Keeping proper running form when you're fresh is usually piece of cake. Maintaining form after a tiring swim and grueling bike ride, well, that's another story. An Australian study of triathletes found that 45 minutes of cycling caused big changes in their knee and ankle movements during the run-changes that sapped enough strength to squash their aerobic capacity. That means more huffing and puffing and a slower finish in your race.

Keep a perfect stride-and shave seconds or even minutes off your time-by making these quick head-to-toe corrections as you transition from bike to run.

Head up: After leaning forward in your aerodynamic pose on the bike, you'll need to fight the inclination to let your head drop down when you start running. That can restrict your airways-but so can tilting your crown too far back. "Keep your head in a neutral position by imagining your sunglasses are aiming a laser 12 feet on the ground in front of you, and you're just pushing that spot forward as you run," says Mike Ricci, owner of D3 Multisport and coach of the 2011 men's triathlon championship team at the University of Colorado.

Shoulders relaxed: For whatever reason, some of us tend to hunch up our shoulders a bit when running, which simply expends unnecessary energy. Every mile marker or so, test your posture by shrugging your shoulders once. "If you can't shrug fully, your shoulders are already too high," says Ricci.

Elbows bent: Carry your elbows at close to a 90-degree angle, with your forearms above waist-level. "When your hands hang lower, your arm effectively becomes a longer pendulum, which is harder for your shoulder muscles to move with each step," says Joe Friel, author of Your Best Triathlonand the founder of the USA Triathlon coaching commission.

Abs tight: If you're slumping forward on your run, it's probably due to a weak core, says Ricci. Strengthen your abs and stabilizing muscles with pushups, leg raises, and overhead squats with a broomstick or unloaded bar for three sets of 10 to 20 reps each, three times a week (even before your endurance training). On race day, your torso should be upright and tight, with a slight forward lean to carry your momentum. "If you try to stay ramrod straight, you're effectively leaning back and putting on the brakes," Ricci says.

Legs quick: The less time your soles are in contact with the ground, the more efficient your stride will be. To do that, you'll want to be running with at least 85 right foot strikes, or 170 total steps, each minute, no matter what your mile pace is. "If you set the bike gear so your cycling rate matches that ideal running cadence, it helps you ease into the right pace after the transition," says Ricci. Think "Lose Yourself" by Eminem or "Take on Me" by Ah-Ha. Then count your pedaling and steps during the bike and run legs of the race while timing yourself for 15 seconds. If you get to 42 or higher in 15 seconds, you're on the right track.

Ankles strong: "Since your steps are quick and short, speed comes from your calves and ankle flex," says Friel. When you want to run faster-either in training to improve your overall pace, or as a kick when you see the finish line-push off more powerfully with your back foot, so that each step propels you farther down the course.

Feet light: You want each foot to land just slightly to the front of your heel pad, so the arch can absorb the impact and help transfer energy into forward motion. "If the heel lands first, you'll just waste energy rolling your whole foot forward," says Friel. To get a better feel for the midfoot strike, Friel suggests running quick drills barefoot on grass or carpet. Start out with three to five 20-second strides, before long runs, one to three times a week, and work up to a set of 6 to 10. Once the correct motion is snugly embedded in your muscle memory, it'll be second nature on race day.