How can I get warmed up to ensure that I do not suffer shoulder injuries during weight workouts?

Working up to Bigger, Stronger Muscles

Is it possible to increase muscle mass by doing more repetitions with lighter weights, or do you need to be lifting heavier weights?

It depends on your intensity level. You can increase your strength with heavier weights, but let鈥檚 say you鈥檙e capable of squatting 225 pounds for ten repetitions and that, physically, you can do no more.

If you reduce the weight to 125 pounds, but increase the reps to 20 鈥?and then complete another rep on top of that 鈥?you鈥檒l have stimulated your body to respond with increases in strength and muscle mass.

Providing you have proper rest and nutrition, you muscles will be stronger and bigger next time you train.

Of course, there are genetic limits of this, but the general rule applies to everyone.

So the answer is less about the number of reps but how much effort you put into your set.

Basic rules to follow are:

Maintain proper form
Gradually increase the weight or reps
Do most sets to 鈥?or almost to 鈥?muscular failure; in other words, until you simply can do no more.
Also, keep in mind that the upper body generally responds well to 10-12 reps; the lower body responds to 10 to 20 reps.