Interval Training: Knowing When Enough is Enough



It is crucially important for an athlete to know when enough is enough. And that holds true whether you’re talking about completing one more interval in today’s workout, or deciding whether you need an extra day of recovery after a hard workout or race. I wrote about this in “The Time-Crunched Cyclist “, and I think the following excerpt serves as a good reminder:

When to Stop an Interval Session

Interval workouts are only effective when you can maintain an intensity level high enough to address the goal of the session. A good example is a PI workout. To be effective, these intervals have to be maximum-intensity, high-power efforts. Ideally, the recovery periods between intervals give you the ability to complete all the efforts at consistent power outputs. However, because they are so strenuous, you’re going to fatigue, and you’ll be fighting harder to reach that high power output during the final set. The big question is, as your power outputs start dropping, how do you tell if you should continue with the next interval or shut down and go home?

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I’ve seen a few methods that attempt to quantify the drop in power output over a series of intervals to provide a clear point at which further intervals are not recommended. One of the better ones is provided by Hunter Allen and Andrew Coggan in Training and Racing with a Power Meter. They recommend using the third interval of a VO2max-interval workout as your benchmark. They recommend stopping if your power output in subsequent intervals drops to more than 15 percent below that level. I think that method works best when you’re doing one long string of VO2max intervals, which I prescribe for some advanced athletes, but for most athletes I prefer to break VO2max intervals (PowerIntervals if you’re familiar with CTS workouts) into smaller sets. For example, a PI session could consist of three sets of three PIs with a 1:1 work/recovery ratio during the set and 5 to 8 minutes of easy spinning recovery between sets. Breaking the session into sets typically allows athletes to accumulate more total work at high power outputs.

Breaking PI workouts into sets, however, makes it more difficult to provide a clear-cut stopping point based on fatigue. For example, it’s entirely possible that the third interval of your second set could be 15 percent or more below your power output from the intervals in your first set or even the beginning of the second. But with 5 to 8 minutes of easy spinning recovery before you begin the third set, you may very well recover enough to match or even exceed your performance earlier in the workout.

Rather than automatically cutting your workout short if your power outputs are starting to fade, I recommend first adding some time to the recovery period between intervals. This means that if your power output from one PI to the next falls by 15 percent or more, add 1 minute to the recovery period immediately following that effort. If the next interval is no better than the one before it – despite the extra recovery time – then you’re done for the day. Don’t add more than 1 additional minute of easy spinning between efforts, and don’t change the recovery periods between sets. If the added recovery time allows you to get through the end of the workout – or even just a few intervals closer to the end – that’s great. Completing the work will help you perform your next PI workout without having to add recovery time.

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When it comes to SteadyState and OverUnder Intervals, which target improvements in power at lactate threshold, it’s not uncommon for athletes to struggle in the final 2 to 3 minutes of an individual interval. After all, these efforts are 8 to 12 minutes long, and they are not that far below the workload from a CTS Field Test (2 x 8minute time trials). However, struggling in the final 2 to 3 minutes of an SS or OU Interval is not cause to skip the next effort. More than likely, following several minutes of easy spinning recovery, you’ll be able to repeat or exceed your performance in the previous effort. You’ll know it’s time to stop if you can’t reach the prescribed training intensity within the first 60 seconds of an interval, or if the perceived effort to stay at that power output makes the interval feel like an all-out, do-or-die time trial. SteadyState Intervals should feel like 7 on a 1 to 10 scale of perceived exertion, with ClimbingRepeats at 8 and OverUnders at 8 or 9. Only PIs should feel like 10, and if you’re not going anywhere, on top of feeling like your eyes are going to pop out of your head, then you’re done for the day.

When to Skip an Interval Workout

I can’t tell you the number of times I’ve rolled away from the CTS office in Colorado Springs completely convinced I was too tired to have a good workout, only to return 90 minutes later after hitting every single power output I was shooting for during my intervals. The trick is understanding whether you need a kick in the butt to get you out the door or an extra day of rest so you can get back to kicking butt on the bike.

Since time-crunched athletes have so little time each week to ride anyway, your decision shouldn’t be whether or not to ride, but rather whether or not you should complete the scheduled interval workout. You should get on your bike regardless, if for no other reason than to ensure that your already limited training time isn’t siphoned away any further.

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If you’re feeling tired when you get on your bike, it’s a good idea to start with a focused warm-up and see if that kick-starts your motivation and energy systems. After 5 to 10 minutes of moderate-paced riding, complete the following:

1 minute FastPedal
1 minute easy recovery
1 minute FastPedal
1 minute easy recovery
1 minute PowerInterval

By this point you should be about 15 minutes into your ride, and you have completed a few efforts. That should give you enough real information to evaluate whether you’re ready to have a high-quality interval session. If you felt like you were really dragging in the PI, or your power output for the effort was considerably lower than normal for a 1-minute effort, I recommend skipping the scheduled interval session and instead completing a moderate-paced endurance ride. If you were merely struggling with motivation to get out the door, your body will respond positively to these short efforts, and they will effectively “blow the crap out of the carburetor”. But if your body doesn’t come around after these short “openers,” you’re most likely too fatigued to have a high-quality interval session today.

And one last note about recovery: when in doubt, err on the side of more recovery. Take the extra day off or the extra day of recovery spinning. You get more benefit from a great workout than you do from a week’s worth of mediocre ones.

Chris Carmichael
CEO/Head Coach
Carmichael Training Systems

4 Responses to “Interval Training: Knowing When Enough is Enough”

  1. David Neale on

    I am 63 years old, used to be very fit and i have taken up cycling about a year ago. I seem to have hit a plateau having lost about 6kgs and improved my cycling so I can ride 2 or 3 30km rides each week with a longer ride on Sunday, (50+kms). But I often feel fatigued either during the longer ride or between rides. I don’t have a power meter and, to be honest, I can’t afford one but i do have a CyclePro indoor trainer that my wife treated me to! I want to break through to the next level but seem to be getting nowhere fast….

    • Geoffrey on

      For me, breaking through to the next level has always required substantial variation in riding intensity during the week. For example, tues sprints, thur paceline or short intervals, sat or sun long ride at slow speed or mixed mountains and slow speeds, and brief easy pace rides the rest of the days. Sprints are full speed absolute maximum gonzo fast but just for 10-20 seconds, with rest of 5 min between. Do about 4 to start then add one more each week. Similar progression is good in the other high intensity days.


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