M@L has given you a great answer. It's not a scientific formula because there are so many variables involved, just very rough estimates based on some research and looking at what other sites have used.
Sorry I don't have a more specific answer for you!
the reason i'm asking is that for the longest time, a lot of Spark members & also the folks who run the site felt that calories weren't something that could be measured as so many variables go into strength training
so .... i'm curious as to how they went about developing this.
I don't think there is much formula about it at all. It doesn't really seem to vary much between large and small muscles, or vary by weight, number of reps, etc.
But one well known study puts the metabolic gain from a regular program of lifting at about 150 calories per day. The very rough calorie estimates from Spark would give you something broadly consistent with this.
I don't think there is much scientific rigour about it, but if it encourages people to take up ST, well, its something I can live with.
SparkPeople, SparkCoach, SparkPages, SparkPoints, SparkDiet, SparkAmerica, SparkRecipes, DailySpark, and other marks are trademarks of SparkPeople, Inc. All Rights Reserved.
SPARKPEOPLE is a registered trademark of SparkPeople, Inc. in the United States, European Union, Canada, and Australia. All rights reserved.