Ask The Expert: When Does an Interval Really Start?

The question of when a interval effort really starts has been posed a number of times. Short intervals of less than a minute leave little room for question. However, the confusion often surrounds the longer 3- to 10-minute threshold intervals. With a threshold interval, the goal is to sustain a heart rate between 97% and 103% of threshold (VT2, LT2, LTHR) or FTP (functional threshold power) for the entire duration. The question lies in the amount of time it takes to arrive at threshold, or what I like to call “cruising altitude.” Depending on a rider’s fitness, fatigue, and a whole host of factors, arriving at threshold will vary from one person to another. Does the amount of time it takes for a rider to get to threshold affect when the interval effectively starts?

It Starts at Go


  1. Chuck,

    Do you have specific profiles that you are eluding to in this commentary. I am having a hard time bridging the gap of providing my students that are in class fore more than the above mentioned HIIT workout every class.


  2. Bonnie,

    You are welcome… We are in a tough business that requires us to explain complex physiological responses to regimented stressors. Without the aid of tools like heart rate monitors, power meters and structured metabolic testing equipment, what we say is often a shot in the dark.

    Moreover, it seems, a large chasm exists between the kind of training we could provide and what most of the our riders really come to class for.

    Some groups will eat it up and ask you provide more. This particular profile of classes that Tom is suggesting is among the best for riders from that group. This is the sort of class that will attract outdoor riders if that is of any appeal to you. They can appreciate – or at least learn from it. In such classes, you are coach, not class leader. You will spend most of your time off the bike. The group must get its motivation mostly from your coaching rather than the music.

    Most all other groups will prefer the more common ‘Spinning®’ class where you lead the class though a combination of efforts to great motivating tracks. Everyone’s heart rate goes up as far as they let it. There is some sweat and everyone leaves feeling that they got their workout.

    In both cases you have satisfied customers. And that is really, the bottom line.

  3. Bonnie,

    I’m sure Tom and Jennifer will have a more scientific answer but I’d like offer up my explanation of what a five minute threshold effort feels like.

    First the essence of this post is really – IMHO – about your riders learning to feel what such threshold efforts feel like by experimenting with shorter to longer intervals. Like Tom said, the shorter intervals more or less take care of themselves… Hit it hard it will all be over before you know it.

    For the longer efforts, frankly, there is no perfect answer. Without heart rate monitors, power meters and clocks (as in our cycle studios) It is hard to nail down. Until and unless your riders undergo field testing or metabolic testing the only way they’re going to know what a five minute threshold interval feels like is from experience.

    Truth be told, without said metabolic testing, one must go over threshold to know where it is. And that is how I explain it. (I have the same low percentage of heart rate monitor users.) How do they know they’re past threshold? When they’re feeling an overwhelming urge to slow down. At that point tell the riders it is ok back off a bit and see what happens. As they recover, that feeling of needing slow down, will diminish and perhaps the effort will start to feel – for lack of a better term – too easy. That is the point where they need to ramp up the intensity again.

    Like a dampened sine wave (think of my example of the new pilot trying hold their airplane on one altitude) the amplitude of the wave will get smaller and smaller until the rider just knows.

    Of course the longer the effort the more difficult it will be to sustain high intensities. But by the time your riders are there, you can start aerobic capacity training.

    1. Chuck – just checked back in and saw this. I appreciate such a detailed and thoughtful response. Very helpful – thank you.

  4. Using your example of Mary, what would be really helpful to me would be to have some cues on what a 5-minute threshold interval should feel like. Our bikes have a resistance knob, and that’s it – nothing showing power, time, cadence, etc. And, despite my often talking about the benefits of a heart rate monitor, which at least provides some information on how hard they are working, maybe only 2 out of my class of 15-20 have one. I try to often focus on what various intervals should feel like in terms of breathing, etc., and let them know song bpm and subsequent rpm so they have an idea of their cadences, but addition cues/descriptions on what that feel like would be a big help for me.

  5. Tom,

    Great post… This is the perfect class profile for breaking through what I cardio wariness. Many of our riders are wary of explosive or extended high intensity efforts because they’re not used to the feeling of a sudden rise in heart rate.

    With this profile they can experiment not only with how their body reacts to a timed sustained threshold effort but also break through the cardio wariness of what happens when they do.

    I like to explain that until and unless one has done this many times with heart rate and power, this exercise is like a student pilot learning to hold altitude. At first they way over shoot and then over correct. But with time they learn how to taper the climb to hold at a steady altitude. Same with threshold intervals

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