The amount of muscle a male weightlifter can gain from lifting weights will depend on a variety of factors, including age, genetics, diet, and exercise routine. Generally, male weightlifters who engage in regular strength training can expect to gain muscle mass at a rate of about 0.5 to 2 pounds per month. However, the rate of muscle gain may slow over time as the body becomes more adapted to the exercise routine. Additionally, once an individual reaches their genetic potential for muscle growth, further gains will be more difficult to achieve. It's important to note that using steroids or other performance-enhancing drugs to gain muscle mass is illegal and can have serious health consequences. A healthy and balanced diet along with consistent strength training is the best way to promote muscle growth in a safe and sustainable way.