Advice on dealing with high heart rate in a given workout

As your structured training load increases due to an increase in intensity, duration, frequency , or all three, your body learns to adapt and become more fit.  Muscles become stronger, the heart pumps more blood per stroke, blood chemistry changes, and a general adaptive process attempts to accommodate the new stresses placed upon it.


During the course of a season of training, we may push our bodies too far and essentially "paint ourselves into a corner" with regard to recovery.  Usually, we notice that we are reaching too far with regard to our new workload and ironically, this is known as "overreaching".  It usually takes the athlete 2-3 weeks to recover from the fatigue and poor performance that is usually associated with overreaching.


Overtraining can best be defined as "chronic overreaching".  Very few athletes actually become overtrained since most will back off their training load when they notice a decrease in their performance.  An actual episode of overtraining can take 2-3 months to fully recover.


One of the symptoms of overreaching is an elevated heart rate at a given effort (i.e. pace or power output).  If the athlete notices these symptoms during training, it is usually best to cut the workout short and begin a period of reduced training stress.  


Joel Friel (author of Cyclists and Triathletes Training Bible) had a recent discussion with John Post M.D., and they published his recommendations on his blog.  Here is an excerpt from a recent post:

"However, if the high exercising heart rate is unusual for you then you may indeed have a problem. But let’s further define “high” here. There are going to be days when your heart rate rises above what you normally see by perhaps 10 bpm or slightly more just because of fatigue, overreaching, overtraining, too much caffeine or similar product, or a hot day. This is not unusual at all. You may need to back off and slow down or even abandon the workout that day. This happens to everyone from time to time.

But if your heart rate is well above 10bpm over what you normally see at a given power, pace or perceived exertion (which may not work in this case) then you could have a health problem. But first check to make sure your heart rate monitor is working correctly and there are no errant signals.

Such an unusually high heart rate happened to me in 1994 while running a half marathon. Of course, as the dummy I am, I finished the race, albeit at a slower pace. After weeks of testing my doctor finally determined it was a case of viral myocarditis. That cost me seven months of training.

Another condition to be aware of is atrial fibrillation (“a-fib”). I won’t go into detail on this as you can read more about this here on Dr. Post’s blog. 

So if you mean a “high” heart rate as one high relative to what you normally see at an otherwise common intensity and you’ve ruled out the heart rate monitor as the source of the “problem,” then see your doctor."

We need to look at a trend when viewing heart rate, so an isolated incident with elevated measurements may not indicate a problem.  Heart rate can slowly drift upwards at a given pace or power as an athlete becomes dehydrated or fatigued.  This phenomena is called "CV Drift" or "Cardiovascular Drift".

As the athlete warms up and begins to sweat, blood is brought very close to the surface of the skin in order to increase cooling and the volume of the blood being pumped to muscles and organs decreases.  This decrease in blood plasma volume causes a reduction in arterial blood pressure and heart stroke rate volume.  In order to combat this drop in blood pressure, the heart rate must elevate in order to pump the "thinner" blood to the body.  

CV drift is largely controlled through proper hydration and heat acclimation, and an elevated heart rate for a given pace or power can best be controlled through proper rest and recovery.  If the condition becomes chronic, it is recommended that the athlete seek medical advice.

The build phase of endurance training is marked by increases in steady-state aerobic exercise, and provide an excellent opportunity to monitor changes in heart rate during prolonged exercise.  For example, after monitoring your heart rate at Zone 2 or Marathon pace for several weeks, you will become familiar with a normal range.  If the numbers fall out of this range, your coach can help you find out why this might be happening.

Per the recommendations by John Post M.D., we suggest that if your heart rate is well above 10 BPM for a given pace or power zone, that you consider factors such as your hydration level, potential for overreaching, etc. and contact your coach to find a solution.