Why suppressed HR after high intensity workout?

When I work out at around 190-200W my HR is usually around 140-150. I have been doing some high intensity workouts lately (4x4min, Zone 5 Coggan/Ric). The day after a workout like this my HR at 190-200W is down to 120-130, at least for the first half of the workout, it might come a bit at the end (e.g. 130-140).

I know that it is normal to have a suppressed HR after high intensity workouts, but what is the reason for this? I can think of several explanations:

1) Stroke volume has actually temporarily increased (fewer beats necessary)
2) My blood transports more oxygen pr ml, so less blood is needed
3) My body is trying to tell me to slow down, "holding back" on my HR so that I feel fatigue sooner for any given intensity
4) My muscles somehow extract more of the oxygen from my blood, so less blood is needed

Does any of these have anything to do with this phenomena? Any other reasons for the suppressed heart rate?

 

My guess... Probably #1 due to an increase in plasma volume.

 

Hi CycleFast,
Do you have the same Perceived Exertion the day after while doing the same workout. Your description is exactly the same as mine, but for me, the RPE
is the same, only HR lower....
This happens to me, even at the same workout.. i.e: The cool-down at the same Watts as the warm-up but 10 beats/minute lowered HR.
I'd like to know also some physiological explanation

Cheers

Oscar

 

Hi Oscar,
Yes, the same Watt, and pretty much the same PE.

It's well known (and is pointed out throughout this forum by many knowledgeable people) that heart rate responds this way, but it doesn't seem like anyone really knows why it is so?

_________
CycleFast

 

The ultimate question is... are we training OK then?

or better put:

'Is this a sign of good training and not of over/under training?'

I'm just a recreational rider, but enjoy training (and the physiological theory also) a lot. At the begining of the season I'm always jumping through my LT even without trying and at the end If I want to go over LT, I must really strugle to do it, but the PE, let's say at 165 (LT) at the beginning and at maybe 155 at the end of season is the same and Wattage too. With Resting HR it's the same:
55at the beginning season and maybe 40-45 at the end. I always have this doubt: 'Is this a sign of a tired/overtrained heart or a sign of quality training?'

Any wise words apreciated

 

I also experience this. After a speedwork workout (10 second sprints at 300% MAP, 4 minutes off, 10 reps) the next day I did 2x20. RPE, power output was good, but HR was 10 beats lower!

It is impossible to think that it is overtraining, nor fatigue as I schedule like this all year. But, I have only recently started using a power meter. Before Power, I would have went home seeing that my HR didn't respond. Now, I don't see HR until afterwards.

It may be short term fatigue, but I doubt it. We're only talking two 1-hour workouts on consecutive days after a season of 10-15 hour weeks.

 

Thanks for your input!

However, I didn't quite get this one. Are you saying the #1 reason for suppressed HR is an increase in plasma volume, or are you saying my #1 reason (increased stroke volume) is the correct one, and the reason why stroke volume has increased is because of increased plasma volume?

(Was that clear?)

 

Stroke volume increases with increases in plasma volume.

Andy C can probably speak to this better than anyone.

Some interesting reads...

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?CMD=search&DB=pubmed

 

I think it's more likely to be a shift in the balance of parasympathetic and sympathetic activation, although I (probably incorrectly) invoked this one recently and was gently corrected by Andy. There are a number of proposed markers of overreaching / overtraining including disturbances in normal hormonal output, but there isn't great evidence for any of them really.

L.

 

Thank you for your comments.

However, the issue for me is not overreaching/overtraining, but why HR is lower the day after a high intensity workout, even though I'm not in an overreaching/overtraining state.

I've read elsewhere on the forum that it is quite normal (and expected) that HR is lower the day after a high intensity workout (I think also Ric has mentioned this several times).

Increased plasma volume seemed reasonable to me, since increased plasma volume means increased heart stroke volume, which in turn means lower HR for any given intensity.

I don't know, it could also have something to do with parasympathetic and sympathetic activation, but I'm not so sure overtraining/overreaching is an issue here... (?)

_________
CycleFast

 

I understand what you're saying, and wasn't implying that you are overtrained. I would regard a case of suppressed HR due to fatigue as a very mild case of overreaching- a desirable thing if you wish to improve. Many people mistakenly use the terms interchangeably (overreaching / overtraining). Increased plasma volume *is* a training adaptation, but a more chronic effect that the one you are describing: i.e. increased plasma volume (unless due to infusion) would generally cause your HR to be lower all the time which is not really what you were describing (or were you?).

L.

 

What I am describing is a "short-term" suppressed HR, e.g. it could look something like this:

Day 1: Zone 1, 180-200W, HR=140-150
Day 2: Zone 1 + 4x4min Zone 5 (VO2max intervals)
Day 3: Zone 1, 180-200W, HR=120-135
Day 4: Rest
Day 5: Zone 1, 180-200W HR=140-150

I don't know if the reason is temporarily increased plasma volume, parasympathetic and sympathetic activation, or something else, but if it is *not* increased plasma volume, wouldn't that mean that heart stroke volume is *not* increased at Day 3, and therefore a lower HR (120-135bpm at same power) would actually give me a small oxygen debt compared to day 1 since I'm working at the same power (but with less cardiac output)?

(was that last question clear?)

_________
CycleFast

 

I might also add to my previous post that I have observed this systematically, it's not just a one-time observation.

_________
CycleFast

 

Absolutely. Personally I think it's reduced sympathetic activation due to short-term fatigue. I can't think of a reason why plasma volume would acutely increase as a short-term result of one session amongst many, if you get me my drift. You are absolutely right though, stroke volume would have to go up to maintatin cardiac output at the lower HR but I don't think plasma volume expansion is the reason. Stroke volume would simply rise by necessity (as a result of reduced HR rather than the cause of it). This is one of the reasons that HR can be unreliable. A number of physiological and hormonal factors can alter stroke volume and HR. Also people experience different versions of the same phenomenon when they are tired; e.g. some people have higher HRs when they are tired probably due to reduced SNS activity, lower levels of circulating epinephrine etc. although in this case I'd be just as likely to believe that they are simply dehydrated (reduced plasma volume).

L.

 

Thanks again for your comments, this really is very interesting.

I have started to wonder though, what *is* parasympathetic and sympathetic activation? What is it, and why does it occur?

_________
CycleFast

 

I'm afraid I might have to refer you to a good exercise physiology textbook for that one, but basically they are two discrete systems which co-jointly contribute to governing a number of physiological systems (including heart rate). I've attached an image from McArdle, Katch and Katch but it's a bit difficult to see. If I get a second I'll scan it in a bit better.

L.

 

Well, I actually have the MaArdle, Katch and Katch textbook, so I guess I'll be doing some reading there tonight.

thanks again for your input

_________
cycleFast