The sport of triathlon was born when swimmers, runners and cyclists grew tired of doing just one sport. By combining three events into one, the runners built swimmers' shoulders, the swimmers' gained cyclists' legs and the cyclists became even leaner.

We've created a series of "fitness triathlons" that will help keep your workout fresh while building strength and endurance throughout your body.

THE MULTISPORT TRI

This workout provides all the benefits of a real triathlon, but since you're not competing you'll do the swim last, when it's convenient. No pool? Use a rowing machine instead.

HOW TO DO IT: ride at a steady, comfortable pace - an effort level of five or six on a scale of 1-10 - for 10 minutes. Hop off and run outside or on a treadmill for 10 minutes at the same effort. Finally, head to the pool or rowing machine and do another 10 minutes, again at the same intensity.

MIX IT UP: short on time? Cut the final leg in half and increase your intensity to eight.

THE SPEED-AND-POWER TRI

This builds speed, power and lower body strength.

HOW TO DO IT: choose any three cardio machines that allow you to adjust the resistance or gradient, such as a treadmill, exercise bike or stair-climber. Warm up for two minutes at an effort level of five. Step up your effort to maximum for 30 seconds by increasing the machine's resistance level and/or incline while maintaining the same cadence (the number of revolutions per minute). Return to the warm-up effort level. That's one interval. Do three intervals, then move to the next two machines and do three intervals on each.

MIX IT UP: instead of raising the incline or resistance during your 30-second bursts, pick up the cadence of your maximum effort.

THE USER-FRIENDLY TRI

You can complete this routine in one section of your gym and still challenge your cardiovascular system in new ways.

HOW TO DO IT: choose any three cardio machines, such as a cross-trainer, a treadmill and an exercise bike. On the first machine, do 10 minutes at an effort level of five or six. Move to the next machine and complete 10 minutes at an effort level of nine or 10. Finally, do 10 minutes on your last machine at an effort level of five or six.

MIX IT UP: change the order of the machines each time you train, so the most difficult (middle) segment always provides a new challenge.

THE MORE-MUSCLE TRI

This workout mixes strength training with aerobic work for greater strength and less fat.

HOW TO DO IT: jump rope for 30 seconds, rest for 30 seconds, and repeat five times. Then perform a total body workout consisting of basic body-weight moves, such as squats, push-ups, step-ups, chin-ups and crunches. Do one set of each, without rest. Finish with a 10-minute jog at medium pace.
MIX IT UP: swap the callisthenics for a dumbbell circuit.