Cardio Fitness Score (VO2 Max) impacted by wrist weights when trail running/walking?

[DoctorDoctor]

Hi everyone,

I do trail running/walking - hilly terrain - with about 3kg of wrist weights on each wrist (6kg total). My cardio score is 45, but has gone down from 48 over the past year even though I have got fitter. If I understand how the cardio score is calculated, it looks at your heart rate and your pace on flat terrain to determine a score. 

Question 1: 

Is my score wrong because of the weights I wear on my wrists? 

I'm assuming the fitbit app thinks I am slower than I should be, but the app doesn't know I'm wearing the 6kg of weights. Over the past year I have progressively increased the wrist weights and I'm wondering if that is why my cardio score has gone down.

I'm guessing the only solution is to go for a hike without the wrist weights. 

Question 2:

If I'm right, how many hikes WITHOUT wrist weights do I need to do to get an accurate Cardio Fitness Score? Will it correct itself after one hike?

Question 3:

Do I need to go for a hike on flat ground to get the Cardio Score? I think I read that somewhere. Unfortunately I have a heel injury so I tend to hike on hills with wrist weights to increase the difficulty - I can't really run and being on the flat isn't very difficult when walking. 

All knowledge appreciated.

Cheers

[MarcoGFitbit]

Hello @DoctorDoctor, welcome to the Fitbit Community, it's always a pleasure to salute new members! 

Please note that the higher your VO2 Max is the more fit you are. Fitbit will calculate this based in your resting heart rate, age, gender, weight and other personal information. Remember to wear your tracker to sleep for a better resting heart rate estimate. Now, in regards of your questions:

Question 1, in order to have a more precise estimate of your score, just as you mentioned, will need a good relationship between pace and heart rate during your runs. Since you're running with some weights it may take you more effort to run which might affect your heart rate. Individuals with higher VO2 Max have a lower heart rate while running at the same pace compared to individuals with lower VO2 Max. So, in order to have a good score, you should be able to run at a comfortable pace for at least 10 minutes and use GPS.

Question 2, the score will correct approximately after 1 week. However, the more you exercise with weights the less effort it will take as you're getting used to them, which eventually will give you a more accurate score.

Question 3, a flat ground is necessary when the tracker is trying to estimate your cardio score while running using GPS. Increasing the pace while running might help get a more accurate reading as higher-intensity activities provide a more accurate estimate. 

I hope this resolves your inquiry, if there's anything else I can do for you, please feel free to reply. 

[LZeeW]

@DoctorDoctor  I'm not sure I can give you an exact answer as to why your cardio fitness score has gone down.  But I might be able to answer a few of your questions.

Since your weight is one of the factors used in the calculation, adding 6 kg is enough to add error to the calculation.  I suspect the change would have been more dramatic if you had added all 6 kg at once. 

The single number cardio fitness score, as compared to the range, is only calculated when using the GPS connected run.  It is recommended that you run on level terrain, as you heart rate response to exercise is different on hills.  When you are taking your hikes, are you tracking them as hikes or runs?  If you have your tracker set to run, the score will be wrong because of the hills.

I don't know how many hikes it will take to show a change in your score.

IMHO, if you feel fitter, I would keep doing what you are doing, and don't fixate on your cardio fitness score.