Training his core to be a shield strong enough to withstand any strike was the primary purpose behind Bruce Lee's workout regimen. He spent years devising his ab routine, according to Motley Health, and a defined set of abdominal muscles was a an integral part of his persona. Lee employed a variety of ab exercises that he performed daily, substituting one for another in sporadic rotation. He chose up to three maneuvers per workout, fortifying his torso through relentless repetition. Torso Twists Adding a torso twist at the apex of a situp engages the obliques for a more complete core workout. Lee did situp twists in four sets with 20 reps per set. Waist twists are done with an empty weight bar held across the back of the shoulders. These are performed in sets of four, both standing upright and standing with the torso bent at 90 degrees. Each set includes 90 reps, done rapidly with consistent breathing. Maximum ab benefits are achieved if you rotate your torso at least 90 degrees per twist. Frog Kicks Frog kicks are crunch-type movements that can be done on the floor or sitting on a workout bench with legs off to one side. Plant your hands on the floor behind the buttocks or grab the rear edge of the bench. Pull the knees into the chest as close as possible, then extend legs straight out while keeping the torso at a 45-degree angle. Lee performed four sets of 50 at a fast pace, while keeping the abdominal muscles tight the entire time. Dragon Flags Perhaps Lee's most enigmatic abdominal exercise, the dragon flag is recommended for advanced students with an existing degree of core strength. The movements begin as you lie on a bench face-up. Hold the edge of the bench behind the head and raise the legs up toward the ceiling, continuing until your weight is resting on the backs of the shoulders. Lower the feet toward the bench with the legs and back held tense in a slight arc and lift back up again. The feet, legs and lower back do not touch the bench between reps. Lee's workout incorporated four sets of 20 repetitions. Again, don't attempt this move until you've reached an advanced level of fitness. Roman Chair Situps An incline bench is necessary for Roman chair situps, so you can lie back past the parallel plane for added difficulty. Anchor your feet at the front base of the bench under the attached rollers. Cross your arms in the front and lean backward with a smooth movement, then resume an upright position. Inhale when extending back and exhale when sitting up. Lee performed four sets of 20 reps. Considerations Lee also utilized hanging leg raises, floor leg raises, weighted side bends, leaning twists, V-situps and an extensive kicking routine to strengthen and fine tune his abs and core in general. These workout methods can be strenuous and should only be attempted with caution by those prone to lower back problems. Lee also achieved a very low body fat through diet and nutrition, which further accentuated his ab muscles.