Q: Under a safe program, how long does it take to gain a pound of muscle (assuming approximately 40 minutes of weight training with moderate to heavy weights)?

A: It'll vary a lot depending on sex, age, physical condition and genetic predispositions. Assuming an average person who is conservatively overeating to support muscle gain, but to minimize fat gain, here are some rough numbers:

• Young men 16-25: 0.5-1.0 pound/week for the first 4 months of weight training, 0.5 pounds/week for the remainder of 1st year, 0.3 pounds per week for the 2nd year, 0.2 pounds/week and less for training past 2nd year.
• Men after 25: 0.5-1.0 pounds/week for the first 4 months of weight training, 0.3 pounds/week for remainder of 1st year, 0.2 pounds/week for the 2nd year, 0.1 pounds/week and less for training past 2nd year.
• Women: 0.3-0.5 pounds per week for the first 4 months of weight training, 0.1-0.2 pounds for remainder of 1st year, 0.1 pounds and less for training past 1st year.

So you can see that an average untrained young man can expect to gain 25 pounds of muscle or so in the first year. In practice this rarely happens because few people follow the good diet needed to support such aggressive muscle gain and few people follow good full-body workout routines (ignoring leg and back muscles is common which cuts out over half of their potential muscle mass gains). But it is definitely doable if you put your mind to it!