Interval Training, Power and Heart Rate

Monday, October 12, 2015 by Coach Tommy

Suppose I gave you this bike workout:

Warm up for about 20 minutes. Then do 30 x 30 seconds at z5 (VO2Max) with 30 seconds z2 (Steady State) between each interval. Cool down the last 10 minutes.

How would you gauge your intensity for these 30 second intervals?  This is an important question.  Do them too hard then you’ll struggle to get in all 30.  Or do them too easy then you don’t accomplish the purpose of the workout.

If you try to use heart rate for short intervals, you will most likely try way too hard to get your heart rate into your VO2Max heart rate zone within the 30 second interval.  Below is a chart of a workout like this.  The red curve is heart rate.  The dashed line is Threshold Heart Rate.  The red bar is this athlete’s VO2Max heart rate zone.  The saw tooth nature of the heart rate curve is the individual 30 second intervals.  The athlete never got his heart rate into his VO2Max heart rate zone, but that’s OK because he has a power meter on his bike.

(Click the picture to enlarge)


The chart below is the same workout.  This chart displays the athlete’s bike power data.  The purple curve is power.  The dashed line is Functional Threshold Power.  The purple bar is the athlete’s z5 VO2Max power zone.  Looking at the power data, it’s obvious the athlete achieved the purpose of the workout – 30 x 30” in VO2 Max power zone.  Perhaps the athlete actually went a little too hard; the tops of the power curve are peaking out of the VO2Max zone, but overall I call this a successful workout.


Below are both sets of data – Heart Rate and Power – displayed on the same chart.  Now, it’s really obvious what’s happening.  The intervals are just too short for the athlete’s heart rate to catch up to the true intensity of the intervals.  This is one reason power data is so superior to heart rate data.


So, should we only use power on the bike?  No.  Notice the heart rate data at the end of the interval session.  His heart rate climbs up and stays up for the last 4 intervals.  This tells me that he was becoming fatigued from the previous 26 x 30 second VO2 Max intervals.  And notice the power on the last interval is a bit lower than the rest.  This tells me 30 x 30 VO2 Max was just enough to accomplish the purpose of the workout.

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