Well defined legs can greatly improve physical appearance and good leg training is vital as legs provide the foundation for the rest of your body.The four main muscle groups in the upper and lower legs are the quadriceps (quads), the hamstrings, the gluteals (glutes or buttocks) and in the lower legs the calf muscles. Looking at each in turn:

Quadriceps

The quadriceps are the group of four muscles forming the front of your thighs.  The best exercise for overall quadriceps definition are squats. Parallel squats are among the best exercises for targeting and defining the largest quad muscle, the vastus lateralis, which runs along the outside of your thighs. Full squats are also among the best for overall quad definition, particularly for targeting the vastus medialis, which makes up the majority of the your inner thigh muscle mass.

Hamstrings

The hamstrings are a group of four muscles that form the back of your thighs and are primarily responsible for bending your knees and extending or straightening your hip joints. Contracted-position hip hyperextension exercises are considered to be the best leg exercises for hamstring definition. Contracted-position hip hyperextension exercises include back extensions, 45-degree hyperextensions, reverse hyperextensions and straight-leg bridges.

Glutes

Your gluteus maximus is primarily responsible for extending your hips and moving your thighs out to the side when your hips are bent. The best leg exercises for lower gluteus maximus definition hyperextend your hips against an aposterior load, which imposes front-to-back resistance. Bent-leg hip hyperextension exercises further maximize gluteus maximus activation by minimizing the contribution from your hamstrings. Straight-leg aposterior hip hyperextension exercises include glute bridges, hip thrusts and single bent-leg reverse hyperextensions. The best leg exercises for upper gluteus maximus definition are seated hip abductions, which require a hip abduction machine that applies resistance as you spread your legs and move your thighs out to the sides.

Calves

The gastrocnemius is the most prominent lower leg calf muscle. Plantar flexion ankle movements activate your gastrocnemius and involve pointing your toes away from your body and flexing your calf muscles. Heavy lever calf raises that quickly exhaust your calves are among the best exercises for building gastrocnemius definition. However, a combination of heavy low-repetition and light high-repetition training might maximize your calf definition. However it should be noted that calf development is strongly genetically predetermined.

Take these exercises and apply them to your workout regimen to build strong leg muscles. You can work your quadriceps into your bicep, tricep and shoulder workout day and work your calves and hamstrings with your back and chest workout day for a perfect workout schedule.