Forsyth Jacky J, Reilly Thomas
Sport and Exercise Sciences, North East Wales Institute of Higher Education, Plas Coch, Mold Road, Wrexham, Wales, UK.
Med Sci Sports Exerc. 2005 Dec;37(12):2046-53. doi: 10.1249/01.mss.0000179094.47765.d0.
This study examined the isolated and combined effects of time of day and menstrual cycle phase on the determination of the lactate threshold (Tlac) and blood lactate concentration.
Eleven endurance-trained female athletes (mean age 32.4+/- 6.9 yr) were tested at 06:00 and 18:00 h and at two phases of the menstrual cycle, the midfollicular phase and the midluteal phase. Capillary blood (25 muL) was obtained from the tip of the toe at rest, and during the last 30 s of a continuous, multistage, 3-min incremental protocol on the Concept II rowing ergometer. To determine Tlac, a curve-fitting procedure (Dmax method), a visual method (Tlac-vis), and the fixed blood lactate concentration of 4.0 mmol.L (Tlac-4 mM) were used. Ventilatory threshold (Tvent) was also determined.
In the midluteal phase of the menstrual cycle, Tlac-4 mM occurred at a significantly higher exercise intensity, heart rate, and oxygen consumption than it did in the midfollicular phase. Blood lactate concentration at Tvent and at Tlac using the Dmax method was significantly lower in the midluteal phase. No significant interaction effects (menstrual cycle x time of day) were observed for any of the methods used to determine Tlac or for values of blood lactate concentration at rest and at maximum.
These findings suggest that, when using fixed values of blood lactate in physiologic assessment, consideration should be given to the menstrual cycle phase in which the test is carried out.
本研究探讨了一天中的时间和月经周期阶段对乳酸阈（Tlac）测定及血乳酸浓度的单独和联合影响。
对11名耐力训练的女性运动员（平均年龄32.4±6.9岁）在06:00和18:00时以及月经周期的两个阶段，即卵泡中期和黄体中期进行测试。在休息时以及在Concept II划船测力计上进行的连续、多阶段、3分钟递增方案的最后30秒，从脚趾尖采集25微升毛细血管血。为了确定Tlac，使用了曲线拟合程序（Dmax法）、视觉方法（Tlac-vis）以及固定血乳酸浓度4.0 mmol/L（Tlac-4 mM）。还测定了通气阈（Tvent）。
在月经周期的黄体中期，Tlac-4 mM出现时的运动强度、心率和耗氧量显著高于卵泡中期。使用Dmax法时，黄体中期Tvent和Tlac时的血乳酸浓度显著更低。对于用于确定Tlac的任何方法以及静息和最大血乳酸浓度值，均未观察到显著的交互作用（月经周期×一天中的时间）。
这些发现表明，在生理评估中使用固定血乳酸值时，应考虑进行测试时的月经周期阶段。
