When you sleep more, your body is able to produce higher amounts of testosterone. Testosterone plays a vital part in getting bigger and stronger. 

Without a good amount of sleep,

your testosterone will be lower and you will be less likely to develop your body into a Spartan level of perfection (like you probably want). 

When you are working out and lifting weights, you are actually tearing and breaking down muscle. You only grow larger muscles during the recovery phase (which requires sleep). They actually heal tougher and larger. 

Guess

what happens when you don’t get enough shut eye? That’s right, both muscle and strength are stuck at a stand-still. Plus, you could end up hurting yourself during your next

workout since the muscles have not healed up properly.

Food (nutrition) plays an equally important part to weight lifting in muscle gain. You need to be putting bodyweight-specific amounts of protein and carbs into your body in order to grow

your muscles. 

Get enough sleep, and your body will produce chemicals like leptin that better control your body's response to food. Your body will say "I'm full," and you'll be

more likely to stick to your diet plan.  

If you don't sleep, you will end up eating extra food and it will lead to the wrong kind of weight gain

(the dreaded fat). 

Lifting heavy weight and lifting for certain amounts of time lead to strength  and muscle size gains. In order to adequately challenge your muscles, you need to put in a lot

of time at the gym. 

If you haven't been sleeping, though, you will not have the same energy level that you would otherwise. This means you won't be able to lift

as heavy for as long.  

If you aren't doing that, then it just isn't doing your muscles any good and you won't be making any progress. 

If you are hoping to gain muscle, then you need to have correct form. Every single weight you pick up will require a certain type of movement. You need to do them

correctly in order to properly stimulate the muscle you are working on. 

Really, move your elbow a few inches to the left and all of a sudden you're working a

completely different muscle than you meant to. 

Having your senses on high alert to always check form is critical. Dulling them by not getting enough sleep is only going to

hurt you in the long run.