Why are 50% of my max heart rate = 116 bpm, while the max HR is 180 ?

According to your screenshot:

- your HR zones are based on HRR% (% of Heart Rate Reserve) - hence "% Reserve" - not % of Max HR

- heart rate reserve is basically the difference between your max hr and your resting hr

- the point of setting zones based on HRR% as opposed to % Max HR is that HRR% is supposedly better correlated with your fitness (as it takes both resting HR and max HR into account, not just max HR). Some would say that % lactate threshold would be even better tho.

- your resting HR is 47 (although you have cut off this label in your screenshot)

Here's the formula for % heart rate reserve:

% HRR = (HR value - resting HR) / (max HR - resting HR)

When HR value = 114 (as per your screenshot):

% HRR = (114 - 47) / (180 - 47) = 67 / 133 ≈ 50%

You can calculate the values for each of the percentages yourself, by rearranging the formula:

% HRR = (HR value - resting HR) / (max HR - resting HR)

% HRR * (max HR - resting HR) = HR value - resting HR

% HRR * (max HR - resting HR) + resting HR = HR value

HR value = % HRR * (max HR - resting HR) + resting HR

e.g. for % HRR = 60%:

HR value = .6 * (180 - 47) + 47 = 126.8 ≈ 127 (after rounding)

This matches what's on your screenshot