Rate-limiting factors of oxygen uptake kinetics during exercise

与传统的周期测量法（CE）相比，膝关节伸肌（KE）运动模型产生了不同的肌肉和纤维招募模式、血流量和能量反应。本研究验证了以下假设：1)同一受试者的直立两腿KE和CE会产生根本不同的肺摄氧量（pVo_2）动力学（H_1）； 2) KE的肺和肌肉Vo_2 （mVo_2）动力学会有机械联系（因此相似）（H_2）。6名受试者进行了从无负荷到中度（<通气阈值，VT）和重度（>VT）运动的KE和CE转换。除了在CE和KE期间的pVo_2，同时使用脉冲和回波多普勒方法，结合股静脉采血，量化了KE发病时股动脉血流（LBF）和mVo_2的精确时间分布。H_1: KE （~ 12ml/W/min）与CE（~ 10）相比，中度和重度运动时pVo_2快速分量的增益（振幅/工作速率）均较高，但快速分量的时间常数无显著差异。此外，重度KE的平均反应时间（MRT）和慢速部分对总体反应的贡献显著大于CE。H_2: mVo_2组分的时间常数。此外，重质KE中pVo_2的缓慢组分明显，反映了mVo_2的逐渐增加。KE发生后LBF初始动力学显著快于pVo_2第二阶段动力学（中度：时间常数LBF = 8.0 ^^+__- 3.5s, pVo_2 = 32.7 ^^+__- 5.6 s， P<0.05；重度：LBF = 9.7 ^^+__- 2.0 s, pVo_2 = 29.9 ^^+__- 7.9 s， P<0.05）。LBF的MRT也明显快于pVo_2。这些数据表明KE与CE的pVo_2动力学时间常数相似，但增益更大。此外，对于KE，在KE期间肌肉血流的时间分布和pVo_2之间存在显著的分离。

The knee extensor (KE) exercise model engenders different muscle and fiber recruitment patterns, blood flow and energetic responses compared with conventional cycle ergometry (CE). This investigation tested the hypotheses that: 1) upright two-leg KE and CE in the same subjects would yield fundamentally different pulmonary oxygen uptake (pVo_2) dynamics (H_1), and 2) pulmonary and muscle Vo_2 (mVo_2) kinetics for KE would be mechanistically linked (and therefore similar)(H_2). Six subjects performed KE and CE transitions from unloaded to moderate (<ventilatory threshold, VT) and heavy (>VT) exercise. In addition to pVo_2 during CE and KE, simultaneous pulsed and echo Doppler methods, combined with blood sampling from the femoral vein, were utilized to quantify the precise temporal profiles of femoral artery blood flow (LBF) and mVo_2 at the onset of KE. H_1: The gain (amplitude/work rate) of the fast component of pVo_2 for both moderate and heavy exercise was higher during KE (〜12ml/W/min) compared with CE (〜10), but the time constants for the fast component did not differ. Further, the mean response time (MRT) and the contribution of the slow component to the overall response for heavy KE were significantly greater than for CE. H_2: The time constant for the component of mVo_2. Moreover, the slow component of pVo_2 evident for the heavy KE reflected the gradual increase in mVo_2. The initial LBF kinetics following onset of KE were significantly faster than the phase 2 pVo_2 kinetics (moderate: time constant LBF = 8.0 ^^+__- 3.5s, pVo_2 = 32.7 ^^+__- 5.6 s, P<0.05; heavy: LBF = 9.7 ^^+__- 2.0 s, pVo_2 = 29.9 ^^+__- 7.9 s, P<0.05). The MRT of LBF was also significantly faster than that of pVo_2. These data demonstrate similar time constants but a greater gain for pVo_2 dynamics of KE vs. CE. In addition, for KE there was a striking dissociation between the temporal profiles of muscle blood flow and pVo_2 during KE.