緒論：網球反覆衝刺能力測驗 (repeated-sprint ability, RSA) 及揮擊與轉向測驗 (hit& turn tennis test, HTT) 主要係評估網球專項之衝刺、敏捷及耐力性等運動表現，目前尚無研究探討咖啡因增補對上述運動表現的影響，本研旨在探討咖啡因增補對網球選手專項體能表現及可能機轉。方法：10 位男性網球甲組選手 (年齡：16.3 ± 0.9 歲；身高：173.2 ± 5.1 公分；體重：63.8 ± 5.9 公斤)，採雙盲、安慰劑控制及平衡次序法進行咖啡因 (6 mg/kg) 或安慰劑處理，並在增補後1 小時依序測量RSA (共10 趟) 及HTT 測驗等網球專項體能表現指標，並在增補前、後進行肘前靜脈 (鈣離子及鉀離子) 及增補前、運動測驗後進行耳尖毛細 (血乳酸) 等血液採集。採相依樣本t-test 考驗不同增補處理在RSAmean、RSAbest、RSAdecrement %與HTTlevel 等專項體能表現，以及二因子變異數分析 (時間x 增補) 在血液生化指標之差異顯著情形，統計水準皆為α = 0.05。結果：相較於安慰劑，增補咖啡因後顯著減少RSAmean 之秒數 (↓3.3%) 與增加HTTlevel 之階數(↑4.9%)，以及降低血鉀濃度 (↓10.8%) 與提升血鈣濃度 (↑2.9%) (p < .05)。結論：6 mg/kg咖啡因增補能降低網球專項體能RSAmean 之秒數，進而提升每趟衝刺平均速度表現，以及延長網球專項耐力表現HTTlevel 之階數。另外，咖啡因增補後能促使循環中鉀離子濃度下降與鈣離子濃度上升，有利於鈉/鉀 ATP 酶活性提升進而延緩肌肉收縮疲勞及增進肌肉收縮能力，此可能為促進本研究表現提升的可能機轉。

Introduction: The repeated-sprint ability (RSA) and hit and turn tennis test (HTT) are used to evaluate the tennis-specific fitness performances in sprinting, agility, and endurance. However, the relationship between caffeine supplementation and tennis-specific fitness performance has not been investigated. This study aimed to investigate the effects of caffeine supplementation on tennis-specific fitness performance in tennis players. Methods: A total of 10 male (age: 16.3 ± 0.9 years; height: 173.2 ± 5.1 cm; body weight: 63.8 ± 5.9 kg) tennis players were recruited. Subjects ingested caffeine (6 mg/kg) or placebo in a double-blind, placebo-controlled, and counter-balanced fashion. The RSA and HTT were assessed 1 hour after supplementation. Blood samples (antecubital vein: Ca++ and K+; ear capillaries: lactate) were obtained before and after supplementation and exercise. A dependent t-test was used to compare tennis-specific performance variables, and a two-way (time × supplement) analysis of variance (ANOVA) was used to compare blood-based variables between the caffeine and placebo conditions. Significance was set at α = 0.05. Results: Compared with placebo, caffeine supplementation significantly reduced the RSAmean (↓3.3%), enhanced HTT (↑4.9%), reduced K+ concentrations (↓10.8%), and increased Ca++ concentration (↑2.9%) (p <.05). Conclusion: Caffeine supplementation at 6 mg/kg facilitates tennis-specific performance, as assessed by RSAmean (↓3.3%) and HTTlevel (↑4.9%). Caffeine-induced performance improvements may be associated with a caffeine-associated decrease in plasma K+ concentrations and increased Ca++ release, resulting in increased Na+/K+ ATPase activity, which might attenuate muscle fatigue and enhance muscle contractile ability.