Thought I'd share a move for you to try:
The Balance Lunge
Here the model is doing one variation which incorporates the use of a physio-ball. The variation I used on Sunday was putting my back leg on a chair & not using anything for balance.
Regardless here are some key things to pay attention to when using either a chair or physio-ball:
#1 - make sure your front leg is out far enough in front of you to where when you bend, your knee does not go past your toe
#2 - a lunge is more "up & down" movement rather than "forward & back"...focus on not moving your body forward when executing a lunge
#3 - engage your core for stability - even when using the chair you will feel a bit of instability
#4 - you can position your back leg as the model has in the position above or you can up the difficulty by not resting your shin, and soley using the tip of your shoe for balance
#5 - the model is using a chair in front to balance - this is a good starting point, but eventually challenge yourself to not to use anything for balance ~ put your hands on your hips & rep it out!
For beginners - first work on properly executing a lunge without throwing in the balance portion. Once that feels comfortable, move on to perhaps using a Bosu ball...keep your front foot on the Bosu as opposed to your back foot. It will provide just a little instability to make you engage your core & focus on balance.
To advance this even more: incorporate bicep curls or shoulder presses