The most complimentary exercises for runners are cycling and swimming. These two sports are both non-weight-bearing activities, simply meaning that you are not using your entire body to support the full weight of your body, as you do with running. To figure out the amount of time you should engage in a specific cross training activity you need to know the time comparisons between the sports that will ultimately provide the ratios.

CYCLING
Since cycling requires a high level of aerobic conditioning, it is most akin to running. It also allows you to add intensity to your training without putting extra stress on your leg muscles. Although it is best to use cycling as an "active-recovery" day of exercise whereby you cycle at a moderate pace (one that would equal an easy run) you can also do intervals on a bike. This is beneficial to your training because it enables you to get a high intensity workout, without the impact of running.

CYCLING BY THE NUMBERS

• The run to bike ratio is about 1:3, meaning that one mile of running equals three miles of cycling. At 8:00 to 10:00 pace, you'd be running 24 to 30 minutes (respectively) for approximately a three-mile run to equate to nine miles of biking.
• Try to maintain a cadence of 90 revolutions per minute (rpm) that will mimic the optimal stride rate for running of 90 single footsteps per minute.
• Aim for an intensity of 15 to 18 miles per hour.
• Just like in running, if you are cycling outside you will encounter wind and air resistance that will be harder than indoor cycling.
• Stay away from the recumbent stationary bikes, as they put too much pressure on your lower back and make it more difficult to keep the 90-rpm cadence.

SWIMMING
The therapeutic nature of swimming makes it an excellent choice for cross training. Besides the actual fitness that it gives you, swimming (and just being in the water) is a great way to self-treat the inflammation of running. In addition, if you're lucky enough to have a hot tub nearby, you can incorporate contrast baths into your training program. Start with a swim, then proceed to the hot tub for 10 minutes, and finish off with some light stretching in the pool.

SWIMMING BY THE NUMBERS

• The run to swim ratio is about 4:1, meaning that four miles of running equals one mile of swimming. At 8:00 to 10:00 pace, you'd be running 32 to 40 minutes (respectively) for approximately a four-mile run to equate to one mile of swimming.
• Counting your strokes will enable your workout to be more efficient. Aim for 24 strokes in a 25-meter pool.
• Breathe every two to three strokes when swimming freestyle. You'll tire too quickly if you breathe less often. When taking a breath, turn your head just far enough for your mouth to clear the water. Your hips and legs will sink if you turn too far.
• To improve your freestyle stroke, alternate swimming with your fists closed for one lap, then open for the next. This helps your hands develop a feel for the water. Don't begin stroking with one arm until the other one is fully extended in front of you.
• Swimming with fins can increase ankle flexibility and strengthen muscles in the quads, hamstrings, calves and abdomen, all beneficial to runners.
• If you're new to swimming, aim to swim for 15 to 20 minutes. Start by resting for just five to ten seconds at the end of each lap. Your goal should be to eventually swim without taking any rests.