Cardiovascular capacity is an important measure of fitness, it's your ability to move oxygen rich blood to your muscle tissues and allow you to do anything, to move, to ya know, live.

Two Ways to Increase Your Cardio Capacity: 

1. 30 seconds on 30 seconds off, or 60 seconds on 60 seconds off.

 You want the 30 or 60 on to be challenging, so your pace would be faster than your 5km pace. This can be performed on the treadmill or bike. Work your way up to 10 sets. Start with easy 10 minute warm up, and finish with a 10 minute cool down

2. 3:1 x 3.

 So with this one you will work hard for 3 minutes and take one minute rest, repeat 3 times, take a 5 minute rest with easy running or riding, then repeat again. Cool down for 10 minutes
 Add this in to your training program 2x a week for 6 weeks and you will definitely see an improvement in your cardiovascular capacity.