got my hrm today, now i know im busting a gut!
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The numbers don't tally up on Strava apart from the HR. According to the data, you only burnt 436 calories for nearly 5 mins, but with a pretty high ave HR. The power calculated is low. I seem to remember you're riding with one arm in a sling, so will be compromised in performance.
All I can suggest is to ride on HR only, so altering all the resistance settings to allow you to ride mostly in Z2 at a comfortable cadence . ignore speed and estimated power. Unfortunately for you, Zwift and many others platforms derive speed from weight, height and a power meter. From there calories can be reasonably calculated along with relative effort and training load.
Power is king, all the information gathered over many years from professionals and others has given the likes of Zwift the ability to use the data to pretty accurately reproduce speed figures (albeit in a zero wind environment). I know Zwift numbers are pretty close from knowing my abilities outdoors and the numbers Zwift give me indoors