Three weeks is possible. It depends on a couple of things. 1) how long have you been working out? If it hasn't been very long you will see trememdous gains in the first few weeks. If you have been working out and are stuck at a plateau, try changing your routine (higher weight-low reps) that will kick start your muscles and increase growth. 2) How hard do you work out? If you want to see gains in strength in 3 weeks you had better see stars when you finish a set. Don't kill yourself but go until failure and then have a spotter help you do 2 more. 3) What do you eat? Try a protien supplement to help repair your muscles and if you are looking for a quick boost in strength and endurance try creatine. I took it once and my bench max jumped up 50 lbs in a month. It seems to allow you to work harder and longer before muscle failure. I've also heard it will improve your timed runs, but I can't back that up personally. Bottom line: you can do it, just push yourself hard, consume lots of protein, and try different routines. Oh yeah, be sure to allow a body part at least 48 hours to recover or you will fall victim to the "theory of diminishing returns". (you'll be busting your butt, but getting no results) 3 weeks will be tough, but not impossible. Good luck!
