Three Ways of Knowing How Hard to Go During Intervals

Talk Tests, RPE, “Fast and Fastest”

I’ve been writing a lot of training plans for runners and triathletes lately. 

And honestly, setting up intensities gets confusing as hell. 

Intensity is how hard you go during the particular workout. 

With most training plans I create, you’ll do two workouts a week that are hard.

But how hard?

How do you know how hard to run or ride?

Here are three ways of knowing how hard to go during interval sessions while running, cycling, or swimming that don't require a device or complex workout plan.


If we understand how our bodies utilize energy, it helps us understand how best to target our training. 

Think of the energy systems as a rocket bound for Mars. 

The first section (ATP-CP) gets the rocket off the ground quickly and forcefully but lasts only a few seconds. The second stage (anaerobic) provides a slightly longer boost to get into space, and the third (aerobic) keeps the space capsule going to where it’s going. 

So our bodies have three distinct energy systems, yet all three work as a continuum, providing different amounts and sources of energy depending on the activity. 

The only problem with the rocket analogy is that you use some of all systems while doing your endurance sport. 

Get After It

When we do intervals, we often don’t go hard enough. 

Intervals are tough. 

They are not for the faint of heart.

But they work. 

They boost heart rate function, buffering capacity, and the ability to more efficiently utilize oxygen, fat, and glucose as fuel sources. 

Intervals increase endurance, strength, and speed. 

What’s not to like. 

Besides, of course, doing them…

Which suck. 

Devices Can Help

I’ve programmed several workouts into my Garmin, so when I’m doing intervals, I can see exactly how hard to go when I’m using a bike with a power meter. 

I also do these on my trainer so I don’t have to worry about seeing where I’m going! 

You can also program Garmin devices and other devices to have beeps when you’re in the right heart rate zone.

But your heart rate lags when you’re doing short intervals.

You don’t often get into the right training zone until up to a minute into the intervals, and these hard intervals are often only 30 to 90 seconds long! 

Pace is Another Metric

Runners and swimmers can use pace or a percentage of threshold pace, and a good device can help pinpoint your pace. 

But you still have to keep looking at your watch to know exactly what your pace is. 

While there are pace guides available (I have one to set up plans for runners), it is honestly really difficult for me to know how fast to go. 

Three Alternative Ways to Monitor Your Intensity

Here are three non-device ways of knowing how hard to go during intervals.

Talk Test

You can measure intensity by how well you are able to talk or sing.

The Talk Test has a surprisingly good correlation to heart rate and VO2.

Here are your zones with corresponding zones in a five-zone model

Recovery (zone 1): You are able to have a normal conversation.

Endurance (zone 2): You are able to have a normal conversation, but you can’t fully discuss religion or politics because you can’t get enough air for that. You can sing but not the full chorus of Handel’s Hallelujah! 

Tempo (zone 3): You can have a conversation but not speak in full sentences. You won’t be able to sing much. And I, who can’t stay on key, lose all ability to sing a melody.

Threshold (zone 4): You can talk, but don’t want to. No singing. None. 

VO2 Max (zone 5): You can say individual words but only in an emergency, like “help.” You are, however, able to curse your coach in colorful language. 

Rate of Perceived Exertion or RPE

Basically, you know how hard to go during intervals on a one to 10 scale effort scale.

One is getting off the couch to get another cup of coffee. 

Ten is a “I think I’m going to die” effort. 

Typically an endurance ride is about a five. Hard, but you can go all day.

Tempo is a 6; threshold is a 7 or 8; and VO2 max is 9. 

The challenge with RPE, though, is that how you feel is entirely subjective. 

If you aren’t used to pushing yourself, for example, a seven might feel like a 10. 

How Hard to Go? Fast or Fastest!

You have two speeds to do most shorter intervals: fast and fastest.

Fast days are for threshold level work; fastest days are for VO2 efforts, depending on which system you’re targeting in training. 

What’s key is that you keep the same intensity for the whole time. 

The end of the interval will feel really really challenging to keep up the intensity. 

So you run fast for the whole 60 seconds and keep at the same intensity. 

Or, for a VO2 max effort, you would run faster. 

You should try for the same pace, but as you get more tired, the same pace will increase the intensity.

Systems Determine How Hard You Should Go

Your tempo intervals should be hard.

Your threshold intervals should be harder.

Your VO2 max intervals should suck. They just do. 

But, like I said earlier, the value of threshold and VO2 max efforts far exceed the temporary discomfort. 

It’s tough to know how hard to go during intervals.

I usually tell clients to try the Talk Test first. 

Or, for people who are working on straight speed, find a park or beach or open stretch to run that will take you 30 to 90 seconds. 

Or go to a track. 

Here are three ways of knowing how hard to go during interval sessions while running, cycling, or swimming that don't require a device or complex workout plan.
Photo by Andrea Piacquadio from Pexels

That’s your interval. 

Keep trying to beat your time. 

Knowing how hard to run or ride during an interval session is always a tough one, especially for runners. 

Using the Talk Test or the Fast or Fastest method can help you estimate your intensity to get the most out of your session. 

It’s tough to navigate all of the intervals, strength training, and endurance work. 

Hop on a Virtual Coffee call with me. 

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