The split squat is the basic single leg exercise. In my estimation, it is the single leg movement that should be taught first, before any type of lunging exercise.
Split Squat Problems
A couple problems become evident immediately when a trainee struggles to perform them.
If a trainee is unfamiliar with the movement, they’ll generally struggle a bit in the beginning with good form. There isn’t necessarily any type of physical limitation, they just have to coordinate everything.
When people speed through an exercise, moving quickly can often cover up their lack of balance. Continually staying in motion leaves less chance for falling off balance as compared to when you perform the exercise with a pause at the bottom.
When you make them slow down a bit, be more deliberate, and concentrate on perfect form, lack of balance can readily appear.
Some people are really weak, and they struggle with just their body weight. Others try to use too much weight and their form falls apart. In this case they may not be weak, they just aren’t strong enough to perform the exercise at that weight with acceptable form. I leave very little wiggle room for less-than-optimal form. Getting injured does no one any good.
Tightness in the hip flexors/quads can easily mess up a split squat. People who sit a lot suffer from this problem, as do people with an excessive anterior pelvic tilt, which is often visible as an excessive lumbar curve (lumbar lordosis). You’ll notice an exaggerated arch in the lower back and a butt that sticks out too far. When performing the split squat their torso may collapse forward a bit and complain about discomfort in the front of their thigh or pain at the top of their knee, both in the back leg.
Often, these limitations will work themselves out through foam rolling, dynamic warmups, and the brain gradually accepting a new range of motion.
Some trainees will complain about knee pain in the front leg. This will be the leg that is doing the actual work (some people mistakenly believe that the back leg should be doing the work).
In people who feel pain or discomfort, I often find that foot placement is frequently too close. When the feet are too close together, from front to back, there isn’t enough space for the body to lower straight to the ground. The knee will excessively move forward, and the whole body goes with it. You’ll even see the heel of the front foot rise off the ground sometimes, indicating all the weight has move towards the forefoot.
Even when the shift of the body weight forward is less dramatic, too much weight can be shifted towards the forefoot, leaving the heel without too little weight on it.
Solution: Find Your Heals
When performing the split squat, try to maintain most of your weight from the middle of the foot to the heel. If most of your weight is towards the forefoot, there will be too much emphasis on the quads and uncomfortable forces placed upon the knee which can result in pain.
The simple fix is to maintain a more balanced weight distribution and to push up through the heel. Finding your heel enables the hamstrings and glutes to be more effectively recruited and the forces around the knee joint become more balanced. Knee pain often goes away immediately.
Rule of thumb for the split squat
Put yourself in a position so that your feet are far enough apart to enable your front shin to stay relatively vertical, or just a slight forward tilt, and allows the back knee to stay relatively perpendicular to the ground. Your torso can be vertical (but not leaning back) or with a slight forward lean.
Push up through the heel of the front foot. This will enable better activation of the glutes and hamstrings and keep the knee safer.