I think discussions of muscle tone on here have little to do with weight and more to do with physical (and possibly neurological??) wellbeing of the snake. Keep in mind that I'm not educated on snake illnesses or anything like that; this is just what I've gathered from reading a lot of threads here.

Imagine if a dog, or rabbit or whatever was suddenly barely able to hold itself up on its legs, and had them weak and wobbly all of a sudden after having been able to stand, sit up, and walk normally. Big warning sign, right? Well snakes are pretty much always on the ground and use a lot fewer muscle groups to move, but same principle. Low muscle tone, as would be seen in an inability or weakened ability to constrict, grip, or move properly, is a red flag in regards to the general health of your snake.

If a BP has low muscle tone, I'm assuming the signs would be as such: trouble constricting prey, holding on to things to climb or otherwise navigate on anything other than flat ground, curling/coiling up as tightly as they should be able to.

If anyone else sees any misinformation in here, please do correct me