Power variation for same HR?

neeb

Yesterday (Monday) I had a 50min session on the tacx trainer, mainly climbing, which was exactly the same as the one I did on Saturday. However in the monday session, I managed an average power output for the climb which was about 10W more than what I managed on saturday, and a correspondingly faster time. HR was very similar, but actually very slightly higher on the Saturday (slow) session, which also felt more knackering. The problem is I have two possible explanations for this. One is that the trainer calibration wasn't the same between the sessions, although I am very careful to try to replicate roller & tyre pressure exactly. The other is that I had had nearly a week off before the Saturday session. I'd like to try to work out which of these is more likely, because if it is due to the time off then it tells me quite a lot about how my condition is affected by taking time off. The monday session was actually my best time ever, while the session two days before was significantly below my current average.

Is it possible to have a 10W+ power difference in two identical sessions two days apart with the same average HR, on exactly the same course and same conditions? Sorry if this is a stupid question. If so, what is causing this difference?

Murr X

neeb wrote:

Yesterday (Monday) I had a 50min session on the tacx trainer, mainly climbing, which was exactly the same as the one I did on Saturday. However in the monday session, I managed an average power output for the climb which was about 10W more than what I managed on saturday, and a correspondingly faster time. HR was very similar, but actually very slightly higher on the Saturday (slow) session, which also felt more knackering. The problem is I have two possible explanations for this. One is that the trainer calibration wasn't the same between the sessions, although I am very careful to try to replicate roller & tyre pressure exactly. The other is that I had had nearly a week off before the Saturday session. I'd like to try to work out which of these is more likely, because if it is due to the time off then it tells me quite a lot about how my condition is affected by taking time off. The monday session was actually my best time ever, while the session two days before was significantly below my current average.

Is it possible to have a 10W+ power difference in two identical sessions two days apart with the same average HR, on exactly the same course and same conditions? Sorry if this is a stupid question. If so, what is causing this difference?

Assuming correct calibration of the turbo, the week nearly off before the first (Saturday) session could easily have resulted in a lower power output than Mondays session for the same HR. Often after a rest week the first hard ride is not so good and yes two days later you may be considerably better and power can be noticeably higher, so yes 10watts more is normal for many.

In my experience after time off the first ride back is always inferior to the next ride - even if it is just two days later or less. I would tend to ease back into things after time off though, ie the first ride back would not be too hard then the next ride (next day or two days after first ride) would be harder, sometimes taking a few rides to get back into things depending on how long I am off the bike, a week off will generally not take much time to get back into things.

neeb

This fits with my subjective impression. It almost feels like after a week off you need the first ride to get everything working properly again, or to switch the metabolism into active mode. I wonder what it is; something to do with optimising the circulation to the muscles or something?

Of course I realised after the OP that there could be all sorts of things that could result in less power for same HR from one day to the next; presumably hydration levels for a start.

Jeff Jones

On the road, I've had significant (20W) variations in power output for an identical heartrate in head/tail/headwind sections of a TT.

Still don't know how to account for this or how to overcome it - bigger gear in the tailwind maybe? But I have a suspicion that my cadence was pretty constant, it was just the lack of resistance caused the power drop.

liversedge

HR is just very very very very very very variable!

Many factors will impact your HR. Some of which are temperature, altitude, hydration, fatigue, sleep, stimulants (e.g. caffeine).

Also, tacx aren't the most accurate and consistent devices on the planet. variances in cadence and tyre pressure alone wll skew the measured results!

Alex_Simmons/RST

neeb wrote:

The other is that I had had nearly a week off before the Saturday session. I'd like to try to work out which of these is more likely, because if it is due to the time off then it tells me quite a lot about how my condition is affected by taking time off. The monday session was actually my best time ever, while the session two days before was significantly below my current average.

Is it possible to have a 10W+ power difference in two identical sessions two days apart with the same average HR, on exactly the same course and same conditions? Sorry if this is a stupid question. If so, what is causing this difference?

Your perceived exertion and power (if accurate) are a much more reliable guide than the HR response. If it felt hard, it was hard.

Riding hard after a week off is often quite difficult and it doesn't surprise me you found it harder than a couple of days later when you had "woken the legs up" with the earlier effort.