Having written a number of pieces on heart rate monitors and heart rate monitored training, and having used one in my training for over 10 years, you can surely see I am completely behind the heart rate monitor.

As a training tool, it is one of the easiest and most used ways to monitor training intensity during workouts. It is also it is an affordable way for any athlete to track their physiological and health status.

But as with all good things, there are a few "downsides" to training with a monitor which need to be kept in mind.

Day to Day variability: As you have surely noticed, your heart rate differs from one day to the next, and has been shown to vary between 2 and 6 b/min.

It is therefore recommended that you use training zones that take this variation into account, and have a range of between 15-20 b/min.

Body position during activity: If you are a Triathlete, your training will put you into 3 basic positions:
  • Supported - Swimming
  • Semi-supported - Cycling
  • Unsupported - Running
Being in an Unsupported position, requires more muscles to be active, and thus will illicit higher training heart rates.

This is why it is important to set up your training zones for all 3 disciplines.

Temperature: I am sure we have all experienced this one.

Cycling in hot conditions will lead to an elevated heart rate, to deal with the Heat stress imposed on the body, and does not accurately reflect training intensity. As core temperature increases, so does heart rate.

Heart rate can increase by up to 30 b/min.

Training in cold conditions may under-estimate the training intensity.

Cardiac Drift: This is another physiological phenomenon that many of you will have experienced in your training.

During continuous, prolonged training at a moderate intensity (below Threshold), an increase of up to 20 b/min can be seen. The Cause: increasing core temperature as a result of increased heat load from muscle activity.

You will see a higher heart rate without an increase in output (Speed, Power).

Dehydration: Your hydration status has a direct impact on your heart rate during activity.

As you sweat, you lose fluids, your bodies way of cooling you down through sweating.

If Fluid out > Fluid in then = Dehydration.

Dehydration = a reduction in blood volume, which results in an increase in Heart rate to meet the bodies demand for blood.

Dr. Asker Jeukendrup sums up this entire post nicely in one table:

James Greenwood is a competitive tri and multisport athlete currently training for Ironman Canada 2009. A level 1 Triathlon Coach, he holds a post graduate degree in Exercise Science, and is a Certified Strength and Conditioning Specialist through the NSCA. James is also currently the resident health and fitness programs expert at MyPypeline.com, and has starred in a number of multisport specific fitness videos.
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