If you're already used to lifting weights, using free weights or machines won't make a noticeable difference in how much stronger you get or how fast you can push the weight after 8 weeks of training.

If you're already trained in lifting weights, whether you use free weights or machines, you'll get about the same strength gains after 8 weeks—as long as you're lifting the same amount, at the same intensity, and moving through the same range of motion.

If you're already strong and lift weights, training each muscle group either once or five times a week for eight weeks will give you about the same strength gains on the bench press, squat, and row.

No matter the order of exercises, people who were already trained got much stronger after 12 weeks of lifting — all groups improved a lot.

Whether you use machines that change resistance as you lift or keep the same weight all the way through, after 20 weeks of training, healthy men gain about the same strength and muscle size either way.

If you're already fit and lift weights, whether you do partial reps with the muscle stretched or full reps, you'll gain about the same tiny amount of strength after 12 weeks.