Training with Power or Heart Rate? 

We get this question a lot...

What's the better metric for training on the bike: power or heart rate?

Since power-based training has risen to the status of "must have" for effective training for serious cyclists, the use of heart rate as a training metric has been tossed aside by many. The power meter is a wonderful tool and one we strongly recommend (in fact, all our Personal Coaching clients are required to use power). But, without the simultaneous use of heart rate, you are only seeing half of the story and getting half of the benefits.

So our answer is: BOTH power & heart rate are needed for maximum training effectiveness!

Using one without the other is a mistake. Here's why...

• Power (watts) is the direct measurement of the amount of work that is being done.Many will say, "a watt is a watt, and watts don't lie." This is true, power is an absolute. You either have it or you don't on a given a day. However, the effort required to produce those watts on any given day is affected by many variables, and that is where heart rate (HR) comes in.

• Heart Rate (bpm) is an indirect measurement of your bodies response to the work (power) being done. You might hear people poo-poo.  They'll claim that it's affected by so many outside variables, such as sleep, hydration, elevation, temperature, fatigue and so on that a HR measurement is not useful. But ... why are these effects considered a negative attribute? When in fact, it's these very affects wherein the value of training with HR comes in!

Let's look at this example of a training block using both power & HR...

• Your Vo2 Max training block calls for multiple sessions of 8 x 2:00 at your 16:00 max power (or appx. 110-115% of FTP), with 2:00 recoveries, over a 21 day period. Here's a possible scenario...
  • Session 1: you hit your power numbers and heart rate reaches 169-173 bpm by the end of the intervals 3-8. Good start.
  • Session 2: similar results.
  • Sessions 3: you're having a stressful few days a work, not sleeping well. You're able to hit your power numbers. However, your HR is 172-176 for the last few intervals. This is indicating you are putting out more effort to do the same amount of work. Do this for too long and you risk overdoing it.
  • Session 4: you decide to skip in favor of more recovery and do an easy ride.
  • Session 5: you're back to similar results as 1 & 2.
  • Session 6: you hit your power targets, and notice your HR is only 165-169 bpm for the last few intervals. This indicates you're adapting to the workload (power requirement) and now it's requiring less effort to hit the same power. Improved fitness! You're ready to increase load (as in higher power, more reps, or shorter recoveries).

Now granted, this is a simplistic view of things. Do, however, consider that in this example the power reading remained the same the entire time. Had you not had a HRM you would have missed the higher HRs when stressed and maybe dug a hole of fatigue early on. Or you might have missed the lower HRs at the end that indicate you may be ready for a higher training load. Both pieces of information are super valuable in making adjustments in your training for continued improvement.

Power should be the primary metric for high-intensity training at and above our anaerobic threshold.

You then gauge how your body is responding to the workload by using heart rate as the secondary metric. You should always be looking for improvements in lower HR compared to the same power outputs as a sign of positive adaptation. Use both together to be able to gauge your fitness vs. freshness levels on a day-to-day basis. This will allow you to know when you should back off or ramp up based on your body's response to your training program.

So, yes, there are many variables – like sleep, hydration, elevation, stress, and diet – that can affect HR. But these same variables affect how you are able to train and more importantly absorb, or adapt to, the training that you're doing. If you just stick to hitting the power numbers, how do you know when you're improving and ready for an increased load? Or on the contrary, how do you know when you need to back things off a bit because hitting those numbers is more difficult than it should be due to fatigue or a change in training environment?

Our preferred method of testing for anaerobic power development and setting power training zones is doing a Power Test that requires you to perform test intervals of 1:00, 2:00 and 4:00 in duration for max power. As a result, you identify both your Fatigue Rate and max HR to set your power and heart rate based training zones.

With aerobic training, heart rate becomes primary metric.

When you train to improve the aerobic energy system you're looking for two primary adaptations, one in cardiovascular infrastructure (stronger heart, more blood vessels, more mitochondria, etc.), and the other in energy metabolism of using fat for fuel and sparing glycogen at higher and higher outputs. The aerobic energy system requires longer and lower intensity outputs to train for these adaptations. For this reason, heart rate is often more useful as the primary training metric, with power used as the secondary metric to look for improvement in (increase) over time.

When you go for a longer ride, or even longer intervals, focusing on a specific power number requires too much effort and can be frustrating. Instead, focus on a HR range to target. Training to a specific HR for the longer, lower intensity work is easier to maintain and less affected by the immediate terrain and weather. With aerobic training, you're either targeting a specific duration of riding to achieve your training load (i.e. 4 hours at aerobic HRs, where power isn't very relevant); or you can get more structured with say 4 x 10:00 at Aerobic Threshold (AeT) HR where you target a specific, more narrow HR zone for the intervals. Here you check progress by looking for improvements of average power for that HR zone and or less power-fade or "decoupling" between the HR and power measurements as duration increases.

Our preferred method of testing for aerobic development is doing an Aerobic Threshold (AeT) Test that requires you to perform the test interval to a specific HR, and then reference your power for the test interval as your measure of improvement.

In summary, your training program can be far more effective, informative, and engaging if you use both power and heart rate as metrics to gather data.

• When training the top-end energy systems (i.e. Anaerobic Threshold, Vo2 Max, Anaerobic Power and Peak Power), you use power as the primary metric to target workload and use heart rate as the secondary metric to see your response to that workload. From here you are able to make adjustments on the fly (mid-workout even!) and in your extended planning.
  • You can utilize a Smart Trainer, like the Wahoo Kick'r, for power-based indoor workouts if you can't have a power-meter on your bike(s) for both indoors and outdoors.

• When training your lower-end aerobic energy systems, you'll switch things around to focusing on HR while using power as secondary reference to measure your aerobic progress and stamina.
  • This works well for longer rides outdoors where a HRM is easy to have along for the ride and power isn't a necessity.

Are you looking to train more effectively with both power & HR this off-season?

You can purchase our 24-Week Off-Season Trainer Series from Training Peaks that includes our testing protocol as well as a complete build through each energy system to improve your top-end power and fatigue resistant endurance. Check it out HERE

This blog post was written by Cody Waite, professional endurance athlete, endurance sport coach and founder of Sessions:6 Sport Performance. Looking for help with your endurance sport training? Check out S:6’s Training Plans, Team Programs and  Personal Coaching options created to fit your needs and budget.