There is no reason to look at your heart rate during a race that short.

If the other guy is running faster, you need to drop in right behind him and hang on as long as you can. If you see any weakness, surge ahead and drop him.

I'd say pushing yourself to run hard in a sprint has both a physical and mental aspect.

I agree with other poster - forget HR. The fact that your heart-rate was lower could just as well be a side effect of you being more fatigued going in, or you "mentally" giving up.

In a sprint, instead of thinking of HR, you should instead be asking - am i throwing up? If not - run harder! :) Also - I should add that I'm like you a strong cyclist/weak runner. Don't let this get you thinking you have to be drobbed by anyone passing you! Stop thinking - run!

I had this experience two years ago, where I did to similar sprints on two sucessive weekends. The first one, I came out of T2 in 3-4th. Some other guy - whom I was sure was a better runner than me - passed me during the first 1k, and I didnt hang on (didnt feel like I could). I ended up half- jogging (felt like i was pushing, but kinda mentally gave up) in for a run split of 20:30. Next weekend, excact same thing happened. Same guy came up to me after 1k on the run. I decided to fuck it and run with him. To my surprise, it felt less hard than I'd thought, and he didn't drop me. I ended up with a 19:20 run split and beating him in a sprint finish:) Fantastic experience! In this last race I was like the guy you described below - lying down gasping for air. The first weekend? Not so much..

Depending how fast you are a 5km TT might take 15mins-25mins (since you were in contention I'm assuming you're at the quick end of the ranges)
A sprint race might take 55mins to 80mins.
If you were able to maintain the same intensity during a race run leg that you do on a standalone 5km, I'd think the standalone 5km was not at your max pace. Probably more reasonable to be trying to match your 10km intensity. 10km is still shorter than the sprint but then, it's not a straight comparison anyway.

When you remove all the noise, it sounds like a mental loss. The mind will shut down before the body will.

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just your average age grouper . no one special . no scientific knowledge . just having fun.

What were the two 5K splits?

I agree with this but it is prolly more comparable to a 10 mile effort as far as HR is concerned depending if your cycling and running HRs are similar. Its just that an all out 55-80 min run usually has side effects other than high HR.

Actual speed also matters like others have said. A 19:30 and a 20:15 are going to have different stride length, arm swing, and downhills are going to be more recovery. The tri might also have had more turnarounds? I have found out a long time ago that my HR dropped when I would see that cone bc I knew I would have to slow down anyway.

I dont think it is much to worry about. Maybe trying to quicken your stride during a tri split might help the pace and bump the HR to what you can manage for that effort if you still think they are too far apart which is hard to tell.

Your ability to hammer near-max HR at the end of races depends not only on how hard you try, but how fit you are in that sport.

It's because with better muscular endurance in the legs for running, your legs will be able to propel you to higher HRs. Just imagine if you could swap out your bike-spent legs for fresh new superlegs from a trained 5k Olympian at the end of T2. You'd be able to hammer a super painful nearmax HR for quite awhile.

Then compare with swapping your legs out for fresh legs from a below-avg AGer. Even if you do go all-out, the legs will limit how hard you can push, even if you feel like you're going 'all-out.'

This is also why that in track workouts with a lot of rookies or beginners, a set of what should be crushingly difficult 6 x 800s on the track, often look like they're easy jogging it, as they're barely even huffing and puffing. They're actually going all-out as instructed - it's just that their legs can't demand enough from their VO2 system to sustain it for 6 x 800. Whereas a strong experienced runner might sound like they're literally going to die on the last one,even if they recover faster overall.

Assuming you hammered the bike your numbers look reasonable. I'm guessing sprint HR numbers should line up more with 10k numbers. Yeah, you're running a 5k, but that's after ~30 minutes hammering a bike.

What about during an Olympic?...monitor HR or just try to hang on?

Try to hang on. Train by numbers. Race by feel.

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Trust me I’m a doctor!
Well, I have a PhD :-)

Bingo!

Pretty slow, 22.30 for the sprint and 20.40 for the 5km TT. Do most people get close to their 5km TT in a sprint? Most of the top guys in my AG are doing 18s, 19s, I can only compete because I can swim and bike. I think for me, there is definitely a mental thing going on. I push myself hard in any sport, but I sometimes wonder if I'm not pushing hard enough sometimes in running. The other day we were doing 1km repeats in training, I was flying along, HR going through the roof and I felt like I was drowning, with a desperate desire to stop, I guess I need to feel like that in a race? I certainly didn't feel like that in the tri. Pretty frustrating, I suppose I need to find a way of putting up with the pain, it's pretty horrendous though.. I wonder does everyone hurt that much?

I would not say that's slow but there is too much spread between the two times.

I would be looking at less than 90 seconds slower than your 5K time.

Now if you backed off on the bike you might gain some time on the run but it would probably be a wash (or a loss) on the total time.

Perhaps more concentration on your speed for the run during a tri is in order. Maybe some practice on the skill would help as well.

Different from what others have said, I have used HR as a low limit in short course racing. You know what you have done, try to better it next time, see what that gets you.

Definitely use all of the advise here to make yourself better.

Any chance your HRM was picking up your run cadence?

If not, you probabky could have gone deeper based on the previous run. But hey, I will never be first into T2, so there's that...

I haven't done any sprint triathlons, jumped in at Olympic and went from there, but I have done lots of sprint duathlons. Typically 3km run, 20km bike, 3km run or something similar. I'm doing 6km of running in total with a spot of cycling in the middle. I'd be happy enough with a run pace about 20 sec/km slower than my 5k pace. That race will take me a little over an hour and my HR is pretty high throughout. No way I can compete with the pace I can do on a 21 minute standalone run.
From memory, last time I did a 5k and a sprint duathlon within weeks of each other my, I think my 5k average HR was 173bpm and for the sprint duathlon it was 165bpm. I would pace it so that I have a tiny bit in reserve for the last run and my HR on the run is slightly higher than the bike so my average HR for each leg might be something like: 1st Run - 166bpm, Bike - 162bpm, 2nd Run - 169bpm.

I did a big sprint at the weekend and HRM failed, but I had a mini break-through in that I ran a 5km season PB. I've been reading a bit about dealing with pain and not treating it as a negative thing and that kind of helped. The weather was really hot, no wind, it didn't feel good out there. I ran a quick first 1km, possibly a little too quick, then between kms 2 and 3 the pain and negative thoughts came on, "I can't do this" "I hate this sport" "I can't breathe" "I need to stop" "where the fuck is the turn around point" "oh shit my pace is slowing" etc etc I get to the point I feel like I'm drowning and almost panicking for breath, but this time I just held on. The pain didn't get better, but it didn't get worse and became manageable, just. kms 1, 2,3, were all 4.05 - 4.07s, I had a little blip km 4 as I hit a small hill, got overtaken by someone in my age group and had a mini mental slump, 4.20, then rallied and last km was 3.40, overtaking the guy. Disappointed with 9th position, but these sprints are so competitive, one or two small mistakes can cost you a few places. I made a mistake in the swim which cost me close to a minute. But I wouldn't have made the podium anyway. Thanks for the advice.