Joseph Diaz Jr.
Weight: 123 lb
Hometown: South El Monte, California
The baby-faced bantamweight Joseph Diaz Jr. (known as Jo-Jo to family and friends) fights at just 123 pounds but has what he calls "man strength" in the ring, boasting a 104–6 amateur record as well as two national championships. What allows Diaz to consistently apply power throughout a fight is his cardio regimen. To get his heart rate up in training, he does five three-minute rounds of sprinting and shadowboxing with one-minute breaks between rounds to mimic fight conditions. "It's intense, but it pays off," Diaz says. For each round, he sprints 100 meters, shadowboxes for about 10 seconds, and repeats until the three minutes are up. Shadowboxing in front of a mirror helps him test his defenses, know what shots to throw, and identify what openings are available after a particular punch is delivered. "If you can beat yourself, you can beat anybody," he says. Has he ever beaten the man in the mirror? "One time I did." (Pictured: Joseph Diaz Jr. at the 2012 Olympic Team Trials in Mobile, Alabama.)
Tae Kwon Do
Weight: 185 lb
Hometown: Sugar Land, Texas
When asked about the most important body part for Tae Kwon Do, Steven Lopez doesn't hesitate. "Legs," says the two-time (2000, 2004) gold medalist, who also won a bronze in 2008. Lopez's are long, muscular, and dangerous: He grew up using them to smash holes in the walls of his parents' garage while sparring with his siblings (two of whom have also competed at the Olympics in Tae Kwon Do). To get the explosive power he needs for his lightning-fast kicks, Lopez does single-leg squats during training sessions that he describes as "barbaric." He'll do three sets of eight squats on each leg, dipping down, then surging back to both feet.
Weight: 190 lb
Hometown: Glendale, Arizona
Drawing a bow and hitting a target from 70 meters with an arrow that travels at nearly 150 miles per hour requires a steady hand, which is why archers learn to anchor themselves to the ground as they prepare to fire. Brady Ellison, the No. 1 archer in the world, builds an unshakable base with leg and core-stability exercises. One of his favorites is a "flexor" drill done while kneeling on BOSU-like balls. Ellison holds a weighted foam bar straight out from his chest and twists his trunk from side to side, pausing at the end of each twist. "It teaches your body to be balanced and have your muscles firing while in athletic position," he says.
Weight: 200 lb
Hometown: Ormond Beach, Florida
In the early days of his career, Phil Dalhausser weighed 180 pounds and was called "the Thin Beast." He has since added 20 pounds of muscle to his beanpole frame, thanks to an intense strength-and-conditioning program. A key exercise for Dalhausser is the burpee. From a standing position, drop into a squat and place your hands on the ground. Kick your feet back to a push-up position, then quickly return your feet to the squat position and jump as high as you can. "I'm in the sand a lot, so popping up quick and getting ready for the next point is pretty important," Dalhausser says. He wears a 25-pound weight vest and does three sets of 15 burpees. (Pictured: Dalhausser in the quarterfinals of the 2008 AVP Crocs Cup in Manhattan Beach, California.)
Track and Field Decathlon
Weight: 210 lb
Hometown: Birmingham, Alabama
Decathletes are the Renaissance men of the Olympics. This summer, the polymath to beat is Trey Hardee, who won the world championship in 2009 and 2011 and was once approached by the New York Jets. Which is what happens when your talents run the gamut. Hardee doesn't have one muscle group he needs to work more than another. "I can't pick one," he says. "Everything is pretty important." Take an event like the shot put: "The more mass you have, the more power you're going to generate," Hardee says of hurling the 16-pound shot. "But it's a delicate balance. The heavier you are, the worse everything in the other events is." Hardee relies on medicine-ball moves that give him explosiveness without bulk. One is a chest pass—stand a few feet from a wall and throw the ball as if you're making a chest pass in basketball. Another is a push-up—put one hand on the medicine ball and do a push-up, then switch hands. Try three sets of eight reps for each exercise. (Pictured: Trey Hardee competing in the long jump of the men's decathlon at the 2011 World Championships in South Korea.)
Weight: 178 lb
Hometown: Tacoma, Washington
A "landmine" is an appropriate exercise for a judo master who trains like he's going to war. Travis Stevens, the best American hope for a men's judo gold, raves about the upper-body benefits of the exercise. Wedge the end of a bar into a corner of a room, slap a plate on the free end, then raise that end of the barbell to head height at a 45-degree angle. Standing in a shoulder-width stance, swing the bar across your chest from one side of your body to the other, lowering it almost to hip height while resisting the movement with your trunk. The exercise is great for back, core, obliques and stabilizing muscles. "Even the shoulders and rotator cuffs," says Stevens, who often bookends his landmines with cleans (explosive movements in which a barbell is lifted from the floor and racked on the shoulders) and pull-ups to create a vicious circuit that helps him withstand combat.
For tips from Michael Phelps and his coach, read our cover story.