I’ve noticed that during long ‘Ventilatory Theshold 1’ (VT1) type workouts I pretty much always achieve negative Heart Rate decoupling. What I mean is, there is some de minimus increase in HR during the first 60 to 90 minutes but then HR trends back down to some lower plateau for the rest of the workout.
This only happens when I’m at or around VT1. For instance, during Gibraltor HR started trending up at the beginning of the workout and continued to trend up right through to the end. Started the workout at 78% of max HR & wound up working at 92% of max HR. Gibraltor, while far from an intense workout, is well & truly ABOVE VT1. So I can’t hold that much power for an extended period of time.
But if I just set power to 55% of MAP & start pedalling HR will peak in 30 to 40 minutes and then trend down over the next 45 minutes to an hour.
I guess that’s one way to know you’re at or below VT1?
I even see negative decoupling on 40-50 minute intervals at upper sweet spot / threshold intensity. For example 3 years ago around this time my aerobic fitness was very high. I was doing longer ss/ftp intervals on an outdoor segment, take a look:
And yes my FTP was set correctly, those IF values are good. For reference my LTHR is 162bpm. Without looking I’m sure some of the lower HR were due to functional overtraining as I was going really hard a lot of the time.
On that other thread I speculated (based on Alan Couzens article) that despite doing some over threshold work on warmup, some less efficient fast twitch fibers were still being used early on in the interval, and then most of the fast twitch stopped and more efficient slow twitch fibers took over. In other words, my slow twitch went “all in” and that was reason for negative decoupling. Or its because I was training so hard around that timeframe, and my HR response was blunted. But honestly I have no clue as to why, it just is what it is.
I get negative decoupling quite a bit, a couple of days ago I got -3.2% on Pettit and I’m under 1% on endurance stuff. And I got some negative overall values during my last week of SSB2 HV. For me, I think it’s a bit of a function of settling into a workout after an interval sometimes. Or I may just be super fit lol
Pettit and my table above (40-55 minutes at threshold) are one of the reasons I believe it pays to understand the reason why Joe Friel says use decoupling on 2-4 hours. That Alan Couzens article is gold. Don’t waste time or get a false sense of “aerobic fitness” if decoupling is low on 1 or 1.5 or 2 hour workouts. On some other thread I had 0% at 2 hours of lower tempo (78%), all that says to me is “go out and try that for 4 continuous hours” and then look at decoupling.
Go out and do 2 hours at 65% endurance or 75% upper endurance, and then look at decoupling. If you have little or no decoupling at 2 hours, go longer. If you can, do 4 hours. If all you do is 45 minute crits then 2 hour decoupling test is likely good enough. If you do longer road races or condos then 2 hour decoupling is too short and you need to go long (4 hours).
Just having an ‘off forum’ conversation about this topic and some muscle oxygenation data I took a while back. We notice that if you just hope on the trainer and start pedalling at some low wattage (let’s say 75W) SMo2 gradually goes up until it reaches a plateau somewhere in the mid 80’s after about 35 minutes.
I suspect that more than anything this is what is happening in my data. After a half hour or so the blood’s ability to carry oxygen to the working muscle is just reaching it’s peak.
Here is my on forum discussion of the same, without the SMo2 data:
At constant power you can clearly see HR rising up until 30 minute mark. Then during last 60 minutes “work interval” my HR and Power track within 1%.
I always throw out the first 15-30 minutes for any tracking of EF and aerobic decoupling, including these quick weekly “Mesa Aerobic check ins.” For outside rides I’m doing more anaerobic work leaving the city, seem to warm up quicker, and for convenience I simply hit lap button after the 15-20 minutes needed to get out of town.
IMO HR coupling or decoupling is more a function of temperature, hydration, level of arousal, and fueling differences rather than necessarily any discernible marker of positive or negative aerobic fitness.
To me, this just says that I ate and drank enough.
You will get anaerobic contribution from all of the various systems until lactate production and shuttling takes over more fully, but your fiber type speculation is incorrect. Muscle fiber recruitment doesn’t start from strongest to weakest, it’s the inverse.
yes I completely agree. What I don’t understand is that after two 30-60 second anaerobic efforts just before leaving town and pushing the lap button, how long does it take for those fast twitch fibers to disengage? Prior to starting the segment above, I’m doing a longer 5-10 minute ‘clearing’ effort that usually finishes with two strong/short anaerobic efforts. Then maybe 30-120 second recovery, hit the lap button, and do the 15 mile segment. Because the segment was preceded by a strong anaerobic effort, how soon do the fast twitch disengage? If it takes 5 or 10 or 15 minutes, that could reveal itself as negative decoupling. I wasn’t trying to suggest fast twitch are recruited first, I simply didn’t explain what happens prior to the start of the interval.
Thanks. I’m always curious why negative decoupling happens, just speculating a bit to blow off some steam from work stress. Had negative decoupling tonight on 90 minute aerobic ride but I think it was letting go the stress of the day/week. It is what it is. Ride on.
It’s an interesting phenomenon since it’s the opposite of what should be happening in the body, all things held equal, but i’ve never been able to draw any real conclusions from negative decoupling.
Even a reduction in positive decoupling for harder efforts across weeks could be attributed to increases in stroke volume. For example, my threshold heart rate drops 6-8bpm over the course of the season.
I know there are some strong believers in heart rate guided training and the associated insights, but it’s just never made sense to me and always seems secondary to the work rate.
Just wanted to revive this old topic. I do ultra endurance/audaxing, and I’ve noticed that my heart rate drops a lot several hours into a ride. For a while I’ve been thinking that just means I’m exhausted and slow, but on the 34 hour ride last weekend, I looked more into it.
For example, if I average 170 W 2 hours into the ride, my heart rate is quite high at 147 bpm. After 8 hours, my HR is 145 bpm even if I do 177 W. And then, after 28 hours, I’ved eased off a little to 158 W, but my HR is only 123 bpm!
This seems like a significant negative decoupling. Has anybody experienced something similar? I wonder what the physiological explanation is.
That same descending heart rate phenomenon seems to be quite common in 12+ hour cycling events. I definitely don’t understand why it seems to be such a universal phenomenon.
But one thing to think about! In my last 24 hour I held a pretty steady heart rate for about 5 hours & then it started to drop. The descent in HR started at about sunset. The next day at sunrise HR started to climb back up but never reached as high as I was able to maintain during the first 150 miles of the race.
In my last 12 hour I was able to maintain ~84% max HR for 8 hours before HR started to drop. Obviously pacing is a lot different in a 12 hour event.
But another thing to consider is just absolute temp during the ride. The 12 hour ride was 60 degree weather pretty much right the way through. The 24 hour ride was mid 80’s during the day and much cooler through the night. Below 60 degrees for most of the night. In that case fatigue definitely modulated HR but temperature also had a big impact.
So part of the puzzle is probably just the fact that we generally start in the morning, race through the heat of the day, then into the night. If you maintain a constant effort during the day & into the night you should see your HR drop just because temperature is also dropping.
Thanks for letting me know it’s a common phenomenon. Your thoughts on the impact of temperature are interesting, but I should add that on my ride above we had rain and low temperatures on the first half, and then much nicer weather on the second day!