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Plasma norepinephrine response to exercise before and after training in humans
Summary
Endurance training reduces sympathetic nervous system activity during submaximal exercise. While resting plasma norepinephrine levels remain unchanged, trained individuals show a lower norepinephrine response to absolute workloads, indicating improved efficiency.
Area of Science:
- Exercise Physiology
- Cardiovascular Regulation
- Autonomic Nervous System
Background:
- Sympathetic nervous system activity, measured by plasma norepinephrine (NE), is a key indicator of physiological stress.
- Exercise training is known to induce adaptations in cardiovascular and autonomic functions.
- Understanding how training affects sympathetic response to different exercise intensities is crucial for optimizing training protocols.
Purpose of the Study:
- To investigate the effects of a 20-week endurance training program on plasma norepinephrine levels at rest and during exercise.
- To determine if exercise training alters sympathetic nervous system response to absolute and relative exercise workloads.
Main Methods:
- Ten healthy male subjects underwent a 20-week bicycle ergometer training program.
- Plasma NE concentrations were measured using a radioenzymatic assay at rest and during exercise (absolute and relative workloads) before and after training.
- Maximal oxygen uptake was assessed to confirm training adaptation.
Main Results:
- Maximal oxygen uptake significantly increased post-training, confirming successful adaptation.
- Resting plasma NE levels did not change significantly after the training program.
- During absolute workloads, plasma NE concentration was significantly lower after training, indicating reduced sympathetic response.
- At equivalent relative workloads (heart rate matched), plasma NE levels remained unchanged, suggesting preserved sympathetic drive relative to perceived exertion.
Conclusions:
- Endurance training leads to a more efficient sympathetic nervous system response during submaximal exercise, particularly at absolute workloads.
- Sympathetic nervous activity, as reflected by plasma NE, appears to be maintained in relation to relative exercise intensity (perceived exertion) post-training.
- These findings highlight the differential impact of training on absolute versus relative exercise intensity responses of the sympathetic nervous system.