Effects of physical training and detraining on sympathetic neural regulation of cardiovascular system

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It is well known that physical training improves cardiovascular regulation but it is not clear how long the improved regulation persists after exercise training. This project attempted to investigate the adaptive change in sympathetic nervous activity (MSNA), which plays an important role in the control of cardiovascular regulation during exercise, to exercise training and detraining. Healthy volunteers performed high intensity handgrip exercise training for four weeks. MSNA was recorded from the tibial nerve by a microneurography technique during fatiguing static handgrip exercise and following post-exercise forearm occlusion (PEFO).Findings :1. MSNA increased in relation to the duration of handgrip exercise time and reached its maximal level at the onset of fatigue. During PEFO the MSNA response was greater than observed in the resting, pre-exercise control level.2. The MSNA response at the onset of fatigue was increased post-training compared to pre-training, while the MSNA response to PEFO was unchanged post-training.3. After four weeks detraining, the MSNA response at the onset of fatigue decreased compared to the immediate post-training and responses and the magnitude of the detraining responses remained unchanged for up to one year The MSNA response to PEFO was unchanged by training. In conclusion, although central command and muscle reflex are factors that can enhance MSNA during muscle contraction, the muscle metaboreflex-induced increase in the MSNA response to PEFO was not modulated by resistance training. On the other hand, resistance training increased central command and this effect enhanced the MSNA response transiently.