Exactly Kieran...So don't throw away your HR monitors just yet...
Some more info from Juerg's response to Toks about HR, have fun reading:-
Part 1
I like to keep the info going on this topic. Not to discourage people in using wattage or HR only , but rather show as objectively as possible benefits and disadvantage on both of them.
Here a question I got least night.
“There are days, where I try to maintain a wattage level close to my Lactate threshold, but still slightly below. Now some days, I can't hold the wattage very long and I also can't get my heart rate up as well so both of the ideas don't work at all ( wattage as well as heart rate ) why ?
Hmm this is a situation I think any runner or cyclist has had in the years of training. Days where the body just flies and days where you just crawl along.
Well the beauty of this experience teaches us one thing for sure. We are not a motor but a physiological system.
There are some possibilities who can lead to the above situation and possibly some explanations we don't know yet.
I will in the evening try to shed light on one very interesting situation, and we very often don't think at that direction.
Here’s a hint.
You had a few busy days at work, no time to workout, you whole "plan" went belly up and you are frustrated. So finally you have been able to squeeze a 2 hour time slot and you like to pick up all your missed units and you go out after work. As usual very little food and very keen to get going.
You have one advantage:
your mind is ready, your legs are recovered and fresh, your bike is keen and your wattage meter works well, as does the polar monitor.
You even see a very high HRV at rest and you are sure it will go nicely.
Your plan: 2 hour ride just below LBP if you take HR so 145.
Or you plan to go with wattage just below LBP or a zone for that length of workout 260 wattage.
I take again a real example tested and checked just lately.
LBP by 145 / wattage at that HR 260.
Here a hint.
Your liver is half empty after a 12 hour work so app. 60 - 70 gr of glycogen left.
Your leg muscles are at a same situation so let's say 140 gr of muscle glycogen left.
So total glycogen at the start situation 200 - 210 gr.
Now start working out.
Here one more info to consider.
The VO2 ( total O2 used in this intensity 145 /260 wattage is 38 ml/kg /min
The kcal/h at that intensity is 845.
Now train by 260 wattage
or train by 145 HR .
Play through your physiological system and see what or when we may get some reactions in these 2 versions of training