The plan is to maintain 135-140 HR which for me is Zone 2 (relatively easy pace), but then at the last 70k of the bike HR goes down to 120-125, bringing down power as well by 30W.

In all of my ironman races there have been a significant decrease in heart rate and power in the last 70k of bike and last half of IM marathon.

Posting these if anyone can help on what could be the cause and tips to address it.

In a race I only pace the bike by HR, using power as upper limit only. The plan is to maintain 135-140 HR which for me is Zone 2 (relatively easy pace), but then at the last 70k of the bike HR goes down to 120-125, bringing down power as well by 30W.
And then in last half of marathon I again cannot raise my HR above 130.

Preparation wise I do several 5hr rides almost once a week, and high intensity workouts.

In regards to calories I consume in the bike around 1 efs liquid shot/hr (400kcal/hr).

Have a high sweat rate so I normally drink 1 water bottle every 20min and in hot races I don't pee in the whole ride or maybe only once.

So you became tired.

In all of my ironman races there have been a significant decrease in heart rate and power in the last 70k of bike and last half of IM marathon.

Posting these if anyone can help on what could be the cause and tips to address it.

In a race I only pace the bike by HR, using power as upper limit only. The plan is to maintain 135-140 HR which for me is Zone 2 (relatively easy pace), but then at the last 70k of the bike HR goes down to 120-125, bringing down power as well by 30W.
And then in last half of marathon I again cannot raise my HR above 130.

Preparation wise I do several 5hr rides almost once a week, and high intensity workouts.

In regards to calories I consume in the bike around 1 efs liquid shot/hr (400kcal/hr).

Have a high sweat rate so I normally drink 1 water bottle every 20min and in hot races I don't pee in the whole ride or maybe only once.

For me it's not like it feels harder in those last 70k. I just feel a lack of energy to push hard.

Do you think a better approach for me would be slower pacing in those initial 100k of the bike. Plan a lower HR for those?

Wouldn't the electrolytes be supplied in this case with the EFS Liquid Shot I'm taking 1 flask/hr?

Wouldn't the electrolytes be supplied in this case with the EFS Liquid Shot I'm taking 1 flask/hr?

The drop off in your sustainable power would indicate you're fitness wasn't sufficient to carry your planned power the whole distance so yes your target seemed too aggressive for you fitness on the day.

YMMV,

Hugh

If this is the case i.e. It's simply fitness, what is the way to go about addressing it. More long rides or a higher FTP.... in other words will riding at a lower IF prevent this? I've seen a similar drop off recently. My 1st 80 miles was ridden at an IF of 0.75 (i.e. Pretty good IMO) but I could only manage 0.60 in the last 32.... so any strategies to prevent this would be gratefully received....

1. An IF of .75 is probably too high of an intensity target unless you likely bike finish time is 5 hours or less.

2. If you could only average an IF of .6 for the last 32 miles the .75 target was too lofty.

3. I feel that weekly or semi-weekly rides of 3 to 4 hour rides with an IF of .80 or more are really potent stimuli for improving your 5+ hour power.

Hope that helps

Hugh