The importance of leg training begins with the muscles of the upper leg as the largest and most powerful in the entire body. There are very few sports that don't utilize the strength of the legs as a fundamental. A baseball player, golfer, discus thrower, shot-putter and boxer all need core leg power.
In bodybuilding and weight lifting or powerlifting moves such as the Power Cleans, Clean and Press, and Deadlifts involve a lot of leg drive, as do the lifts in the World's Strongest Man Competition and in Olympic weightlifting competitions.
With this all in mind, there is not one sport in which specifically thigh development is as important as it is to bodybuilding. Above the waist, the judges judge the bodybuilders' shoulders, arms, chest, back and abs.
When the judges focus their attention below the waist, the single most compelling visual element is the thighs, that is well developed quadriceps and hamstrings. The thighs, are easily, the most impressive of all muscle groups in the body and constitute nearly 50% of your body creation.
Could you imagine Sergio Oliva with underdeveloped thighs? Or a Nasser El Sonbaty with chicken legs? Why build impressive 21 inch arms or bigger if they are only built on-top of underdeveloped chicken legs?
Personally, Schwarzenegger notes that when as a youngest, he played soccer and liked to ski. His coached incited him to do Squats, Calf Raises and Lunges to strengthen their core. At this point, Schwarzenegger notes he began to fall in love with bodybuilding at an early age. Upon Schwarzenegger's research into leg development, he hasn't found an athletic coach around the world that doesn't promote the need for great leg strength as an athletic foundation to any sport.
While the legs can be built supremely strong, they are also capable of supreme endurance. The legs- strong enough to move a ton of weight, are also designed to carry one a long distance without tiring.
A person in good shape can run for miles per week training for a 20+ mile marathon and a person in good shape can hike up mountain ranges for miles through rough turf. This duality of the legs is unique to them.
Unfortunately, the leg strength duality requires very much from an aspiring bodybuilder to develop fully and effectively. Not only is large amounts of weight needed to stress the legs, the right amount of sets is also needed to fatigue and recruit the muscle fibers into work. It isn't uncommon for a barbell to be across your shoulders with at least 400 pounds for 8 or 9 reps to get your legs worked out sufficiently. Believe it or not, it doesn't take too long or much effort before you're doing 400+ plus squats. A spotter is essential at these back breaking weights. This well focused leg workout of squats may take a total of ten minutes.
Schwarzenegger notes that in his beginning years of bodybuilding, he neglected his lower body development. Before it was too late, he used the priority principle to target his legs in time for the development of his winning physique. The priority principle is the principle in bodybuilding that states if one area of your physique is lagging behind the rest of your body's development, that lagging bodypart should be trained first on a training day before any other body part. That allows that deficient area to receive a well-rested and non-fatigued human with extra concentration devoted to that lacking body area. That is key in bodybuilding for building up your unresponsive body parts or neglected body parts.
For me, my chest was very unresponsive to heavy stress, so I added more sets and used the priority principle which allowed it to develop better. In addition, reviewing the proper technique and studying bodybuilding frequently lead to greater pumps. Another technique, to really pump the muscles occured when I used a home weight bench. Every hour I'd do a couple sets of 8-10 reps on the hour. When I did that throughout the day, I received incredible pumps, my chest would be huge by the end of the day after frequently sets throughout the hours of the day. I think experiments such as what I did can help you find a secret that works for you.
Unlike most bodybuilders or weightliftings, bodybuilder Tom Platz never had a hard time doing heavy leg development work. He did it with perfect form as well which really paid off. Look at the photo below to see superior leg development.
Perhaps Tom Platz responded too well to heavy squats. It may look like his thighs are perhaps over-developed in proportion to his upper body - a problem rarely seen in the bodybuilding community. I think he is the only example of legs larger than upper body. In this photo, his legs don't look to outta proportion but if you look closely you can really see the mass especially the muscle in his groin area which is quite unique to him.
If you really want to see how outta proportional but impressive legs Tom Platz had, look below. Some even mention that Tom Platz's leg development is better than current era bodybuilder Ronnie Coleman's. There are close in size, with Platz's being a tad bigger and more defined, especially his hamstrings.