Pace during L4 Interval Sessions Decreases?

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  • #17661

    During hard uphill interval sessions where I base effort on HR (for instance 5 x 4min at Z4), I notice that the pace I use in the first few is higher than in the last few (maybe 10-11% slower – otherwise my HR spikes above Z4).

    Is this fairly standard and attributable cardiac drift/lactic buildup or indicative of something else that I should be concerned about?

    Does anyone else see this happening?

    I have a fairly strong aerobic base (have been following UA training plans for a few years) but delta between AnT and AeT is closer to 13% than the magic 10%!


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    Anonymous on #17686

    This is common when adding Z4 intervals. The slowing can (probably) be due to local muscular fatigue. I’d suggest the following options as a course of action.

    Shorten the ‘on’ time and try the same total volume so in stead of 5x4min try 7x3min. And/or Take longer recovery intervals. If you are slowing 10% that means that the higher force Fast Twitch fibers are dropping out of the recruitment pool. So they are not getting the desired training effect.

    Another way, and our and Kilian’s preferred method of adding Z4 intervals is with 30-30s. I’ve used them for years with skiers and runners. Sam just wrote an article 30-30s and it should go live on the site in the next week or two.


    yesisaidyes on #17703

    Thanks Scott – this is interesting.

    So to be clear, I can complete the workout in terms of getting to Z4 for the required time – the issue is that in the last few I end up going over and into Z5 (I use the Friel running zones from TP based on my AeT).

    Based on the fact that I can get the work done but just at a higher heart rate makes me think this is more of an aerobic issue than a muscular one. What do you think?

    I am well familiar with 30/30s from Nordic and look forward to Sam’s article! I understand Kilian prefers to do them for 3 hours!


    Anonymous on #17723

    Another possibility is that your initial pace is higher than zone 4.

    If you’re using heart rate to indicate intensity, then I suspect that you may be going too fast in the first interval(s). In my experience, the lag in heart rate makes it almost useless in gauging high intensity.

    In the first interval, and at a constant pace, how many minutes does it take for HR to get to the target range?

    If it gets there quickly, then I suspect your pace is well above the target. If HR doesn’t reach Z4 until the end of a 4-5′ interval, then I suspect that you’re in the right range. In subsequent intervals at the same pace, HR will likely reach the target bpm faster.

    Does that make sense? (Scott J. what are your thoughts on this?)

    Anonymous on #17724

    Ack. My apologies. I should RTFM. I just read that you’re using pace zones as your targets, not HR.


    yesisaidyes on #17725

    @Scott Semple – no, you are right, it is HR zones. By “running” zones – I meant the 7 Friel HR zones for running on Training Peaks (the auto set).

    It’s funny, I usually jack up the pace on the first interval intentionally to get my HR into the zone as quickly as possible during that first interval (I figured that was better???). But yeah, it gets there much more quickly on latter ones.

    So maybe keep the pace at a consistent level to get the HR into the zone by the middle to end of 4 min interval on the first one and see what happens if I keep it there for the rest without creeping in to Z5.

    Super helpful, thanks!

    Anonymous on #17732

    Like Scott Semnple I may not have read your post carefully enough.

    You are using pace but you are doing these on some uphill course right. So you are not really using something like a target pace from a race if I understand correctly. Normally when we refer to using Pace as the measure of interval intensity we do this by taking some recent race or time trial effort to establish the current pace you can race at. Then we’d use that race pace to set the interval pace. For building endurance you’d do longer race pace or slightly slower pace (depending on race length). For improving speed we’d use paces faster than race pace for shorter reps (again the lengths and pace depend on target race distance).

    In mountain sports pace goes out the window so we are stuck using HR as proxy for effort.

    I suspect what you mean when you say that you are using pace is that you are using a set distance on this hill and that to maintain the time you set on reps 1-2-3 for reps 4-5 your HR goes higher than it did on those first 3 reps. Is this correct?

    If it is then you are correct the issue is probably more central Cardiac output related that it is local muscular fatigue.

    I’m not a fan of the Friel zones systems as I understand them. They use arbitrary % of usually Lactate Threshold. That arbitrary parsing of your metabolic response so finely (some of these 7 zones are only a few beats wide) is what is called in engineering “False Precision”. There is no way this precision can be assumed even if one has a careful lab test.

    This is why we use a simpler zone system with the principle anchor points the AeT and the AnT. Do you really think there is meaningful distinction in the metabolic or global training effect between say 176 and 179 bpm HR. Unlikely.

    I would not get overly concerned with the HR increase you are seeing int he later reps.

    The way many top athletes in XC skiing (where pace is irrelevant) use interval training is to go as hard as they can for the prescribed time and number of reps. It turns out that long reps like 10-20 min allow only about Z3 intensity. Medium lengths like 8min will allow Z4 for the well trained, Short reps like 4 min allow Z5 effort. All these are done with a 2 minute rest interval typically.


    yesisaidyes on #17733

    This makes complete sense – thanks!

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