The Science Of Endurance Troubles Of The Heart

Most endurance athletes head out the door for their training sessions, hit the start button on their heart rate monitor then hit stop at the end. Beyond uploading their files to Strava to see if they clocked up any new PBs, they do not pay much attention to the numbers on what amounts to an overpriced watch. 

In this article I want to cover a couple of common issues that arise when athletes start paying attention to their heart rate rather just hitting the start and stop button. The first scenario is having a high heart rate when you are just cruising along and secondly is struggling to get your heart rate up no matter how hard you push. But before we get in to things, let's have a quick think about how your heart rate is controlled.

How is the heart controlled?
The heart is controlled by two branches of the autonomic nervous system. The sympathetic nervous system (SNS) and parasympathetic nervous system (PNS). The PNS is the 'rest and digest' input that acts as the hearts hand break slowing it down or speeding it up when it is withdrawn. While the SNS is the 'fight or flight' response that stimulates the heart to increase its output by pumping faster and more forcefully. Now with that quick physiology lesson out of the way let's get into it.

Scenario 1: High heart rate while you are cruising
If you are cruising along and your heart rate is through the roof, it is a good sign that your SNS is pumped up. Whether this is from work, life or training stress the stress hormones and nervous activity are causing your heart rate to be higher than normal for the given work load. If this sounds familiar and you are experiencing it for more than a couple of sessions then it is a good signal that your body requires some additional recovery to allow your SNS to return towards normal.

What should you do?
In this case, shut the session down and get some additional recovery as your body is in a fatigued state, your SNS is significantly elevated and it needs some time to balance out. Often a day or two of recovery is enough for you to bounce back to normal. 

"If you feel you are pushing hard but your heart rate is low, not responding as normal it is an indicator that you need some recovery."

Scenario 2:
Low heart rate and you are not able to raise it into your upper training zones. If you feel you are pushing hard but your heart rate is low, not responding as normal it is an indicator that you need some recovery. This often occurs following high training loads when the heart has been bombarded with a large amount of stress hormones for a number of days or weeks (as outlined in scenario 1) and it has become desensitised to them or your muscular fatigue is limiting your intensity. So no matter how hard you try to push your heart rate will not increase and your legs feel like led.

What should you do?
If you are experiencing this you are in serious need of some recovery. Depending on your level of fatigue you may require a solid week of a lighter training load or some extended complete recovery to allow your body to bounce back to full function. If you continue to push through you can start sliding down the slippery slope of overtraining.

I hope this helps you guide your training when you next look down at your heart rate monitor and see something that does not quite look or feel right.

If you have any questions or topics you would like me to cover in future articles please feel free to contact me.

Get out there and train hard, but most importantly train smart.

Originally published in New Zealand Triathlon & Multisport Issue 106, October 2016.