Here's how to increase your endurance:

For this example, we'll use a treadmill as our cardiovascular exercise machine of choice. Begin by warming up (walking) for 5 minutes at a slow-moderate pace.

Once the 5-minute warm-up is completed, ensure you are in your target heart rate zone:

220 - age = approximate maximum heart rate (MHR)

You can figure out your "zone" by simply multiplying .65 to .85 times your MHR. For example, a 20-year-old that chooses to go 75% of his or her MHR would have their heart beating 150 times per minute. An ideal range for someone this age is approximately 140 - 160 beats per minute.

Next, gradually increase the intensity of your cardio session by either walking or running faster, or elevating to a hill level. The increments should be by 2 (levels).

Continue on this level for about 2 - 3 minutes. Then repeat the process by increasing the level of intensity over time. The goal is to gradually work your way up to 20 - 30 minutes total.

Be sure to cool down for the last 5 minutes, returning your heart rate to the lower end of your training heart rate zone, and then stretch for 5 minutes.

How much cardio should I do per week?

It's best to start with only 1 - 3 days per week. In time, you may find that you need more or less, depending on your level of fitness or goal.

How do you know if your endurance has been increased?

Ultimately you'll begin to notice that you can sustain a higher level of exertion over a longer period of time. For example, you may notice that you're breathing easier at the 15-minute mark. Whereas before, you were huffing and puffing.