Regular cardio is essential to any fitness regime worth it's salt, but it can be really painful if you suffer from bad knees. Your capabilities will depend on the precise nature of the injury, but in most cases,  you can safely perform these cardiovascular exercises without fear that they will aggravate your already vulnerable knees.*

Step-ups

This exercise works your hamstrings, quadriceps, glutes, and your cardiovascular system - and without placing undue strain on your knees. To perform, stand before a staircase, placing one foot flat upon the bottom-most step. Make sure you knee is directly above your heel, then put your entire weight on the heel of the raised foot, step onto it, whilst at the same time lifting the other foot and tapping the step then the floor. Complete 10 repetitions, then switch feet. To make it even more effective, you can do bicep curls with some light weights as you perform the sequence.

Partial squats

Full squats are not recommended for those of you with wonky knees, however partial squats are generally a safe option for building strength and endurance whilst protecting your precious joints. Begin by placing your feet about shoulder-width apart, pointing the toes forward. Flex your abdominal muscles and lower your upper body to the maximum extent possible; the knees should remain positioned behind the toes for the duration of the exercise.

Calf raises

This exercise increases strength and endurance in your lower leg muscles. To perform, stand erect on a flat surface, toes pointing forward; and ankles, hips and shoulders properly aligned. Raise your heels very slowly, then lower. Do 25 repetitions. Note: the slower your raise then lower your body back down, the more effective the workout.

Scissor kick

Work your thighs, hip flexors and abdominal muscles with this exercise. First, lie flat upon your back, keeping your legs together, with arms by your side. Keeping forearms on the ground, raise your legs about six inches, and your shoulders around one inch. Hold that position, then spread apart your legs, before bringing them back to one another, and crossing one leg over the top of the other. Do 50 repetitions.

Swimming

Swimming is one of THE best cardio exercises for people who suffer from knee pain. It really burns through the calories, whilst placing minimal impact on your joints. But the correct form is essential (particularly whilst kicking). Ensure your knees don't remain tense, avoid pushing off the wall as you commence a lap, and avoid techniques like the frog kick) that place undue stress on the knees.

Speed walking

Both people with knee problems and beginner runners should be extra careful when starting to train, which is why they should start with speed walking rather than running. Unlike running and jogging, speed walking is a low impact exercise which still gives a great workout to your entire body. However, at least when starting out, be sure to stick to smooth, flat surfaces. Once your walking muscles are toned and conditioned, you may be able to graduate to low-impact hiking and then to jogging.

Dancing!

That's right, take a dance class! This is a great way to get some cardio whilst placing minimal impact on your knees. It's fun too, and gives you the chance to socialize and meet some new people.

Guest blog post written by: Mathew Foster from KneeSafe.com

*Always consult your physician before beginning a new workout regimen.  Ask your physician if these exercises may be right for you.  Depending on the nature of your knee pain other steps may be neccessary before beginning any workout regimen.