Legs and back make up the majority of overall muscle mass. And have a balanced physique you need to build a huge set of wheels.

Leg day takes a lot of mental energy and preparedness. You need to be rested, fueled, and focused. Also for many legs tend to respond better to higher reps due to legs have more slow-twitch muscle fibers. Of course this varies from person to person. One note on squats; I'm a firm believer of squats for leg mass, however, if you have lower back problems it may be a good idea to substitute them with hack squats (or more sets of leg presses).
Exercise Sets Reps
Squats or Hack Squats 3 12
Leg Press 3 12
Leg Extensions
3 12
Leg Curls (lying, seated, or standing)
3 12
This leg workout consists of basic leg exercises and is great for beginners or if you're taking a breather from your intense workouts. 
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Here's a basic leg workout. Below that you'll find a variety of leg workouts to help you build more mass and enhance muscle definition.
500 Rep Leg Workout - Here's another extremely brutal 'make you puke' leg workout that we did this morning. The focus is on exhausting your quads and hamstrings through high reps and getting the ultimate pump.

Jason's Leg Workout Overload: High Volume Leg Day
- I posted this leg workout the day of the actual workout as I felt it was worthy to posted immediately. This is a brutal high volume, high rep, and high intensity leg workout. You'll crawl away sore from this one. 

Extreme Leg Pump
- This is a leg workout I did after Thanksgiving 2011, after taking a 4 day break from the gym. It incorporates a lot of drop sets for an extreme leg pump.

45 Minute Leg Blast
- Quick yet intense leg workout. Starts with basic heavy leg exercises and ends with an FST-7 style training combined with supersets at the end for your quads and hams.

Massive Leg Workout
- Builds solid muscle mass.

Dynamic Leg Workout - Alternates exercises for quads and hamstrings; encourages equal development between the two muscles groups.

Ultimate Leg Workout - Heavy compound leg exercises combined with supersetting quads and hamstrings towards the end of the workout.

Workouts for Calves - Several workouts for calves.

Leg Workouts

Basic Leg Workout

Advanced Leg Workouts

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