If your legs are not as developed as you want them to be, resistance exercises can help you make desired changes to them. When you build muscle, not only do the muscles actually become bigger, they also get tighter and more defined. You can "thicken" your muscles with the right exercises and the appropriate number of sets and reps. For the legs, you need to work the quadriceps and hamstrings in the thighs, as well as the gastrocnemius and smaller soleus muscles in your calves.
Get Serious with Squats
If you're serious about bulking up your legs, you need to include squats as part of your routine. Squats work almost all of the muscles in your lower body, including the major muscle groups -- the quads, hamstrings and calves. Start in a standing position with your feet slightly wider than hip-width apart and your back straight. Hold a dumbbell in each hand, arms extended straight down at your sides and your palms in. Start squatting as if you were about to sit down in a chair. Keep lowering your body without arching your back or extending your knees past your toes until your thighs are just past parallel to the floor. Hold the position for a moment, stand back up and repeat.
You Won't Lose with Lunges
Lunges are also one of the most effective lower body exercises you can do, and they are essential for helping you build strength in your legs. While holding onto a barbell or dumbbells, stand straight up with a shoulder-width stance. While keeping your back straight, lunge forward with your left leg and lower yourself down. Your legs should both form right angles, your hips should push down toward the floor and your left foot should be flat with your right foot flexed so you're resting on the ball of your right foot. Return to your starting position and then repeat with the other leg for one rep.
Step Up Your Game
To build thick, strong legs, do step-ups, which are an incredibly effective resistance exercise. Stand up straight with a narrow stance in front of a step. For big muscle gains, it's best to use a step high enough so that your leg forms a right angle when you step up onto it. Hold a dumbbell in each hand and extend your arms straight down at your sides. Step up with your left foot, then with your right foot and then step back down, starting with your right foot. Repeat, but lead with your right foot this time.
Glute-Ham Raises for the Win
The glute-ham raise is another essential exercise to include if you want to bulk up your legs. Position yourself on a glute-ham raise machine, so your ankles are between the ankle roller pads, your legs are bent on a right angle and your back is straight. Hold a barbell so it rests against the back of your shoulders. Without arching your back at all, bend over the large padded roller at your waist, lowering down until your hips are fully extended. Raise yourself back up to your starting position for one rep.
Tips for Bulking
Instead of working with a lighter weight and doing more reps, stick with the maximum weight you can manage, and complete fewer sets and reps to bulk up your legs. Three to four sets with five reps in each set is effective. Take a minute or two of rest in between each set. It's also important not to overdo your cardio routines, if your goal is achieving thicker legs. Stick to three to four 30-minute aerobic sessions a week to get the results you want.