How the heart betrays stress

June 30 2015

The fitness industry is abuzz with the discovery that your heartbeat can be analysed to measure exactly how stressed you are.

Heart rate. It’s that staple of training, where you work out your maximum heart rate and then use a heart rate monitor to tell how hard you’re working, since your heart provides a more objective gauge of how hard you’re working than your head does.

But it seems your heart rate can tell you more. A lot more. Fitness science is only just waking up to it. The “variability” of your heartbeat — the difference in length of time between each heartbeat — is turning out to be a perfect indicator of how stressed your system really is, and whether you’re really able to work harder regardless of your actual heart rate.

One of the people excited about this insight is Rodney Corn, who has a Master’s degree in biomechanics from California State University and is the co-founder of Personal Training Academy Global (PTA Global), which trains personal trainers around the world.

He told Fitness First that heart rate variability is a direct, objective window into your body’s stress levels, and tells you whether or not you can actually handle more exercise. In scientific terms, it’s a window into your autonomic nervous system “which reveals what your body’s capable of doing from a stress standpoint,” says Corn.

A quick explanation of the autonomic nervous system reveals why: the role of this system in your body is to regulate involuntary body functions, such as heartbeat, blood flow, breathing and digestion. But it’s actually a balancing act between its two subsystems, the sympathetic nervous system (which is in charge of your fight or flight response and raises your heart rate in response to exercise or stress) and the parasympathetic nervous system (which tries to conserve resources and brings down your heart rate).

“When someone is at rest, when they’re at home, there should be significant variability between heartbeats, meaning that it shouldn’t be a consistent distance or time between them,” says Corn. “That indicates that the system is ready to adapt at any minute. It can go in almost any direction, meaning I can go wherever you take me because I don’t have a consistent rhythm.

[caption id="attachment_126" align="alignright" width="300"]Rodney Corn2 Rodney Corn[/caption]

“Now, as we start exercising, which is a stress, our heart rate starts to go up into the higher heart rate zones, and those beats will start to get much more symmetrical. So now we’re getting a much more unified beat, or distance between them. That’s a natural thing, then you come back down and you go back to your relaxed state, and you go back to the variability.

“But what happens when people get stressed, or when they get in a high stress situation, even though they’re at rest and their heart rate may be 60 beats per minute, the heartbeat remains consistent rather than variable.”

Corn says this means the sympathetic nervous system is in overdrive and the parasympathetic nervous system can’t overcome it and bring your system back down to recover. “It can’t get back to where it wants to be because the system is driving itself too hard: it’s stuck in overdrive. You know, the gas pedal’s stuck and it’s irrespective of the heart rate per minute.”

The application for this knowledge, says Corn, is that “it can now tell me how stressed my system is. When I know how stressed my system is, then it will help me — whether I have an app that tells me or whether I have a trainer who understands it — how I should be modifying my training session each time I train so I’m not overstressing my system, so I’m staying within the boundaries to make sure that I don’t create too much stress.”

"Heart rate variability is a direct, objective window into your body’s stress levels."