Hypohydration and fasting are used as means to achieve body mass loss and Ramadan fasting is practised by millions of Muslims as a religious custom. Although both hypohydration and fasting have been studied extensively, the effect of hypohydration and Ramadan style fasting on many aspects of human performance is still unclear. In Chapter 3, the effect of exercise-induced hypohydration on muscle performance was evaluated. The protocol was developed to eliminate masking and exacerbating factors such as changes in muscle glycogen storage, muscle temperature, fatigue and fluid distribution change and acid base status. Muscle strength and endurance decreased due to hypohydration equivalent to 2% of body mass. This suggests that hydration status itself can affect adversely athletes' performance. In Chapter 4, the effect of one day (11 h) of Ramadan style fasting on some aspects of exercise performance during the day was investigated. Participants were tested three times throughout the day: at 7:00 am, 12:00 noon and 7:00 pm. 11 h of Ramadan style fasting decreased body mass by 2.1%. No change was found in exercise performance measurements. The results of this study suggest that this short period of fasting has no measurable effects on performance and/or that any effects are compensated by the circadian rhythm throughout the day. However, most athletes use more intense fasting or several consecutive days of fasting to achieve their weight reduction goal. In Chapter 5, the effect of Ramadan fasting (one month long intermittent fasting) on some aspects of exercise performance of athletes (weight category and non-weight category sports) and recreationally active individuals was studied. Participants were tested before, during (after the first week and in the last week) and after the month of Ramadan. Ramadan style living (involving a change in timing of food intake and sleep pattern) affects most of the anthropometric and physical performance parameters of the athletes and of the recreationally active subjects, with no difference in the pattern of change between groups. Almost all of the differences were recovered a week after the end of fasting. Chapter 6 contains the results of three studies focused on the effects of fasting on cognitive function (study A- breakfast elimination; study B- one day (11 h) of Ramadan style fasting; and study C- one month of Ramadan fasting). Results of these studies make a logical conclusion that fasting has a detrimental effect on memory, reaction time and accuracy of responses. The pattern of the effects showed differences that may be related to various participants' characteristics (age group, gender) and the nature of intervention. In summary, Ramadan style fasting may affect performance of some mental and physical tasks in some, but perhaps not in all individuals.

Heat stress-induced hyperthermia and exercise-induced hypohydration are associated with marked alterations in limb and systemic haemodynamics in humans. However, the mechanisms underlying these alterations their effects on muscle blood flow are not well understood. The present thesis examined whether whole body and local heat stresses increased limb skin and muscle blood flow (Study 1) and whether hypohydration and hyperthermia compromised leg muscle, skin and systemic haemodynamics (Study 2). The effects of heat stress and combined hypohydration and hyperthermia were examined at rest and during mild small muscle mass exercise in humans. The results from Study 1 suggested that heat stress was accompanied by vasodilation in both skeletal muscle and skin vasculatures. Therefore in line with concomitant elevations in blood flow, skeletal muscle and skin vasodilation contribute to increases in leg blood flow and vascular conductance with whole body heat stress. Furthermore, increases in leg muscle and skin blood flow with isolated elevations in leg tissue temperature accounted for at least one half of the total increase in leg blood flow with whole body heat stress. Enhanced leg blood flow owed to a net vasodilation as explained by an elevation in vasodilator activity that exceeded increases in vasoconstrictor activity. This phenomenon was closely related to increases in muscle temperature and intravascular adenosine triphosphate (ATP). The results from Study 2 demonstrated that mild and moderate hypohydration and hyperthermia do not compromise leg muscle and skin blood flow or cardiac output at rest or during mild exercise in humans. Furthermore, acute rehydration did not alter leg muscle and skin blood flow or cardiac output compared to hypohydration and hyperthermia despite large alterations in blood volume and haematological variables and the restoration of core temperature. Taken together, the findings of this thesis indicate that: 1) heat stress induces vasodilation in both skeletal muscle and cutaneous vasculature, 2) elevations in muscle temperature and intravascular ATP play a role in heat stress- and exercise-induced hyperaemia, and 3) moderate hypohydrationinduced hypovolemia and haemoconcentration and rehydration-induced hypervolaemia and haemodilution do not alter leg blood flow or cardiac output at rest and during low intensity exercise in humans when a large cardiovascular reserve is available.

Fluid intake and regulation are implicated in the control of energy balance and appetite. The studies in this thesis have examined the effects of fluid manipulation on appetite and energy intake. Fifty-eight young, predominantly Caucasian males were recruited to five studies. The age, height and body mass of the subjects were: 24.9 ± 3.8 y, 1.79 ± 0.1 m, 80.1 ± 14.8 kg (mean ± SD) respectively. In Chapter 3, 13 h of hypohydration after exercise in the heat did not influence energy intake at an ad-libitum buffet meal (P=0.436) compared to a euhydrated trial, although greater thirst (P < 0.001) and lower fullness (P < 0.01) was reported in the hypohydration trial. Chapter 4 demonstrated that there was no difference in energy intake or appetite after 24 h of hypohydration either with or without fluid during a semi-solid ad-libitum breakfast. Thirst and fluid intake were greater during the hypohydrated with fluid (HYPO-F; 618 (251) mL) than the euhydrated with fluid (EU-F; 400 (247) mL) trials (P < 0.01). Chapter 5 and 6 showed that a bolus of water (500 mL) immediately before an ad-libitum porridge breakfast reduced energy intake in both healthy and overweight and obese subjects (P < 0.001). The water preload increased fullness and decreased hunger compared to pre-trial in both studies (P < 0.001). In Chapter 7, 75 minutes before an ad-libitum lunch a post-exercise milk (MILK) based drink reduced energy intake (6746 (2035) kJ) compared to an isoenergetic flavoured carbohydrate (CHO) and water based drink (7762 (1921) kJ; 7672 (2005) kJ) (P < 0.05). This thesis has shown that when subjects are hypohydrated, either after exercise or after 24 h of fluid restriction energy intake is not different at an ad-libitum meal. However, there is an increased thirst and subsequent fluid intake before an ad-libitum meal (chapter 3 and 4). This effect was more acutely displayed when a bolus of water was provided immediately before an ad-libitum breakfast meal and subsequently decreased energy intake in both normal and overweight/ obese subjects (chapter 5 and 6). The possible mechanism for this was gastric fill and distension creating satiety before a meal. Chapter 7 has showed that when subjects consume isoenergetic drinks with different energy densities (milk vs CHO and water), before an ad-libitum lunch, energy intake was decreased when milk was consumed. Milk having an increased energy density due to larger protein fractions (casein) may further explain the decrease in energy intake found in chapters 5 and 6 by a similar mechanism. Therefore, gastric fill before a meal decreases ad-libitum energy intake by either the intake of water immediately before a meal or by milk as a more delayed response (75 min). The hydration status however, did not affect energy intake directly in our finding, although it did affect subsequent fluid ingestion, which may have affected findings in chapters 3 and 4.

It is known that during fluid restriction, obligatory water losses continue and hypohydration develops and that restricted energy intake leads to a concomitant restriction of all other dietary components, as well as hypohydration, but the specific effects of periods of fluid and/ or energy restriction on fluid balance, electrolyte balance and exercise performance have not been systematically described in the scientific literature. There were two main aims of this thesis. Firstly, to describe the effects of periods of severe fluid and/ or energy restriction on fluid and electrolyte balance; secondly, to determine the effect of electrolyte supplementation during and after energy restriction on fluid and electrolyte balance as well as energy exercise performance. The severe restriction of fluid and/ or energy intake over a 24 h period all resulted in body mass loss (BML) and hypohydration, but whilst serum osmolality increases during fluid restriction (hypertonic hypohydration), serum osmolality does not change during energy restriction (isotonic hypohydration), despite similar reductions in plasma volume (Chapter 3). These differences in the tonicity of the hypohydration developed are most likely explainable by differences in electrolyte balance, with fluid restriction resulting in no change in electrolyte balance over 24 h (Chapter 3) and energy restriction (with or without fluid restriction) producing significant reductions in electrolyte balance by 24 h (Chapter 3; Chapter 4; Chapter 5; Chapter 6; Chapter 7). Twenty four hour combined fluid and energy restriction results in large negative balances of both sodium and potassium, and whilst the addition of sodium chloride to a rehydration solution ingested after fluid and energy restriction increases drink retention, the addition of potassium chloride to a rehydration solution does not (Chapter 4). Supplementation of sodium chloride and potassium chloride during periods of severe energy restriction reduces the BML observed during energy restriction and maintains plasma volume at pre-energy restriction levels (Chapter 5; Chapter 6; Chapter 7). iv These responses to electrolyte supplementation during energy restriction appear to be related to better maintenance of serum osmolality and electrolyte concentrations and a consequential reduction in urine output (Chapter 5; Chapter 6; Chapter 7). Additionally, 48 h energy restriction resulted in a reduction in exercise capacity in a hot environment and an increase in heart rate and core temperature during exercise, compared to a control trial providing adequate energy intake. Whilst electrolyte supplementation during the same 48 h period of energy restriction prevented these increases in heart rate and core temperature and exercise capacity was not different from the control trial Chapter 8). In conclusion, 24-48 h energy restriction results in large losses of sodium, potassium and chloride in urine and a large reduction in body mass and plasma volume and supplementation of these electrolytes during energy restriction reduces urine output, attenuates the reduction in body mass and maintains plasma volume and exercise capacity.

The aim of this study was to measure the degree of dehydration experienced during surf practice and examine the effect this might have on surfing performance, cognitive function and muscular endurance of elite surfers. Twelve male national and international level surfers volunteered to take part in the study. Their mean (± SD) age, body mass, height and surfing experience were 27.0 ± 3.3 years, 73.2 ± 7.1 kg, 1.7 ± 0.05 m and 21.0 ± 3.1 years, respectively. The participants were randomly assigned to one of two trials: no fluid ingestion (NF) or fluid ingestion (FI) during 100 min of surf practice in a steamer wetsuit. The experiment was designed to emulate not only the physical and cognitive demands of surfing but also the ambient environment in which it takes place. Before and immediately after surf practice, the participants had their hydration status measured, completed a cognitive test battery and upper and lower-body muscular endurance tests. Surfing performance was assessed during the first and last 20 min of practice. At the conclusion of the NF trial, participants showed a 3.9 ± 0.7% body mass (BM) loss, this was significantly greater (P < 0.05) than the 1.6 ± 0.7% BM loss seen at the end of the FI trial. In the NF trial, surfing performance decreased by 20.3 ± 7.1%, but showed a slight improvement in the FI trial (1.9 ± 10.2%). Of the six cognitive domains assessed (short-term memory, information processing speed, working memory, attention, visuomotor skill and visual acuity) all were significantly impaired when at a 3.9 ± 0.7% BM loss (P < 0.05) yet were unaffected at a 1.6 ± 0.7% BM loss. Information processing speed and working memory were the most strongly correlated to surfing performance (r = 0.74; P < 0.05). At the conclusion of the NF trial upper and lower-body muscular endurance were diminished by 21.2 ± 5.5% and 4.4 ± 5.8%, respectively. At the conclusion of the FI trial upper-body muscular endurance was reduced by 17.0 ± 4.1% while lower-body muscular endurance was marginally better (1 ± 3%). There was a significant difference in muscular endurance capacity between trials yet no significant correlation was observed between muscular endurance and surfing performance. The findings of this study suggest that surf practice for 100 min in a steamer wetsuit results in BM loss severe enough to significantly impair surfing performance, cognitive function and muscular endurance. Yet, when water is consumed during surf practice, surfing performance, cognitive function and lower body (but not upper-body) muscular endurance is maintained. Keywords: fluid ingestion, surf training, steamer wetsuit, hypohydration.

Aim and research questions: The aim of this study was to investigate the effects of rapid weight loss (RLW) in relation to physiological aspects, psychological aspects, and sport specific performance through a systematic review. This study further aimed to investigate what methods are being used when studying the effects of RWL. To examine the above the following research questions have been used: what physiological and psychological effects can be found in concurrence with RWL, how does the effects of RWL impact sports performance, and what methods are recurrently being used when studying the effects of RWL? Method: For this purpose a systematic review was conducted using three databases; PubMed, Cochrane Library, and SPORTDiscus. Out of 1163 screened articles 20 of them were included in the review. Further analysis was conducted using Forsberg &amp; Wengströms quality evaluation for quantitative studies screening form and the Swedish agency for health technology assessment and assessment of social services Risk of systematic bias screening form. Results were later summarized and compiled. Result: The most evident finding was that the athletes suffer from dehydration with significantly elevated levels of Urine Specific Gravity, USG. In addition the utilization of RWL also have a negative impact on both cognitive functions and mood, it affects important central factors such as reaction time. However many of the negative physiological effects have been show to subside after 4-12 hours if adequate recovery measures are implemented. The foremost evident sport specific finding was a maintained or increased relative anaerobic peak power. Furthermore positive results in maintaining performance for factors such as; Counter Movement-Jump, clean, snatch, judo specific test, and balance test. Conclusion: Although athletes were found dehydrated performance was still maintained in sport specific factors. However, this systematic review also found an overall lack of quality within the studies conducted. Sufficient scientific evidence was not found to draw reliable conclusions, additional studies of higher quality are needed for future reviews. / Syfte och frågeställningar: Studiens syfte var att göra en systematisk granskning kring effekterna av snabb viktreducering (RWL) kopplat till fysiologiska aspekter, psykologiska aspekter, och idrottsspecifik prestation. Studien strävar sedermera efter att undersöka vilka metoder som vanligtvis används för att studera RWL. För detta användes följande frågeställningar: Vilka fysiologiska och psykologiska effekter kan påträffas i samband med RWL, samt hur påverkar effekter av RWL idrottsprestation, vilka metoder används återkommande för att studera effekterna av RWL? Metod: En systematisk granskning har utförts i tre databaser: PubMed, Cochrane Librairy, och SPORTDiscus. Utav 1163 screenade artiklar inkluderades 20 stycken i granskningen. Vidare analys bedrevs med Forsberg &amp; Wengströms kvalitetsgranskning för kvantitativa studier-formulär samt Statens beredning för medicinsk och social utvärderings Risk för systematisk bias-formulär. Resultaten summerades sedan och sammanställdes. Resultat: Det tydligaste resultatet var att idrottarna lider av uttorkning och signifikant förhöjda nivåer av Urine Specific Gravity, USG. Dessutom har nyttjandet av RWL negativ inverkan på både kognitiva funktioner och humör, det påverkar viktiga centrala faktorer som reaktionstid. Däremot har många av de negativa fysiologiska faktorerna avtagit efter 4-12 timmar om adekvata återhämtningsmetoder implementerats. Det främsta idrottsspecifika fyndet var en bibehållen relativ anaerob peak power. Därutöver syntes fler positiva resultat bibehållen prestation hos faktorer såsom; counter movement-jump, frivändningar, ryck, judospecifika tester, och balanstester. Slutsats: Trots att utövarna var dehydrerade bibehölls prestation i sportspecifika faktorer. Denna systematiska granskning fann emellertid också en övergripande bristande kvalitet inom de genomförda studierna. Tillräckliga vetenskaplig evidens har inte visat för att konkludera tillförlitliga slutsatser, ytterligare studier av högre kvalitet behövs för framtida granskningar.