Estimation of muscle fiber recruitment pattern during physical exercise in inorganic phosphate kinetics by ^<31>P-NMR

使用^&lt；31&gt；P-核磁共振的研究报告说，在高强度运动中，无机磷(PI)分裂成高和低pH峰。然而，目前还不清楚是哪个因素导致了这种分裂。我们假设，肌肉纤维募集模式解释了这种分裂。提高~1t；31&gt；P-核磁共振的拆分时间是阐明PI动力学的关键。我们在^&lt；31&gt；P-核磁共振中调整了脉冲的角度和间隔，以允许5秒的间隔数据采集。为了验证这一假设，我们观察了充足和不足氧气条件下的PI模式，即运动后的主动和被动恢复，以及运动过程中有和没有循环阻塞。高pH值PI在小腿屈膝运动结束后消失。低pH值在主动恢复过程中的下降速度明显快于被动恢复过程。这可能是由于被动恢复时快速抽动肌纤维供氧不足所致。同时测量的近红外光谱数据表明，主动恢复期间存在的血液容量比被动恢复时更多，这表明在主动恢复期间肌肉的氧气补充更多。当运动强度低于非闭塞运动强度时，小腿循环闭塞280 mm Hg时，PI峰分裂。这意味着PI代谢覆盖了因缺氧而造成的能量损失。提示快速的痉挛肌纤维募集导致PI分裂。

The studies using ^<31>P-NMR reported that an inorganic phosphate (Pi) splitted into high and low pH peak during a high intensity exercise. However, it was not clear which factor induces this splitting. We hypothesized that a muscle fiber recruitment pattern explains this splitting. It was essential to improve the resolution time of ^<31>P-NMR to clarify the Pi kinetics. We adjusted the angular and interval of the pulse in ^<31>P-NMR to allow a 5 seconds interval data acquisition. To test the hypothesis, we observed Pi patterns under sufficient and insufficient oxygen conditions, i.e., during active and passive recovery from exercise, and during exercise with and without circulatory occlusion.High pH Pi disappeared just after the end of calf flexion exercise. Low pH Pi during the active recovery decreased significantly faster than during the passive recovery. This would resulted from insufficient oxygen supply to the fast twitch muscle fiber during the passive recovery. Simultaneously measured near infrared spectroscopy data indicated that more existing blood volume during the active recovery than the passive recovery, revealing more oxygen supplement to muscle during active recoverty. Pi peak splitting was observed during circulatory occlusion on leg by 280 mmHg at lower exercise intensity than non occlusion trial. This means that Pi metabolism covers the energy loss resulted from oxygen deficit. It is suggested that fast twitch muscle fiber recruitment causes the Pi splitting.