Jumping routines. Resistance bands. Yoga. In an ongoing workout series that begins with this week's look at 49ers safety Tony Parrish, SI will show how NFL players toughen their cores. It's not just six-pack abs they want: A solid core can be the difference between becoming a star and losing your job

By definition, the core is both a foundation and the center of activity. Trainer Mark Verstegen calls it an "erect pillar that funnels energy" through the body. "Core strength is the key for athletes," says Verstegen, who runs Athletes Performance, a fitness center in Tempe, Ariz., that trains scores of NFL players. "Your body uses the core for every movement."

The core muscle group is made up of the abdominals, the lower back, the obliques and the glutes (that is, the buttocks, hips and thighs). A powerful core enables the upper and lower body to work together fluidly, increasing agility and head-to-toe power. The athlete who strengthens his core runs faster, reacts quicker and delivers more punishing body contact. Says the Falcons' DeAngelo Hall, one of the league's most athletic players, "The core runs everything."

Focusing on the core can quickly make even a superior athlete better. Texans defensive end Mario Williams (SI, Aug. 7) weighed 283 pounds and ran the 40-yard dash in the mid-4.7s when he began intense core training last January. Six weeks later he was up to 290 pounds and his time was down to 4.66. He became the No. 1 draft pick. "[Training] is a lot different now," says Buccaneers strength and conditioning coach Mike Morris, noting that core work often includes drills with physioballs and exercises rooted in Pilates, karate and boxing. The 49ers' Tony Parrish, 30, is one of a growing number of NFLers who practice yoga -- the Steelers and the Seahawks offer yoga classes to their players. "[Ten or 15 years ago] we thought about lifting [weights]," Morris says, "not about working the inside first and working your way out."

That's what core strength is about. It takes a strong will to stick to a program, and some need the support of a group. In spring and early summer, dozens of former University of Miami players return to campus and follow an abs circuit devised by Hurricanes strength coach Andreu Swasey that requires them, among other tortures, to do 250 reps of various abs exercises in seven minutes. Arizona Cardinals running back Edgerrin James swears by the circuit, and the value of core work. "There's no reason for me to walk around with my arms and chest swollen from lifting [weights]," says James. "I don't need all that muscle up top. I'd rather transfer it down to the rest of my body. That's where football is played." -- Jeffri Chadiha

"The first class was hard -- I've never been in a room so hot for so long," says Tony Parrish, about his introduction three months ago to Bikram yoga, in which students assume 26 poses in 90 minutes in a room heated to 110° to promote flexibility. Parrish stuck with it, and hot yoga became a staple of his core training regimen. "We tend to bend forward on the field but never do any real backward stretching to counteract that," he says. "To get into and hold each [yoga] position works your abs. My lower back and spine have also gotten stronger and more flexible."

Until the start of training camp, Parrish practiced three times a week at the Bikram Yoga center in Santa Clara, Calif. "I kept coming and got accustomed to it," he says. Parrish, who broke his left ankle and fibula in a game against the Bears last November, says yoga helps him "trust" the injured leg, delivers a "great aerobic workout" -- and builds his core: "I had abs that looked decent but weren't strong. Now there's strength behind them." Here he demonstrates seven poses, breathing evenly through the nose (except when specified otherwise). In trying these exercises, stick to form as closely as possible. Abhinav Sagar, a teacher at the center, describes the benefits of the poses, which are particular to the Bikram philosophy.

Awkward

POSTURE: Feet should be hip distance apart, heels raised, arms straight out, palms down. Squat as if sitting in a chair. Hold for 10 counts, return to starting position. Repeat. ABHINAV SAGAR: "You engage your core for balance. Also strengthens thighs and calves and opens hip flexors."

     Locust

POSTURE: Lie on belly with chin on mat. Put arms underneath body, palms on floor. Raise right leg as high as you can, behind you. Hold for 10 counts. Return to starting position and switch legs. Return to starting position and raise both legs and hips off floor as high as you can and hold for 10 counts. Lower legs and rest on stomach. 20 seconds, face to one side. Repeat all three positions. SAGAR: "This increases flexibility in the spine and stretches your abdominals."

Balanceing Stick

POSTURE: Standing with feet together, raise arms straight up and clasp hands with index fingers pointing up. Step left foot forward two feet, keeping it straight. Point right foot behind you, keeping foot on floor. Bend forward until chest and arms are parallel to floor while also raising right leg behind you until parallel to floor, making a T with body. Hold for 10 counts, return to start position, switch legs. Do two times, each side. SAGAR: "You primarily engage your abdomen in this pose, as well as all your leg muscles. You also develop muscle tone in the shoulders."

Standing Deep Breathing

POSTURE: Stand straight, feet parallel and touching. Interlace fingers and place knuckles under chin with elbows together. Slowly inhale through nose for six counts while raising elbows toward ears. Exhale through mouth, dropping head back, and bring elbows together pointing straight ahead for six counts. Two sets of 10 reps. SAGAR: "It expands the lungs and increases circulation, preparing the body for the movements ahead."

Half Moon

POSTURE: Standing with feet together, raise arms straight up and clasp hands with index fingers pointing up. Push hips left and bend to right, extending left side from hip to armpit. Hold for five counts. Return to center and repeat, bending to left. Return to center, drop head back, arms behind you, hands still clasped and bend backward as far as you can. SAGAR: "The side bend is good for your obliques; the back bend increases flexibility in the spine."

Standing Head to Knee

POSTURE: Lift right leg straight out in front of body, parallel to floor. Interlace fingers and hold under ball of foot. Lean forward, bend elbows and rest forehead on shin. Hold for 10 counts, return to start position and switch legs. Repeat. SAGAR: "You really have to suck in your stomach to get into and hold this forward bend. You engage your core muscles throughout the pose, and it also works your hamstrings."

Standing Bow Pulling

POSTURE: Stand on left leg, bend right leg behind. Grasp instep of right foot with right hand. Extend left arm straight out. Bend forward until abdomen and arm are parallel to the floor. At the same time kick right leg straight up behind you. Hold for 10 counts, return to start position. Switch legs. Repeat. SAGAR: "Firms the abdominal wall, strengthens the lower spine and opens hip flexors. Also promotes general alignment in the body."

Standing Separate Leg Stretching

POSTURE: Start with feet together and step right leg out four feet. Raise arms parallel to floor and turn feet slightly in with knees locked. With straight back bend forward and grab outsides of feet with fingers underneath heels. Touch head to floor. Hold for 10 counts. Return to starting position. Repeat. SAGAR: This stretches all the tendons in the legs.

Cobra

POSTURE: Lying on stomach with feet together place palms flat on floor underneath shoulders with fingers pointing forward. Bring elbows in until they touch sides. Look up towards ceiling and push torso off the floor. Hold for 20 seconds. Lower torso and turn face to one side. Rest for 20 seconds. Repeat. SAGAR: "Increases spinal strength and helps posture. Also works shoulders and upper arms."

Stretching

Posture: Sit with legs extended straight out in front. Raise both arms overhead, reach forward and take hold of big toes with index and middle fingers of each hand. Pull toes towards you while bending elbows toward floor. Hold for 20 counts. Straighten to sitting. Repeat. SAGAR: "This is a flexibility exercise for hamstrings and hip joint".

Bow

POSTURE: Lying on stomach bend knees towards glutes. Reach backwards and grab feet from the outside. Inhale and kick legs up towards ceiling while lifting torso off floor. Hold for 20 counts. Lower torso and turn face to one side. Rest for 20 seconds. Repeat. SAGAR: "Besides strengthening the abdominal muscles, also opens up the rib cage for maximum oxygen intake."

Triangle

POSTURE: Stand straight with arms overhead. Step right leg out to right four feet with arms outstretched, parallel to floor. Turn right foot towards the right and bend right knee until thigh is parallel to floor. Keeping arms straight, bend torso directly to the right. Place fingertips of right hand on the right big toe with elbow flush against knee. Left arm straight up towards the ceiling, palm facing forward. Turn head to look at hand. Hold for 10 counts. Return to lunge position. Step back to start position and switch legs. SAGAR: "This is a great flexibility exercise for the hip joint but also tightens up thighs and works the oblique muscles by holding the side bend. "

-- Lisa Altobelli