310/HR strap Calorie accuracy

I am using 610 and had stopped using the HRM strap over a year ago because it started to continuosly display lower calories as compared to previous runs with similar pace and distance, resulting obviously from HRM readings that were lower than actual. The change did not happen overtime but it seems like the strap itself just worn out and did not count every beat. The replacement strap price at Garmin local store is outrageous so I calculate calories from GC based on pace and distance, which looks ok.

Are you sure you aren't just getting fitter, resulting in a lower heart rate?

Garmin straps I've had that failed generally went one of two ways: reading 0 bpm either continually or intermittently, or spiking up to ~240bpm.

Use a replacement Polar strap. I forget which model's compatible with the Garmin transmitter but it's about 1/3 the price of a Garmin strap and so far my Polar one's lasted a lot longer too. Go-go-Garmin engineering.

1661

For me it was definitely not about getting fitter. The change you menation had first happened too but on a significantly smaller scale...
See my previous post on this over a year ago - https://forums.garmin.com/showthread.php?300421-HRM-data-erratic&p=670282#post670282

Might have gotten more response in the forerunner area of the forum? :p

The actual graph of your workout would be helpful diagnosing a problem with the strap, but 35 calories for ~3k sounds way too low.

That being said, there's a world of difference between a faulty strap generating bad data, and the question of how accurate the calorie count from a working strap is.

Post some graphs guys! :D