How to Measure Training Intensity: Relation Between Heart Rate and Training
Sports performance, improving general fitness, weight control, or developing surf-specific fitness. If you have one of these goals, it is important to monitor your Heart Rate during training. 
Heart Rate (HR) control and monitoring is an excellent tool, to manage training intensity intervals more precisely.
Even without a heart rate monitor, it is relatively easy to do this same monitoring, although less accurately. To do this monitoring you can use the Borg Scale.
What is the Borg Scale?
The Borg Scale, or Borg Table, from Swedish physiologist Gunnar Borg, is a list of sensations, which allow the subjective classification of an individual’s effort.
Subjective Perception of Effort (PSE) is a valid method in monitoring intensity in cardiovascular training.
The reliability of intensity ratings in strength training has a margin of error. However, it is a good tool.
How it can help you?
By using the chart, you can also transfer the sensations you have during your surfing sessions. Then try to characterize your effort, for example when you paddle out to the peak, when you finish riding the wave, or when you paddle out more vigorously to catch the wave.
If you identify the sensations, you will be able to understand what kind of intensity you are using. By understanding the intensity areas, you’ll have information about what intensities you can train on land, when you can’t do it in the sea.
Whether you have a heart rate monitor or not, you can now train more assertively.
For more information, please also check this article where you will find another tool to measure your training HR.
Fill in your data: Age and Resting Heart Rate and the tool will automatically give you your training Heart Rates for different intensity intervals. Depending on your goals, you can now monitor your HR training interval. 
