However, it is important to do a lunge properly to avoid putting unnecessary strain on your joints.
Some people avoid lunges altogether because they cause knee pain, but done correctly, lunges can actually help stabilise the muscles that support the knee, alleviating knee pain in the long run.
How to:
Start in a standing position with feet hip width apart.
Take a step forward then lower your back knee to the ground, so both knees are at ninety degrees.
Pause for two seconds then, driving through your front heel, push yourself back to start.