I improved - so why did my LTHR drop?

Hi All,
I’m a 51yr old male, new to cycling but a seasoned endurance runner (10km+ distances). I started training with The Sufferfest in November as part of recovering from a running injury.

I took my first 4DP test in February, and my second yesterday (mid-May). Clearly my fitness has improved enormously since starting out. Over the past 3 months my FTP and MAP numbers have increased by more than 20 points, but my lactate threshold heart rate (LTHR) has dropped from 161 to 158.

I would have expected my LTHR to rise as my aerobic capacity improved. I feel fitter and can see the improvements in my workouts. So why has my LTHR dropped? Physiologically what is happening?


It was a different day.

Due to the way LTHR is estimated it is unlikely to remain steady and you’d have likely got a different result if you’d done the test the day prior, the day after or even at a different time of day.
It’s an estimate to work around, but is far more likely to be variable under single test conditions than your power output (which still would likely have been at least slightly different the day earlier, the day after etc.)

In short, don’t worry about it, especially if you’re training by power rather than heart rate.

Hey at @MartinUK ,
Welcome to the forum. What @Jon said is spot on. A difference of a few beats is not a significant difference.
Here’s are. couple of articles to check out:


It’ll be interesting to see what your numbers are on your next FF. Keep up the good work!



Your heart is not necessarily the limiting factor

Thanks everyone. As I understand it, the differences in LTHR are within the range expected for experimental error or day-to-day variance. So the slight drop means absolutely nothing, my LTHR is basically unchanged.

Thanks for taking the time to explain this. Much appreciated.