Energy balance

Despite significant losses in absolute muscle strength and lean mass, relative muscle strength (strength per unit of body weight or lean mass) and physical function (sit-to-stand time, 6-minute walk distance) improve significantly within one year of metabolic/bariatric surgery, regardless of the specific surgical procedure.

You will lose some muscle mass and absolute strength after surgery, which is normal. However, because you are losing a lot of body weight, your relative strength (strength for your body size) and physical function (walking, standing up) will likely improve. Focus on maintaining muscle through protein intake and light activity rather than fearing the inevitable loss.