The aims of this thesis were to; firstly, address the numerous concerns for athletes associated with exercise-induced dehydration and electrolyte loss; secondly, to examine the development of methods of assessing soccer players’ performance; and thirdly, to investigate the inter-relationship between soccer-specific tests. Finally, through a series of studies, the effect of electrolyte loss on subsequent soccer-specific performance was examined. / Chapters 1 and 2 comprise of detailed literature reviews, which introduce the pertinent issues related to hydration, electrolyte loss and assessment of soccer performance and outline areas of necessary future research. Chapter 3 measured the effect of short-term fatigue, through a repeated sprint ability (RSA) test, on subsequent skill performance, via the Loughborough Soccer Passing Test (LSPT), in thirty international level female soccer players. No significant differences were observed in any of the movement, penalty or total time taken to complete the LSPT between the pre- and post-RSA scores. / Chapter 4 investigated the hydration status and electrolyte loss of 14 professional soccer players (mean ± SD; Age: 24.1 ± 3.5 years; Height: 1.78 ± 0.07 m, Body mass (BM): 72.6 ± 12.1 kg) during normal “in-season” training and subsequently examined the effect of beverage sodium (Na⁺) on RSA performance. It was found that RSA performance was significantly improved in professional soccer players by the inclusion of 21.32 mmol·L⁻¹ Na⁺ in a beverage, when compared to a control beverage. / Chapter 5 examined the effects of 60 min of soccer-specific training on LSPT performance, hydration status and core temperature (Tc) when ingesting either a carbohydrate-electrolyte (CHO-E) or control (CON) drink. Seven healthy male soccer players (age: 23 ± 2.9 y, height: 1.7 ± 0.04 m, mass: 62.7 ± 6.7 kg) each completed a carbohydrate-electrolyte (CHO-E) and a control (CON) trial. There was an improvement in movement time (p = .034) and overall LSPT performance (p = .031) post-exercise in CHO-E when compared with CON. No differences were observed in Tc or absolute and relative body mass loss between trials (p> .05). / The final investigation of this thesis is detailed in chapter 6, where the purpose of the investigation was to examine the effect of beverages with different Na⁺ concentrations in soccer players on repeated sprint and soccer skill performance during and after soccer-simulated activity in a hot and humid environment. 12 healthy, male, semi-professional soccer players volunteered for this study (mean ± SD: age 24.5 ± 3.3 y, height 1.8 ± 0.06 m, BM 78.1 ± 9.4 kg). The results highlighted that the RSA performance was improved in both the High-Na⁺ and Na⁺ trials when compared to the CON trial at each time point (p < 0.05). A significant improvement in LSPT performance was observed in the Hi-Na⁺ trial compared with CON trial at all measurement time points (p < 0.05). / The findings from this thesis highlight that the addition of Na⁺ to a beverage can enhance sprint and skill performance in soccer players when the beverage is consumed during sport-specific training in a hot and humid environment. / 本論文的研究目的包括; 首先，探討運動員在運動時脫水和流失電解質的眾多顧慮;其次，考究足球員表現評估方法之發展; 第三，通過一系列的研究，調查電解質流失對隨後足球專項表現的影響。最後，就不同足球專項評估方法的相互關連性進行研究。 / 第1章和第2章包含詳盡的文獻綜述，當中介紹了水合作用、電解質流失和足球員表現評估方法的議題，並帶出未來需要研究的方向。第3章探討透過反复衝刺能力（ RSA ）測試引致的短期疲勞對足球表現的影響。30名國際級女子足球運動員在短期疲勞前後進行LSPT技術測試。結果顯示，RSA前後的LSPT成績 (不論動作、懲罰或總完成時間)均無顯著差異。 / 第4章調查了14名專業足球運動員（平均值±標準差; 年齡： 24.1 ±3.5歲，身高：1.78 ±0.07米，體重（ BM ）：72.6 ±12.1千克）於”比賽季”常規訓練的水合狀態和電解質流失，並隨後研究飲料鈉（Na +）對RSA表現的影響。研究發現， 與對照組相比，運動員飲用包含21.32 mmol.L -1 Na +的飲料後，RSA表現有顯著提升。 / 第5章研究攝入碳水化合物-電解質飲料（ CHO - E）或對照飲料（CON ）後，60分鐘足球專項訓練對LSPT表現，水合狀態和核心溫度（Tc）的影響。七名健康男性足球員（年齡：23 ±2.9歲，高度： 1.7 ±0.04米，體重： 62.7 ±6.7千克）各完成一個碳水化合物-電解質（ CHO - E）和一個對照組（CON ）試驗。與CON組相比，，CHO - E組在運動時間（P = .034 ）和整體LSPT表現（P = .031 ）均有顯著提升。兩組間的Tc或絕對和相對體重流失則無顯著差異（P> 0.05 ）。 / 在最後第6章，本論文研究在高溫高濕環境下的足球模擬活動期間和隨後，不同Na +濃度飲料對足球員的反複衝刺和足球專項技巧表現的影響。 12名健康的男性半職業足球運動員自願參加本研究（平均值±標準差： 24.5 ±3.3歲，身高1.8 ±0.06米，體重78.1 ±9.4千克） 。結果顯示，與CON組相比，高Na +和Na +組在所有測量時間點中的RSA表現都有顯著提高（ P <0.05）。至於LSPT表現，高Na +組則比CON組在所有測量時間點均有顯著改善（ P < 0.05）。 / 綜上所述，本論文的研究結果強調，在飲料添加Na +可提高足球運動員在炎熱和潮濕的環境訓練時的短跑和技術表現。 / O'Reilly, John Timothy. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2014. / Includes bibliographical references (leaves 116-137). / Abstracts also in Chinese. / Title from PDF title page (viewed on 08, November, 2016). / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only.