtrained female swimmers however this theory has yet to be fully elucidated. Fatigue and lethargy were experienced by athletes after 10 consecutive days of treadmill exercise to exhaustion (24). Decreases in time to exhaustion and increases in feelings of fatigue and lethargy persisted 5 days after a reduction in exercise and administration of active recovery. Given the influence intensive training programs have on fatigue, mood, and hormonal milieu, employing an effective taper in endurance performance is important for peak performances (79). Similarly recent research has suggested improvements in type II fiber diameter and peak shortening velocity and power after an effective taper without any adverse influences on aerobic capacity (45)

Description of the project:
You have been asked to take part in the study that will attempt to identify and integrate many factors that influence 'calories-in and calories-out' during your regular training and competitive season. The purpose of the study is to understand how this calorie balance might impact health and performance. Tests include blood collection, treadmill exercise testing, daily physical activity, body composition, questionnaires and nutritional factors. The specific objective of the study is to compare your calorie balance and things that might influence it during the early, mid-, and late seasonal phase.

Exclusion criteria:
Taking drugs that act as performance enhancers or interfere with the validity or reliability of information collected in this study will exclude participation in the study. Pregnant women or nursing will also be excluded for participation.

What will be done:
If you decide to take part in this study here is what will happen: Some tests will be conducted at all three phases of the season, and some only during early and late phases.
The following tests will be conducted during a visit at early phase only.
• VO 2 max (~20-30minutes)-For this test we will ask you to run on a treadmill at 6-8 mph for 4 minutes at a 0% grade. After 4 minutes, the grade will be increased to 4% for 2 minutes. The grade will then be increased 2% every w minutes until the you can't run and more.
The following tests will be conducted during a visit at early and late phases only. For these visits you will need to abstain from eating and exercising for 12 hours, and report to the Human Performance Laboratory (Suite P, Independence Square) in the morning: • Blood Collection (~5 minutes) -Approximate 30 ml of blood (approximately 2 tablespoons of blood) will be collected during each of the 3 to 5 visits. A certified health professional will take a blood sample. The blood sample will be used to assess iron levels and some hormones associated with calorie balance (thyroid, cortisol, growth hormone). • Body Composition (20-30 minutes) -Following a height, weight, and waist circumference measurements, your body fat and muscle content will be determined using dual-energy x-ray absorptiometry (iDXA) using fan-beam technology (GE Lunar iDXA, Madison, WI) operated by a certified health professional. DEXA uses two low energy x-rays which scan the body and determine body composition, including bone mineral density. Even though the DEXA uses two x-rays the energy of the x-rays is very low, and radiation exposure is significantly lower than a typical x-ray. The amount of radiation you will be exposed to on each visit is comparable to visiting New York City for a day, and is slightly less than a normal chest x-ray. Even though the DEXA emits only small amounts of radiation, as a precaution often used with x-ray testing, women who are pregnant may not participate to prevent harm to the fetus. For that reason, we have to ask you to give us a urine sample in the labto do a pregnancy test, even if you don't think you need one.
For the DEXA scan, you will be asked to change into a set of medical scrubs, and lay flat on the DEXA panel. A strap will be placed around your ankles to aid in maintaining proper body position during the scan. You will lay as still as possible while an arm which emits the x-rays passes over your body and scans it. A typical DEXA scan lasts approximately 10 minutes.
The following tests will be conducted at all three phases (early, mid, late): • Vertical Jump (10 minutes): We will want to measure how high you can jump. Before you do these exercises, you can warm-up on a stationary bike and do some dynamic stretches. To measure jump height and power, we will ask you to perform 3 jumps in a row as high and as fast as you can on a platform that will record your power and jump height. We will ask you to do that 3 times, resting in between each 3-jump set, so we can use your best scores. • Assessment/Survey Forms -You be asked to complete the following forms: o Food Record -You will be instructed on how to complete an accurate food record, and take with you a 3-day dietary record (2 weekdays and 1 weekend day) form, used to fill out the foods and beverages that you consume. Each 3-day dietary record should take a total of approximately 10 minutes a day.
o Fatigue, stress, and sleep quality questionnaires -you will be asked to fill out questionnaires that attempt to determine your levels of fatigue, stress, and sleep quality. These questionnaires take between 8 -12 minutes to complete. • Physical Activity -You will be asked to wear a monitor (accelerometer) to measure physical activity during waking hours for 5-7 days. You will record when you wore it in your exercise dairy.
The following tests will be conducted at various times throughout the study: • Training & Performance Log -The training dairy will be used to track your workouts and competitions. For any meets you compete in you will record the events you participated in and your times. You can fill this out at home, during the competitions or at the workouts. The activity log takes 5 -10 minutes each time you fill it out.
• Body temperature and heart rate (5 minutes): We are going to ask you to take your temperature with an oral thermometer (which we will give you) and your heart rate (beats per minute) for 30 seconds measured by wrist palpitation first thing in the morning. We will ask you to do this before you get out of bed, so it is as close to resting measurements as possible. We will ask you to do these measurements for the duration of the study. After you take these measurements, we will ask you to write them down in a log for us. • Fatigue, stress, and sleep quality questionnaires: You will be asked to fill out questionnaires that attempt to determine your levels of fatigue, stress, and sleep quality once a week. These questionnaires take between 8 -12 minutes to complete.
• Phone Calls -Prior to each visit you will receive phone calls from a researcher who will set up your assessment date and agenda.

Risks or discomfort:
No known risks or discomforts have been identified for responding to the questionnaires, measuring height, weight, body temperature, heart rate, diet or physical activity.
There are some risks to having bone density tested because a DEXA uses a similar kind of radiation that an x--ray does. Total radiation exposure for the whole study (one DEXA before and after the study) is almost the same as one and a half chest x--rays or four cross--country flights The blood draw uses a sterile technique performed by an experienced clinician. However, there are a few risks with a blood draw that include bruising, formation of a clot, infection, and discomfort from the needle. Fainting is also considered a risk factor during blood collection.
As with regular exercise, there is a slight risk of muscular injury in performing the vertical jump test and VO 2max tests. However, these risks are minimal, and are not greater than what would incur during your normal training routine.

Benefits of this study:
You will gain general knowledge regarding nutrition, sleep patterns, body composition, and physiological and blood measurements that affect performance. You will also gain knowledge about your diet and nutrition, body composition, blood and physiological and blood measurements that, blended with the general knowledge may benefit your performance. In addition, you will not be charged for any of the tests that we ask you to perform.

Confidentiality:
Your participation in this study is confidential. None of the information will identify you by name. Your name will not be linked to any study data or anyone except the principal investigators of this study. None of the study data will be known to anyone except the primary investigators (Dr.'s Hatfield, Melanson, Reibe and Justin and Ryan). All study data and consent forms will be kept in a locked file cabinet in the Kinesiology suite (Independence Square building, Suite P, room 221).
Computer-based data will be kept on a password-protected computer (Independence Square building, Suite P, room 221). The researchers will be the only people who have access to these records.

Blood Sample Collection
By signing below you understand that your blood sample and information derived from it may be stored for up to 5 years and may be used for potential future studies by the principal investigators Dr's Hatfield, Melanson, and Reibe, but only in research studies that examine health in endurance athletes. There will be no expected benefit to you from this analysis since you will not be provided with any result or information from your blood test. If any of your blood chemistries are reported to be out-ofnormal range, you will be promptly notified.

Accurately determining portion sizes and amounts
The most accurate way to determine portion size is to weigh and measure foods and beverages using measuring cups and spoons. The following guidelines will assist you in choosing how to describe and measure portion sizes.

Guidelines for describing and measuring foods FOODS MEASURE & DESCRIBE WITH:
Vegetables, fruit cup, pasta, rice, casseroles, measuring cups (c) ice cream, pudding, margarine, and all liquids teaspoons (tsp) including beverages, soups, gravies, salad dressing Tablespoons (Tbs) Any solid food such as meat, cheese or weight in grams (gm) or ounces (oz) frozen entrees Pie, cantaloupe, other melons fraction of the whole (Ex: 1/8 of 9" pie, ¼ of 6" melon) Liquids Fluid ounces or cups

I. "Guesstimating" Guidelines
Since measuring is not always possible or practical, there are times when "guesstimating" will suffice. Use the following guidelines to help you determine portion sizes when you're not able to weigh or measure.
• A woman's fist is about a cup. • A man's fist is about 1-1/2 cups.

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The cupped palm of an adult's fist holds about one-half cup. The average cooked chicken breast weighs between 3 and 4 ounces.

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A Kraft American single is a one-ounce slice of cheese.

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The standard slice of bologna is one ounce.

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A package of peanuts that you'd get on an airplane is a one-ounce package.

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A frozen Lender's bagel is two ounces. Most other bagels are three to four ounces.