Is it possible to build muscle while on reta?

It really depends on several factors. Beginners to lifting can add some muscle, but that potential drops quickly, especially if you're running a big calorie deficit like it seems you are. Building noticeable size generally needs a surplus or at least maintenance for recomp. Fast weight drops usually mean losing muscle along with fat, which is why hitting calorie goals matters instead of undereating.

Plenty of strength athletes continue building muscle on reta. The ones I know mainly use it to quiet food noise and keep meals clean, plus they mention some metabolic perks. A trainer can suggest movements that work around back limitations. Many non-acute back issues can still be trained with progressive overload and controlled tempos. I've rehabbed my own back problems by starting with bodyweight squats, slow negatives, and limited range before adding weight again. Worth talking to a coach about options.

You've dropped 40 pounds in roughly 12 weeks? That's over 3 pounds a week, which feels pretty aggressive.

You can definitely lose fat and gain muscle at the same time on reta. I'm doing it. Hit one gram of protein per pound of lean body weight daily, train properly, sleep well, and aim for 1 to 1.5 pounds lost per week. You're dropping too quickly right now.

A calorie surplus is usually needed to add muscle, so if you can manage that on reta then yes, people have done it. Even in a deficit you can still get stronger, improve technique, and build fitness. Due to an ankle issue I've skipped cardio for months and spent more time lifting, and my numbers have gone up. Strength and size aren't completely the same thing.

Most people accept that adding muscle in a deficit while dropping weight fast is nearly impossible. Exceptions often involve testosterone or other anabolics plus growth hormone or similar compounds that offset the muscle-wasting effects of rapid loss and GLP-1s. That doesn't mean skipping strength work though. You need it plus enough protein to limit how much muscle you lose, and keep weekly loss under 1 percent of body weight.

Some sensible resistance training helps limit muscle loss while the weight comes off. Holding on to what you have is a realistic and useful goal during a cut.

This sounds like a body recomp goal. If you're new to lifting it's much more doable than for someone who's trained steadily for years. Newbie gains can happen pretty easily if you don't lose more than about 3 pounds a week. Are you after muscle mainly for looks or for function and health?

Resistance bands could work as an alternative to weights. You can create effective routines with them that avoid heavy impact, and over time they can strengthen stabilizing muscles that help with back issues.

I came across an article on ScienceAlert about creatine. It mentioned that beyond gym use for recovery, new findings suggest it might help preserve muscle even without training, and could support the body and brain in other ways too.

Yes, it's doable. I've managed it.

I did the same and I'm down 41 pounds since mid-June, though GH and TRT helped.

As someone new to lifting you're set up to respond well to a solid program. The catch is that a deficit makes adding muscle harder until you reach maintenance and can increase calories. Lifting will still shift the weight you lose toward fat rather than muscle though. That's reliable. I followed that approach for the same reasons. With appetite suppressed and aiming for visible abs around 10-12 percent body fat, energy and motivation for training are lower. I'm not a beginner and have lifted most of my life, so a year off wasn't a big deal. Getting muscle back after a break is usually straightforward once eating and energy return to normal.

I had back pain in my twenties. Around thirty I started deadlifting despite warnings it would hurt my back, and the pain actually went away. I was in a similar spot when heavier and lost most of the weight before these meds existed. I wish I'd known more about body composition then. Now I see every phase as either a cut or a bulk. You're either adding weight and muscle or dropping fat while keeping muscle. You might not think that way yet, but once you're leaner you'll probably wish you'd done more to hold on to the muscle and connective tissue you have at your current weight. I used to hike at 250 pounds and had big calves as a result. I lost a lot of that by not squatting or deadlifting during the cut. If a trainer is what gets you under a bar, go for it, but do the lifting.