First, is the fitness graft adjusted for age? As a 61 year old cyclist I feel more time is required for recovery. Is this fact incorporated into the fitness graft? Strava is showing my form at -65, while Intervals is showing my form at -11. Why the difference in the Strava vs the intervals fitness grafts? Personally I feel more like a -45 form today making Strava’s graft more believable. Am I missing something. Using Intervals eFTP, and I really like the way the Intervals displays the information.
Tx. No it is not adjusted for age. The fitness and fatigue lines are derived from your training load for each activity and your FTP at the time (assuming you have a power meter, otherwise HR data is used). If your historical FTP is correct in both tools (use “Edit” on the calendar and fitness pages in Intervals.icu to set it) and Strava is set to use power only, then the charts should be very similar. I don’t know what Strava does if you choose “relative effort”.
By default Intervals.icu shows your form as a percentage of your fitness, not an absolute number like Strava. But thats not going to make up a -65 vs -11 difference.
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I’m seeing a different form number too on Strava and Intervals. Here, I see Fitness/58, Fatigue/83, Form/-25. On Strava Fitness/55, Fatigue/65, Form/-10.
And that’s using absolute values. If I use percentage, my form dips to -43% and dips into the danger zone after each long weekly Saturday group ride.
If your FTP is the same in both (including history) and everything has power and you have Strava set to power only then they should be very close. When I started with Intervals.icu 2 years ago I got a very close match with my data. Not any more because Intervals.icu estimates load from HR activities differently to Strava. I think their “relative effort” is HR based but it gives huge numbers for me that don’t seem comparable to training load from rides with power.
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I am not sure how Strava calculates Relative Effort but I nearly died with TrainerRoad Angora with IF = 0.99a and Strava has Relative Effort @ 58!
Isn’t changing the amount of days used for the calculation of fatigue/fitness a way to adjust the calculation to your age? In your case using 10 instead of 7 and 50 instead of 42? (these are numbers I made up)
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I find using TRIMP instead of time in zones makes the Strava and Intervals graphs more similar.
I’ve always taken Strava’s relative effort with a pinch of salt. Today easy 30 mile ride outside all z1/z2 HR (no power on winter bike) gives realtive effort of 44, few days ago Zwift 5 mile TT at full gas gave relative effort 39. I know there’s an inconsistency in both with and without power and distance but I know which ride took the most out of me.
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When I record HR only rides I find strava massively over estimates them compared to power/hr rides.
I would recommend considering adjusting the fatigue/fitness calculation to get it to suit you. I’d love a study on how it can be best used, especially for how age affects speed of recovery.
My personal view is really dependent on what you’re good at. I could do 500 TSS at max zone 2 and still be okay to train the next day but i would struggle to recover from 100 TSS at mostly max efforts without at least a day or 2 off. Obviously the higher TSS would increase my fitness score more.
Another other option is to keep an eye on your form - some people peak with positive numbers and some with negative. You might want to keep your negative form within -20 (the default looks like -30 is red).
I would recommend looking through your history and recall how you felt/performed/recovered from and see what your numbers are. This does rely on FTP/HR being set accurately
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