目的︰探討離心運動誘發肌肉損傷 (EIMD) 後，增補不同劑量之咖啡因對肌肉力量(MVIC)、疲勞 (Tlim) 及肌肉酸痛 (DOMS) 的效應。方法：招募45位男性大學持拍類運動員，採雙盲、安慰劑控制及獨立樣本之設計，依前測之肘屈肌MVIC將受試者隨機分派至安慰劑組 (15名；年齡：22.33 ± 2.09歲) 、低劑量組 (15名；4 mg/kg；年齡：22.46 ± 3.11歲) 及高劑量組 (15位；8mg/kg；年齡：22.60 ± 2.09歲) 。所有受試者先以60下最大等速 (90°s-1) 肘屈肌離心收縮誘發肌肉損傷，接著在EIMD後24與48小時連續2天進行增補，並在增補前及增補後各進行1次肌力測試 {包含肘屈肌MVIC、最大肌電圖訊號 (EMGmax) 及肘屈肌Tlim}，以評估咖啡因對EIMD所引起之肌力流失的效應，同時在肌力測量後並立即進行DOMS指數的收集。另外，在每次肌力測量前、增補後及運動後採血分析血液生化指標 (鉀離子、鈣離子、肌酸激酶、睪固酮、皮質醇) 。統計方法以體重及增補前各依變項數值為共變數，採混合設計2因子共變數分析。結果：所有指標在組別因子及時間因子之交互作用皆未達顯著 (p >.05) 。在組別因子主要效果中，低劑量組之MVIC (0.66 ± 0.20 Nm/kg) 及EMGmax (1207.87 ± 450.98 μV) 皆顯著優於安慰劑組 (MVIC: 0.64 ± 0.15 Nm/kg；EMG: 1051.23 ± 483.48 μV) 與高劑量組 (MVIC: 0.64 ± 0.21 Nm/kg；EMG: 893.76 ± 399.38 μV) ；安慰劑組之DOMS (63.83 ± 18.69 mm) 分別顯著高於高劑量組 (58.33 ± 24.75 mm) 與低劑量組 (43.33 ± 21.10 mm) (p <.05) ；高劑量組之Tlim (95.03 ± 50.42 秒) 顯著高於安慰劑組 (Tlim: 76.43 ± 16.17 秒) (p <.05) ；高劑量組之鉀離子 (3.69 ± 0.60 mmol/L) 及鈣離子 (10.01 ± 0.27 mg/dL) 濃度顯著高於安慰劑組 (鉀離子：4.24 ± 0.65 mmol/L；鈣離子：9.72 ± 0.19 mg/dL) (p <.05)；高劑量組增補後及運動後之T/C ratio (0.025 ± 0.010；0.024 ± 0.015) 顯著低於安慰劑組 (0.034 ± 0.003；0.036 ± 0.010) (p <.05)。結論：每公斤體重4與8毫克的咖啡因增補劑量在EIMD期間對肌力表現恢復及DOMS的減緩並無劑量反應的關係存在。同時低劑量咖啡因增補可有效減緩DOMS並提升運動單位的招募，對促進MVIC的效果較具優勢；高劑量咖啡因則對肌耐力表現Tlim的促進較具優勢，可能原因為增補後Ca++的釋放並減緩血液K+濃度而有利於減緩肌肉疲勞有關。

Purpose: The current study aimed to evaluate the dose-response effects of different doses of caffeine supplementation on muscle strength (MVIC), muscle fatigue (Tlim), and DOMS after eccentric exercise-induced muscle damage. Methods: With a double-blinded, placebo-controlled independent sample design, the present study recruited 45 male college racket sport athletes. College athletes were randomly assigned into placebo, low-dose, and high-dose groups. Muscle damage was firstly induced by prior elbow flexor maximal isokinetic eccentric contraction in every subject. Next, consecutive caffeine supplementations were administered in by each subject 24 hr and 48 hr after EIMD. To investigate the effects of caffeine on EIMD-induced muscle power depletion, strength tests {i.e., elbow flexor MVIC, maximal electromyography (EMGmax) , and elbow flexor Tlim} were performed before and after each supplementation, followed by data collection on DOMS index. Results: No significant group by time interaction was observed across all indices (p >.05). Regarding the main effects of group factor, MVIC (0.66 ± 0.20 Nm/kg) and EMGmax (1207.87 ± 450.98 μV) in the low-dose group were superior as compared with the placebo (MVIC: 0.64 ± 0.15 Nm/kg；EMG: 1051.23 ± 483.48 μV) and high-dose groups (MVIC: 0.64 ± 0.21 Nm/kg；EMG: 893.76 ± 399.38 μV). DOMS was significantly higher in the placebo (63.83 ± 18.69 mm) group as compared with the high-dose (58.33 ± 24.75 mm) and low-dose groups (43.33 ± 21.10 mm) (p >.05). Tlim in the high-dose group (95.03 ± 50.42 sec) was significantly higher than that in the placebo group (Tlim: 76.43 ± 16.17 sec) (p <.05). Levels of K+ (3.69 ± 0.60 mmol/L) and Ca++ (10.01 ± 0.27 mg/dL) were significantly higher in the high-dose group as compared with placebo group (K+: 4.24 ± 0.65 mmol/L；Ca++: 9.72 ± 0.19 mg/dL) (p <.05). T/C ratios at the post-supplement and post-exercise time points (0.025 ± 0.010；0.024 ± 0.015) were lower in the high-dose group as compared with the placebo group (0.034 ± 0.003；0.036 ± 0.010) (p <.05). Conclusion: There was no dose-response relation between caffeine dosage (i.e., 4g/kg, 8g/kg), muscle strength recovery, and DOMS attenuation. Low dosage of caffeine supplement can attenuate DOMS and facilitate recruitment of motor units, which may thereby benefit MVIC performance. High dosage of caffeine supplement may promote Tlim performance, an indicator of muscular endurance, possibly via the attenuation of muscle fatigue induced by the release of Ca++ and decreased serum K+ levels.

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