I did a 16k run yesterday and just noticed something interesting.
For the first 10k, I ran about marathon pace, and then did four 1k repeats at something like 10k pace with a short walk-to-jog recovery in between.
As expected over the whole session my heart rate gradually increased, then increased a bit more over each of the first 3 intervals. Into the 4th interval my heart rate stayed lower. See the chart and the highlighted areas. Heart rate is red, pace is blue.
For reference my average was 138bpm, at the 2k point it was about 130, the first 3 intervals was between 150-160. And in the highlighted section it was in the 140s. But this was actually my fastest 1k interval.
No gels or water was taken. Almost never use caffeine, in any drink or gel.
I didn’t feel light headed, nothing felt wrong. So what in the world did I do to keep my heart so low? Was it because I mentally knew I was getting close to home and was just more chill? I’m less likely to believe it was just a random watch fluke, since it coincided with my hardest interval. I certainly didn’t feel like I was crashing or bonking or anything.
What type of Heart Rate Monitor do you use? Wrist based? Chest Strap? Other?
That looks like the HRM jumped. As you already stated it looks like a random watch fluke.
I was using the Fenix 6. I realize the wrist is not as accurate as the chest. I have a chest monitor, but haven’t used it lately.
My point was that the entire last interval was harder and the heart rate dropped (red). That seems weird.
It just randomly drops and stays consistently down for the entire interval?
My working theory is my rest before the last interval was an extra 30 seconds and that kept my heart low enough and it just stayed lower during the harder effort.
That’s a pretty big implication for me in taking an extra 30 second break in a middle of a big run to completely reset my heart rate.
I do almost all my training based on HR. It’s taken me 2 years of frustration to (mostly) figure it out, and I’m still learning
HR training is most reliable / consistent when my “inputs” are consistent - things like sleep, weather and also hydration
If I start to get dehydrated for example, mid ride, my HR lags
Given it was the end of a run, and your HR dropped - id guess you were under hydrated (or maybe even not enough electrolytes)
Also, get rid of watch based HRM (unless it’s the new Pixie), they just aren’t reliable
Extra rest also plays a role. Hard to say if that’s responsible for it, as you would expect to see a similar rise as you did on interval #1, which didn’t happen
I don’t think its probable that 30 seconds rest made such a difference in HR, you might see it start much lower, but it would jump right back up, especially so late in the session. Much more likely the wrist HR accuracy. I find it to be total crap.
If you don’t like chest strap, you can get an optical sensor (e.g. polar OH1) and place it on your bicep or forearm. For me that fixed the issues of chest strap (chafing and inaccuracy due to static electricity from shirt) and I have no accuracy issues.
Seems like it could be bad data. Did you do anything differently on the recovery before the last rep? You said you were doing a short walk jog? How short are we talking? Walking can really let the HR come down.
10 second walk, transition into a jog then start up again. Might have been 30s walk in this last one. I’m curious about that aspect though. If you can just throw a slightly longer walk break at 20k and 30k in your IM marathon and the heart rate stays lower instead of immediately climbing back up like normal that’s totally worth it.
BlockquoteI was using the Fenix 6. I realize the wrist is not as accurate as the chest. I have a chest monitor, but haven’t used it lately.
Ya, the wrist monitor data jumps around quite a bit in my experience. It is pretty common on a steady state run for me to see the heart rate to stabilize at something like 140 BPM 1-2 miles into a run and hold there for 40 minutes of a run then jump up to something like 155 BPM when I haven’t changed anything in terms of my pace, perceived effort, etc. Also, I could we at 140 BPM for an easy recover run one day, then, 135 BPM for the same easy recover run and the same pace the next day, and 150 BPM the day after that. I don’t use the wrist monitors for any type of HR training. it isn’t repeatable. Luckily I have other ways to pace that don’t require the heart rate. During a workout or race 9 times out of 10 I can guess what my pace is without looking at the GPS watch based off my perceived effort and then be within 5 sec/mi of my metered GPS pace when I check the watch. I also can tell when I have cross from Zone 2 to Zone 3 pace. As soon as I go from easy breathing to labored breathing I look at my heartrate reading on the watch (chest strap monitored, NOT wrist monitored) and every time my hear rate is within 1 BPM of my transitional heart rate from Z2 to Z3. So…I don’t get hung up on HR readings. When I have the Chest Strap monitor on I can use Heart Rate to pace off of. When I have the wrist monitor I have to used perceived effort. Anything odd in the readings is due to the monitor not the actual heart rate.
Would assume that deep into a race that a walk break wouldn’t really be able to curb an elevated HR in the same way as a shorter workout you do when you’re fresh. I think it’s a viable strategy for a lot of athletes to incorporate walk breaks (traditional approach is walking aid stations) throughout the IM run. You’re basically making sure you’ll be able to cover the entire distance because you’re monitoring your energy throughout. Not going to get the same benefit later in the run. HR will come down, of course, but it might be too late for that to allow you to power through after that. HR @ 20k and 30k @ the same pace you started at should be higher later in the race. Effort increases, while pace stays the same. The more frequent walk breaks probably better allow for a more steady HR when you’re running because you’re stopping before it gets to the point where you’ve been running for a prolonged amount of time close to your IM upper limit. Decreasing your chances of bonking if done right. You’re not really walking & then hammering. You know what the run pace should be each run segment to have the kind of race you know you’ve trained for.
whenever my HRM looks weird, I take my pulse manually and count beats. It’s always the HRM malfunctioning, my HR is always what RPE suggests it would be.
The only exception to this is episodes of afib…
Yeah OP maybe for your next similar workout, take manual pulse right after each rep (10s & then multiply by 6). I do that every now & then swimming. I work levels in the pool (L1 >>> L5, 1 = ez, 5 = all-out). I’ll have longer reps like 3x1k L1, L2, L3. Take a manual pulse after each just to make sure the HR follows appropriately since watch data is trash in the pool (use strap biking/running).
