Autonomic Nervous System Adaptations
The autonomic nervous system, which controls involuntary functions like heart rate, also adapts to regular physical training. It consists of two main branches: the sympathetic nervous system, often called the “fight or flight” system, and the parasympathetic nervous system, known as the “rest and digest" system.
Sympathetic v Parasympathetic
When you exercise, the sympathetic nervous system kicks in, increasing your heart rate to pump more blood (and therefore more oxygen and nutrients) to your muscles that are working hard. On the flip side, the parasympathetic nervous system is more active when you are at rest, helping to lower heart rate and promote recovery.
Vagal tone refers to the activity level of the vagus nerve, which is a key player in controlling your heart rate. Think of it as the "calm-down" signal for your heart. When the vagus nerve is more active, it helps slow down your heart rate.
For athletes and regular exercisers, improved vagal tone is a good thing. It means that your heart is better at switching gears—from being pumped up during exercise to calming down afterward. This is a sign that your body is adapting well to the physical stress of your workouts.
Vagal tone is closely related to another term you might have heard: heart rate variability (HRV). A higher HRV is a sign that your heart is more flexible in responding to changes, whether it's the stress of a workout or just the ups and downs of everyday life. And a more flexible heart is a healthier heart, which often comes with a lower resting heart rate. Most sports watches have functions to measure your heart rate, although some are more accurate than others. There are also apps such as Elite HRV that you can download on your phone.