As a personal trainer who started out in the early 2000s, I was initially taught to coach people not to let their knees go forwards of their toes in squats and lunges. Fast forward 15 years and there is a growing movement which believes that is the wrong advice and that we should train our legs in exercises where the knee moves out in front of the foot just as it does in a resting squat position (also known as an asian squat). The split squat is a great exercise to use to do this. We love it because it improves mobility, balance and strength in both legs, plus, as it is a single sided exercise it shows up imbalances in strength, mobility and balance between the left and right legs really quickly, so then we can work to improve the weaker leg to bring about more balance.