本研究的目的，在探討長跑選手在臨界速度（ CV ）強度運動時， 血中乳酸濃度 的變化情形，以確認 CV 是跑步有氧運動能力指標的有效性。以國內男性長跑選手 20 名為 對象（年齡為 25.65 ± 8.12 歲、 體重為 60.53 ± 7.92 公斤、身高為 171.35 ± 6.61 公分、最大耗氧量（ VO �� max ）為 63.55 ± 8.03 ml ． kg �笐薄D min �笐薄B換氣閾 值（ AT ）為 49.45 ± 8.78 mlk ． g �笐薄D min �鞦薄^，進行三個不同距離（ 800 、 1500 與 5000 公尺）的跑步最大能力測驗， 再依跑步距離與成績表現呈直線正比關係的計 算模式，分別求出受試者的 CV。接著依平衡次序的方式，分別以 85 ％、100 ％與 115 ％ 的 CV 強度，進行 20 分鐘的固定強度運動測驗；測驗前後分別測量受試者的血中乳酸濃度 ，並依重複量數的共變數統計法進行分析。 研究結果發現，長跑選手 CV （ 4.52 ± 0.28 m/s ）與三個不同距離跑步成績（分別為 2.24 ± 0.15、4.65 ± 0.29 與 17.71 ± 1.06 分鐘）的平均速度皆達顯著相關（分別為 0.51 ± 0.54 與 0.99 ）， VO �� max、 AT 與 5000 公尺跑步平均速度的相關則只有 0.47 （ p<.05 ）與 0.64 （ p<.05 ）。CV 強度跑 步方面， 所有受試者皆能完成 85 ％與 100 ％ CV 強度的 20 分鐘跑步，但是 115 ％ CV 強度的跑步時間則只有 9.13 ± 3.26 分鐘， 三次運動後的血乳酸濃度（分別為 2.32 ± 0.86、6.93 ± 3.47 與 11.38 ± 2.49 mM/L ）皆達顯著差異， 而且以 CV 強度跑步後的 血乳酸濃度有高於 4mM 乳酸閾值的現象。 本研究再一次證實 CV 與長跑運動能力的高度相 關， 但是依血乳酸的反應來看，長跑選手理論上的 CV，顯然比實際血乳酸濃度可以達穩定 狀態的強度高約 15 ％。

　　　　　The purpose of this study was to determine the predictability of critical velocity (CV) upon endurance running potential via the investigation of the effect of blood lactate during 20-min running of the distance runners. The raw data of the distance runners used were 20 males (age 25.65 ± 8.12 yr, weight 60.53 ± 7.92 kg, height 171.35 ± 6.61 cm, VO �荃� max 63.55 ± 8.03 ml ． kg �笐薄D min �笐�, VT 49.45 ± 8.78 ml ． kg �笐薄D min �笐� ). The principle of the relationship between running time and distance was used to calculate CV. The CV of very subject was calculated through his best records of 800m, 1500m and 5000m running. All subjects participated all of the three 20-min exercise tests on treadmill, with the speed 85% CV, 100%CV and 115%CV respectively. The concentration of blood lactate was measured before and after each of the three test. The results were as follows: (1) CV and the average velocity of the best records of 800m, 1500m and 5000m running (2.24 ± 0.15, 4.65 ± 0.29 and 17.71 ± 1.06 min, individually) all were significantly correlated (0.51, 0.54 and 0.99). Furthermore, the correlation between the average velocity of 5000m running, VO �� max and AT were 0.57 (p<.05) and 0.66 (p<.05). (2) When running on 85% CV and 100%CV, all subjects finished running for 20-min, but running on 115% CV, the running time was 9.13 ± 3.26 min olny. (3) The concentration of blood lactate collected after the three tests was significantly different with each other (2.32 ± 0.86, 6.93 ± 3.47 and 11.38 ± 2.49 mM/L) for the distance runners. In conclusion, the higher the CV, the better the endurance running potential for the distance runners. However theoretical CV overestimates the practical running velocity that could maintain blood lactate on a stable condition by about 15%.