Hi ​@Review, compare the heart rate of both runs. The higher it gets the higher is the effort score. (And very hot weather definitely increases the heart rate.)

Thanks - that is helpful. Though the RE was much higher compared to an identical run with similar average heart rate….25 cf 100... but I guess the impact is subtle and hydration levels can have an impact too. The higher RE score feels anomalous but I will live with it!

I am experiencing something similar - for about a week now all of the runs are recording a relative effort of about 3 times what they usually do - same heart rate, same pace - I am using an Apple Watch Ultra 2 - looks like you are too - I wonder if there is a new bug that popped up?

​@Review  There were reports from some users that Strava changed their max heart rate without consent on

. Could you check your settings if you are affected?