Of course a lb of fat and a lb of muscle weigh the same, they are both a lb! But I'm given to believe that when you take the same mass,
for example a 12" square of fat and a 12" square of muscle, the muscle will weigh more
from me phone
Absolutely right. For the same volume the muscle would weigh much more than the fat. That's how we can sometimes lose no weight, even gain a little weight yet our clothes feel bigger. We weigh the same, but the volume taken up by the muscle is less so we are smaller but not always lighter.
Unless the OP has been using resistance training to increase the size of their musculature, then its unlikely that their muscles are getting bigger. Unless you increase the load on the muscle fibres causing them to break down, they will not have to get bigger to deal with the new load. For instance, if you can lift a fifty pound bag of spuds even though it feels a little heavy, your muscles will adapt to be able to lift 50 pounds. If you want them to get bigger and stronger you'd need to try to pick up 55 pounds. That's what resistance training is all about. You gradually increase the load over a short period of time and as a result you get stronger and your muscles bigger
The OP might just not be eating enough. As daft as it seems if when on a diet like we are you want to start exercising rigorously, in order to lse weight you need to increase what you take in to give your body the fuel it needs
Say your body needs 900 calories a day just to fuel it. If you then take 45 minutes of heavy cardio exercise (Say a spin class) burning 400 calories, your body only has 500 calories to fuel it. So it shuts down and holds onto its fat stores. So you'd need to eat at east 400 calories more to give your body the fuel it needs to stay in the 900 minimum per day range.
That and making sure you vary your exercise routine each week, and include resistance exercise to maintain lean body mass, are important if you want to carry on losing weight. It might sound like exercise is bad for weight loss, but of course its not bad at all, it raises your metabolism for hours after you've stopped exercising so you are burning fat stores even while at rest post exercise, but you want your body to use these stores so you lose fat as it uses the proteins we eat to repair our bodies and keep us strong
Get the gym to measure your body fat percentage and musculature and use these as a measure of your progress. That's a far better measure than just weighing yourself or BMI. Keep it up you're doing the right thing