University of Lethbridge, AB, Canada.
Acta Physiol (Oxf). 2010 Apr;198(4):477-86. doi: 10.1111/j.1748-1716.2009.02058.x. Epub 2009 Nov 13.
The reduction in cerebral oxygenation (Cox) is associated with the cessation of exercise during constant work rate and incremental tests to exhaustion. Yet in exercises of this nature, ecological validity is limited due to work rate being either fully or partly dictated by the protocol, and it is unknown whether cerebral deoxygenation also occurs during self-paced exercise. Here, we investigated the cerebral haemodynamics during a 5-km running time trial in trained runners.
Rating of perceived exertion (RPE) and surface electromyogram (EMG) of lower limb muscles were recorded every 0.5 km. Changes in Cox (prefrontal lobe) were monitored via near-infrared spectroscopy through concentration changes in oxy- and deoxyhaemoglobin (Delta[O(2)Hb], Delta[HHb]). Changes in total Hb were calculated (Delta[THb] = Delta[O(2)Hb] + Delta[HHb]) and used as an index of change in regional blood volume.
During the trial, RPE increased from 6.6 +/- 0.6 to 19.1 +/- 0.7 indicating maximal exertion. Cox rose from baseline to 2.5 km ( upward arrowDelta[O(2)Hb], upward arrowDelta[HHb], upward arrowDelta[THb]), remained constant between 2.5 and 4.5 km, and fell from 4.5 to 5 km ( downward arrowDelta[O(2)Hb], upward arrowDelta[HHb], <-->Delta[THb]). Interestingly, the drop in Cox at the end of the trial coincided with a final end spurt in treadmill speed and concomitant increase in skeletal muscle recruitment (as revealed by higher lower limb EMG).
Results confirm the large tolerance for change in Cox during exercise at sea level, yet further indicate that, in conditions of self-selected work rate, cerebral deoxygenation remains within a range that does not hinder strenuous exercise performance.
在恒功和递增至力竭测试中，脑氧合（Cox）的减少与运动停止有关。然而，在这种性质的运动中，由于工作率完全或部分由方案决定，因此生态有效性受到限制，并且不知道在自我调节运动期间是否也会发生脑去氧合。在这里，我们研究了在训练有素的跑步者进行 5 公里跑步计时赛期间的脑血液动力学。
每 0.5 公里记录一次感知用力（RPE）和下肢肌肉的表面肌电图（EMG）。通过近红外光谱监测 Cox（前额叶）的变化，通过氧合和脱氧血红蛋白的浓度变化监测 Cox（prefrontal lobe）的变化（Delta[O(2)Hb]，Delta[HHb]）。计算总血红蛋白的变化（Delta[THb] = Delta[O(2)Hb] + Delta[HHb]），并用作区域血液体积变化的指标。
在试验过程中，RPE 从 6.6 +/- 0.6 增加到 19.1 +/- 0.7，表明最大用力。Cox 从基线到 2.5 公里上升（向上箭头Delta[O(2)Hb]，向上箭头Delta[HHb]，向上箭头Delta[THb]），在 2.5 和 4.5 公里之间保持不变，从 4.5 公里下降到 5 公里（向下箭头Delta[O(2)Hb]，向上箭头Delta[HHb]，<-->Delta[THb]）。有趣的是，试验结束时 Cox 的下降与跑步机速度的最后冲刺和骨骼肌募集的同时增加（如较低的下肢 EMG 所揭示的那样）相吻合。
结果证实了在海平面运动时 Cox 变化的较大耐受性，但进一步表明，在自我选择的工作率条件下，脑去氧合仍在不会阻碍剧烈运动表现的范围内。
